b. a. part-i geography title english

SHIVAJI UNIVERSITY, KOLHAPUR

CENTRE FOR DISTANCE EDUCATION

Geography(From Academic Year 2013-14)

Paper-I & II

For

B. A. Part-I

Semester - I & II

H I

K J

Copyright © Registrar,

Shivaji University,

Kolhapur. (Maharashtra)

First Edition 2014

Prescribed for B. A. Part-I

All rights reserved, No part of this work may be reproduced in any form by mimeography or

any other means without permission in writing from the Shivaji University, Kolhapur (MS)

Copies : 300

Published by:

Dr. D. V. Muley

Registrar,

Shivaji University,

Kolhapur-416 004

Printed by :

Shri. B. P. Patil

Superintendent,

Shivaji University Press,

Kolhapur-416 004

ISBN- 978-81-8486-551-6

H Further information about the Centre for Distance Education & Shivaji University may be

obtained from the University Office at Vidyanagar, Kolhapur-416 004, India.

H This material has been produced out of the Developmental Grant from UGC, Distance

Education Bureau, New Delhi.

(ii)

n B. O. S. IN GEOGRAPHY AND METEOROLOGY n

Chairman- Dr. B. N. GophaneVenutai Chavan College, Karad, Dist. Satara

l Dr. P. D. Raut

Head of Department, Geography Dept.

Shivaji University, Kolhapur

l Dr. S. B. Gaikwad

Miraj Mahavidyalaya, Miraj, Dist. Sangli

l Dr. H. Y. Karande

Mahila Mahavidyalaya, Mangalwar Peth,

Karad, Dist. Satara

l Dr. S. S. Kothawale

Padmbhushan Dr. Vasantraodada Patil

Mahavidyalaya, Kavathemahankal,

l Dr. K. A. Mali

Rajaram College, Kolhapur

(iii)

l Dr. A. B. Patil

Arts, Commerce Mahavidyalaya, Ashta,

Tal. Walwa, Dist. Sangli

l Dr. B. L. Ajgekar

Karmvir Hire College of Arts, Science,

Commerce and Education, Gargoti

l Prof. Dr. A. S. Raymane

Benglor University, Bengalore

l Prof. A. S. Jadhav

Geography Department,

Mumbai University, Mumbai.

Centre for Distance Education


n ADVISORY COMMITTEE n

Prof. (Dr.) N. J. Pawar

Vice-Chancellor,


Prof. (Dr.) M. M. Salunkhe

Vice-Chancellor,

Yashwantrao Chavan Maharashtra Open

University, Nashi.

Prof. (Dr.) K. S. Rangappa

Hon. Vice-Chancellor,

University of Mysore

Prof. P. Prakash

Pro. Vice-Chancellor,

Indira Gandhi National Open University,

New Delhi

Prin. (Dr.) A. S. Bhoite

Pro-Vice-Chancellor,


Prof. (Dr.) Cima Yeole

Git Govind, Flat No. 2,

1139 Sykes Extension,

Kolhapur-416001

Dr. A. P. Gavali

Dean, Faculty of Arts and Fine Arts,


Dr. J. S. Patil

Dean, Faculty of Social Sciences,


Dr. C. J. Khilare

Dean, Faculty of Science,


Dr. R. G. Phadatare

Dean, Faculty of Commerce,


Prof. (Dr.) A. B. Rajage

Director, B.C.U.D.,


Prof. (Dr.) D. V. Muley

Registrar,


Shri. M. A. Kakade

Controller of Examinations,


Shri. V. T. Patil,

Finance and Accounts Officer,


Prof. (Dr.) A. R. Bhosale

(Member Secretary)

Director, Centre for Distance Education,

Shivaji University, Kolhapur.

Centre for Distance Education

Shivaji University,

Kolhapur.

B. A. I : Geography

Writing Team

(iv)

n Editors n

Writers NameSem. III

Units

Sem. IV

Units

Dr. H. Y. Karande 1 -

Mahila Mahavidyalaya, Karad

Dr. B. S. Jadhav 2 -

Vijaysinh Yadav Arts & Science College,

Peth - Vadgaon

Dr. A. B. Patil 3 -

Arts, Commerce Mahavidyalaya, Ashta.

Dr. S. D. Shinde 4 -

Dept. of Geography, Shivaji University, Kolhapur

Dr. C. U. Mane - 1

Balasaheb Desai College, Patan

Dr. K. R. Jadhav - 2

Krantisinha Nana Patil Mahavidyalaya, Walwa

Dr. P. V. Patil - 3

Sambhajirao Kadam Mahavidyalaya, Deur

Shri. R. G. Varekar - 4

Smt. Gangabai Khivraj Ghodawat

Mahavidyalaya, Jaysingpur

Dr. B. S. Jadhav

Vijaysinh Yadav Arts & Science

College, Peth - Vadgaon

Dr. S. D. Shinde

Dept. of Geography,


Dr. B. N. Gophane

Venutai Chavan College, Karad, Dist. Satara

Preface

Shivaji University has introduced the Distance Education mode for

external students since 2007-08. I on behalf of Board of Studies in

Geography and Meteorology feel extremely happy to present this book on

'Introduction to Physical Geography' at B. A. Part-I (both semesters). We

hope that we have completed the task quite satisfactorily alloted to us by

the university authoriety.

Syllabus of both the semester is included in this book. We have

introduction of Geomorphology for first semester in which all the fundamental

concepts have been covered. The students may get introduced the basic

knowledge about the earthsurface, where as in the second semester

climatological study is included. Concept of atmosphere, its composition

and components of climates are delt in detail. The last unit is kept for some

practical things; in which only theory of particular practicals is taken into

account.

While preparing this SIM Material for external students as per new

syllabus which is being introduced 2013-14, all the possible care has been

taken.

I on behalf of Board of Studies in Geography and Meteorology grateful

to Prof. N. J. Pawar Hon'ble Vice Chancellor and his officers as well as

Hon'ble Director and his staff of Distance Education of University.

Dr. B. N. Gophane

Chairman, BOS and

Editor SIM

(v)

INDEX

(vii)

B. A Part-I

GEOGRAPHY

Unit No. Topic Page No.

Semester-I : Paper I

Geomorphology

1. Introduction to Geomorphology 1

2. The Earth Crust 12

3. Diostroaphic Movements 34

4. Weathering and Erosion 62

Semester-II : Paper-II

Climatology

1. Atmosphere 79

2. Insolation, Temperature and Atmospheric Pressure 97

3. Winds, Humidity and Precipitation 127

4. Practical (only theory) 152

Each Unit begins with the section objectives -

Objectives are directive and indicative of :

1. what has been presented in the unit and

2. what is expected from you

3. what you are expected to know pertaining to the specific unit,

once you have completed working on the unit.

The self check exercises with possible answers will help you

understand the unit in the right perspective. Go through the possible

answers only after you write your answers. These exercises are not to

be submitted to us for evaluation. They have been provided to you as

study tools to keep you in the right track as you study the unit.

Dear Students

The SIM is simply a supporting material for the study of this paper.

It is also advised to see the new syllabus 2013-14 and study the

reference books & other related material for the detailed study of the

paper.

(viii)

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Unit 1

INTRODUCTION TO GEOMORPHOLOGY

1.0 Objectives

1.1 Introduction

1.2 Presentation of Subject Matter

1.2.1 Introduction to Geomorphology

1.2.2 Definitions of Geomorphology

1.2.3 Nature of Geomorphology

1.2.4 Scope of Geomorphology

1.2.5 Significance of Geomorphology

1.2.6 Recent Trends in Geomorphology

1.3 Summary

1.4 Terminology and Meaning

1.5 Check Your Progress

1.6 Answers to Check Your Progress

1.7 Exercise

1.8 Field Work

1.0 Objectives

1. To understand the Geomorphology.

2. To know the nature, scope and importance of Geomorphology.

3. It helps to state the recent trends in Geomorphology.

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1.1 Introduction

Aim of geography is to study the earth. In this science study the correlation

between natural phenomenon and human being. All the natural phenominon are

called as natural factors. Which includes solid, liquid and gases phenomina. The

solid phenomina called as lithosophere, liquid phenominan called as hydrosphere

and gases phenomenon called as atmosphere. When scope of geography was limited,

all these phenomenon were studied in unique branch but as expanded the scope of

geography all these phenomenon are studied in different branches. The nature of

branches of physical geograph is as given below.

Physical Geography :

♦ Astrology

♦ Geomorphology

♦ Climatology

♦ Meterology

♦ Oceanography

♦ Soil Geography

♦ Geology

♦ Plant Geography

♦ Animal Geography

Geomorphology is an important branch of physical geography which studies

the lithosphere .

The term geomorphology stems from greek words that is geo meaning earth,

morphe meaning form and logos meaning a discourse (description). Therefore,

Geomorphology is science of description of carious forms of the earth surface. The

word Geomorphology firstly used by Kinth in 1894. Before that physical features. This

term was usually used for Geomorphology. But physical features is a broad term whis

includes landforms as well as oceanography, climatology, meteriology also. In brief

geomorphology is a science of earth forms.

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1.2.1 History of Geomorphology

Geomorphology has developed through ancient period. Scholars like

Herodotus, Strabbo contributed for the development of geomorphology and express

that the land forms are results of physical processes. But modern Geomorphology

developed in let eighteenth century. James Hutton, John Play- Fair, and Charles Lyell

state that land froms are creation of exogenetic forces. In twententh century Willum

Moris, Davis, Walter Penck, Lester King developed various theoryes and create

foundation of conceptual view. In let 20th century R.E. Horton, A.N. Straler apply

quantitative method in Geomorphology. The development of Geomorphology was

initiated in Germany and after word that spread all over the world.

1.2.2 Definitions of Geomorphology :

The conceptual thinking and research in Geomorphology was done by various

scholers, several geographers define the discipline Geomorphology. The important

definition are as below :

1. P.G.Worcester (1940) : defined Geomorphology as "the interpretative

description of the relief features of the earth."

2. Von Engeln(1950): Engeln does not consider Geomorphology to be merely

the science of landforms, but also includes in it's fold, the shape of the entire

earth, its configuration and the disposition of its largest units.

3. A.N. Strahlar ( 1958) Geomorphology is an analysis of the origin and evolution

of earth features, Geomorphology does not study merely the physical, chemical

and biological processes affecting the evolution of landforms but also the

structure of the earth crust, the geological processes as well as the climatic

influences, because it is the combined influence of all these factors that

determines landforms.

4. Arthur Bloom- (1979) defines Geomorphology as "the systematic anylasis of

landscapes and processes that change them."

5. B.W. Sparks (1972) : He stated that "essentially it is the study of evolution of

landforms, especially landforms produced by the processes of erosion"

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6. D. Stamp - He stated that "Geomorphology is science of landforms in which

study the shape of earth, evolution and Origin of earth surface.

7. W.G. Moor- He stated that "Geomorphology is a study of physiography of

earth, nature of earth crust and structure of the earth.

1.2.3 Nature of Geomorphology :

Geomorphology is the study of evolution of earth. This study is also done in

several earth sciences, but micro level study of landforms is done in only

Geomorphology. In this study land and oceans are studied broadly descriptive manor,

because these are first order landforms of the earth. The relief features like mountain,

plaetue, plains, ocean floor, continental shelf, continental slepe, oceanic plains, deeps,

trenches etc are second order landform are also studied in this discipline. The relief

features at the third order are the results of exogenetic forces like, vally, canyons,

waterfalls, beaches, sand dunes, cirques etc. are creation of river, wind and glaciears,

these feathers are studied in Geomorphology.

Such study is not possible in laboratory. The whole earth is laboratory for this

study. Therefore, geomorphologist studies the distribution of land and water, explain

their characteristics as well as it’s formation and changes also. The processes of

evolution of land forms, rock structure, composition, and various types are studied in

this discipline.

Geomorphological studies are not only earth movements. Characteristics of

land forms but also anylyse the see shores. Denudation is also another important

aspect of this science. Study of denudation is helpful for analysis of development of

drainage patterns. We can understand the stages of natural cycle of erosion. With the

help of historical account of landforms we can aware about the climate, erosional and

depositional processes in that period.

The above discussion express that the Geomorphology is a major branch of

physical geography and earth sciences. The natural processes are studied in this

discipline. Therefore, the science is concern with soil science, gismography, science

of volcanos, climatology etc. Now a days modern techniques like arial photography,

satilite imeges, remote sencing also used for this study.

Geomorphology is a applied science, because we obsever direct or indirect

impact of landform on human being. Importance of land forms is also marked in

conservation of culture, human activities, human physical characteristics, housing,

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clothing and food habits. The impact of human environment on physical environment

is also important aspect. All there issues studied in Geomorphology conclusively. We

can say Geomorphology is an important discipline for management of natural and

human cultural environment.

1.2.4 Scope of Geomorphology

Geomorphology is a important branch of physical geography, there fore factors

and processes concerning lithosphere studied scientifically in this branch. Factors of

Geomorphology are concern with earth crust. In this discipline includes three major

aspects.

i) dimension and scale of relief features. ii) processes that shape the landforms

and iii) the approaches to the geomorphic studies. The systematic study of landforms

requires some fundamental knowledge of geology. In formation of landforms. There is

major role of geological processes . Geology helps in understanding the nature of

landforms the origin of different types of reliefs like mountains, plateaus continent and

ocean basins, plains.

Thus on the basis of dimension and scale, the relief features of the earth

surface, the core subject matter of geomorphic study. In this contest R.D. Salisbury in

1919 grouped all landforms in three groups. This classification useful for micro level

study of landforms. This classification shows the unity of formation as well as describe

the periodical description.

A. First order landforms : Include the continental platforms and the ocean basins.

The arrangement of continent and oceans appear to be fairly stable, but in

the long geological history of the earth, we come across evidences of many

changes in their form, extension and geographical location.

B. Second order landforms : There are super imposed on the continents and

oceans basins and includes plains, plateaus and mountains on the continental

surface can mid-oceanic ridges, oceanic plains, deeps, trenches , etc on the

ocean floor, besides several features of the continental margins like continental

shelf, continental slope all relief features owe their origin mainly to endogenetic

forces. Especially diastrophism and volcanicity. Although some plains, plateaus

and mountains may be formed by erosional processes. Basically they formed

by endogenetic forces.

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C. Third order landforms : These landforms develop on the relief features of

the second order. Valleys, canyons, waterfalls, beaches, sand dunes, cirques

etc. are examples of relief features of the third order which are the result of

exogenetic forces through process of erosion. These relief features includes

both erosional as well as depositional landforms. A study of these features

occupies a lot of space in Geomorphology.

Except above mentioned features rock formation structure, distribution and

minerals also studies in this discipline. This study is useful for understanding the internal

processes.

First and important stape at studding physical factors of earth is observation.

The information about structure, texture, layers is impossible obtained by observation.

Where inductive method will be applicable. Therefore landform should be introduced

by principle, theory's and hypotheses.

Geomorphology is studied by different views, In ancient period only describe

the landforms, after that distribution of land form was stated. When quantitative

revolution takes place in Geomorphology , accurate measurement was done. This

approach first used in united states in 1940, after that diffused allover world.

Afterward Geomorphology was studied in regional approach. These dynamic

approaches made Geomorphology maximum scientific and conceit results of research.

1.2.5 Significance of Geomorphology

Any discipline is become meaningful, when it is useful for human life. In this

contest Geomorphology is very important science. Which is useful for solve the

problems. There are several crises created in man and environment relation sheep.

These crises could be minimize peacefully with the help of geomorphology.

Geomorphology affects the human activities like agriculture, forest, irrigation, production

of power, mining , Industries, urbanization and urban planning , water supply, transport

and communication, trade etc.

In the contest of environmental resources, Geomorphology is important

discipline. In this sense resource management and impact of them on earth also studied.

The importance of this study is concern to mining of various minerals lines as Oil

mining irrigation and hydal power physvital role.

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H. Verstappen -(1983) has outlined the following areas at interest where

geomorphic knowledge and techniques may be applied for understanding and solving

problems arising out of interaction of man with environment.

1. Topographical and thematic mapping of natural resources.

2. Survey of natural hazards, landslides, avalanches, earthquakes, Vulcanism,

flooding and droughts and natural hazard reduction.

3. Rural development and planning emphasizing land utilization, control of man

induced soil erosion. Channel manipulation and river basin management .

4. Urbanization, mining and construction.

5. Engineering design of transport network, dams, cannals etc.

According to R.J. Chorley (1985) application of Geomorphology can be divided

into two categories.

i) Man as a geomorphicagent.

ii) Geomorphology as an aid to resource evaluation. The unintentional effects of

human economy changes natural landscape for engineering work, mining,

construction of dom and oil drilling etc.

The resource evaluation and planning aspects of applied geomorphology are

concerned with such matter. Geomorphology is useful for invention of resources,

environmental management, evaluation of soil and land, planning for water, prevention

of erosion and mapping of natural disasters and hazards.

1.2.6 Recent trends in Geomorphology

The present status of Geomorphology is the result of gradual but successive

development of geomorphic thoughts postulated in different periods by innumerable

philosophers, experts and geoscientists.

The foundation of modern Geomorphology was postulated by Greek and Roman

philosophers. Herodotus (B.C.485 to BC. 425), Aristotal (BC 384 to BC 322), Strabbo

(54 BC to 25 AD). These scholers contribute valuable contribution in field of

Geomorphology. But the first century to 14th century these 1400 years are known as

dark age. Global unstability and Religious pressure stoped the research activities.

Whole world goes back in educational sector. At the beginning of 18th century education

and research process started againg slowly but silently. James Hutton, Leonardo de

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Vinci , Buffon, Targioni Tozetti and many others geographers and scholars restarted

the research in geomorphy. In this period scientific analysis of landforms was done by

there scholars.

Recent Trends :

Up to beginning of 19th century Geomorphology was a part of physical

geography . After that it begains separate branch of physical geography. From this

period geomorphic thoughts done at local level. In this century the development of

this branch was established in Europe and America.

The european Geographers James Hutton and Sir Charles Lyell postulate

concept of uniformitarism. A. Penck and Bruckner after their observations of Pleistocene

glaciations over the Alps identified four glacial periods during Pleistocene ice age. Sir

Andrew Ramsay presented detailed description of marine platforms made by marine

erosion. After Ramsay B.F. Richtofen made significant contribution in the field of marine

erosion.

In this period American school has credited for making maximum contribution

in the field of Geomorphology. Last two decades of 19th century and first two decades

at 20th century are considered a golden age of American Geomorphology. In this

period W. M. Davis, Major J. W. Powell, Gilbert, Dutton contributed in this discipline.

Powell study of Colorado plateau and uinta mountain suggested geological structure

as a basis for the classification of landforms. He attempted a genetic classification at

landforms. He attempted a genetic classification of river valleys and consequently

classified them. C.F. Dutton was the first geo scientist to use the term isostasy to

denote equilibrium condition of upstanding landmasses of the earth's surface. W.M.

Davin in 1899 postulated theory of cycle of erosion.

The beginning of the 20th century was heralded by methodological revolution

in geomorphological studies. Davis and Perck postulated various theories and explain

every land for is result of processes and time.

Post 1950 geomorphology has undergone more changes in the methods and

approaches to the study of landform. In this period cycle model replace by dynamic

equilibrium model. Qualitative treatment of landforms replaced by quantitative

geomorphology. Inductive method of landforms analysis replaced by deductive method.

Introduction of models and system approach. Emergence of process geomorphology,

climatic geomorphology, applied geomorphology and environmental geomorphology.

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The decade 195- 60 was devoted more for the quantitative study of landforms.

In this period the concept of landscape cycle and hill slope cycle was developed.

At the end of 20th century geomorphology established as applied science.

Every discipline have two major factors. 1) Conceptual and distributional factors 2)

Applied factors. In this contest several scholars develop the conceptual and

distributional factors in this field up to mid 20th century. But let 20th century develop

the applied nature of the geomorphology. Various problems concerning earth studied

in the discipline and sujest remidies for that. This was the begning of applied

Geomorphology.

According to D.K.C. Jones (1980) applied Geomorphology may be defined as

the application of geomorphic understanding to the analysis and solution of problems

concerning land occupancy, resource exploitation, environmental management and

planning. The application of geomorphological techniques and the results of

Geomorphological investigations for resources evaluation, socio-economic

development and mitigation of natural hazards and disasters like flood, earth quake,

volcanos, droughts , land sliding etc. are significant aspect of applied geomorphology

which should be taken into consideration by the geomorphologists. In the field of town

planning, minning, irrigation, and water management this discipling contributers

important role. In 21th century the study of the science not remain traditional, it becomes

modern. Modern techniques are used for anylyase the geomorphic factors. Therefore,

in future this study will be use for solving the various problems of society.

1.3 Summary

Geomorphology is the significant applied branch of physical Geography. It

deals with different land forms of the earth surface, its origin and development. Beside

this the distribution with appropriate description is also studied in this branch of physical

geography. The nature of Geomorphology has been changing time to time from the

era of Eratostheries to today. The recent days quantitative and statistical data as well

as modern technology are applied to reach on particular conclusion. Therefore,

Applicability of geomorphology is increasing and this science become a applied science.

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Land forms : Different relief shape and sized parts of the earth

surface.

Evaluation : Transformation in land forms.

Internal / Indogenic forces : The forces which are originate benith the crust.

External / Exogenetic forces : The forces which are originate on the earth crust.

Oceanic Deposits : Various material deposited on sea floor as per

relief, corresponding with their size.


Que. 1 Choose the correct word and rewrite the sentences.

1) Solid material of the earth crust is known as..................

(a) Stratosphere (b) Soil layer

(c) lithosphere (d) hydrosphere

2) The term Geomorphology stems from .......... language

(a) Lattin (b) Greek

(c) Urdu (d) French.

3) W.M. Davis is famous geographer of ............. nation

(a) U.S.A. (b) England

(c) Germany (d) France

4) Mountains are ................ order landforms.

(a) First (b) Second

(c) Third (d) Fourth

5) Every landform on the earth is result of endogenetic process and ..............

(a) Period (b) River

(c) Exogenitic forces (d) Endogenetic forces.

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1.6 Answers to Check Progress

1) c 2) b 3) a 4) b 5) c

1.7 Exercise

A) Write short notes.

1) Definitions of Geomorphology

2) Importance of Geomorphology

3) Development of Geomorphology

B) Write the answers in detailed of the following questions.

1) Define the Geomorphology and explain its nature and scope

2) Give detail account of development of Geomorphology and modern trends in

the Geomorphology.

1.8 Field Work

1. Observe the different land forms in your surrounding and describe its formation

process with suitable diagram.

v v v

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Unit 2

THE EARTH CRUST

2.0 Objectives

2.1 Introduction


2.2.1 Distributional Characteristics of Continents and Oceans

2.2.2 Alfred Wegener’s Continental Drift Theory

2.2.3 Plate Tectonic Theory

2.3 Summary




2.7 Exercise

2.8 Field Work

2.0 Objectives

1) It helps to know the distributional characteristics of continents and oceans.

2) Wegener’s continental drift theory makes essay to understand the movementsof continents.

3) Through the palate tectonic theory we can know the movements of Plates andits effects on earth surface.

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2.1 Introduction

Different scholars have been propounded different theories about the origin ofthe earth. These scholar’s have their individual perceptions about the earth formationbut one thing is common among them and that is all planets of the solar system arethe byproduct of the sun. As per the scientists’ in historical era in space there was oneprimeval rotating cloud of gas which is today called nebula. The nebula was revolvingaround its axis with high velocity. Due to its velocity and internal collision of particlesgenerated heat and therefore, the temperature and size of nebula is increased. Thenebula started spinning so rapidly that the outer part of nebula thrown in to space.Remaining inner matter of nebula is a sun and outer matter accumulated separatelywhich become the planets. In initial stage the planets release the heat and changed into liquid form there after it become solid. In this way our solar system has been formed.

The earth is one the planet of our solar system with containing biosphere. Theearth surface has distinguishing structures and its one significant character is theorigin of the continents and water bodies. After the earth formation the continents andwater bodies were shaped. According to Chemberlin ‘in the process of cooling of earthsimultaneously some cracks and fissures are developed on the earth surface. Primarystage cracks (silt) and fissure were filled by water and formed the seas. In time beingtemperature of the earth is come down and condition took place and its result is rainfall.The rain water deposited in fissures, volcano crater and low land area of earth surfaceetc. due to those lakes and seas were formed in lot of numbers. These leaks and seaswere expanded and meet each other and slowly converted into oceans.

An elevated portion of the earth surface is come under the influence ofdenudation. The eroded material is lying at sea or ocean floor. Therefore, the weightsof continents are decreasing as well weight of sea floors are increasing. Sea floors arecome under the tremendous pressure of sediments and its results sea floors aredown thrown. But the intense hit is in inner part of earth crust maintain the magamawhich is useful to maintain the equilibrium between land and water bodies.

The distribution of continents and water bodies, its distributional characteristics,continental drift and plate tectonic etc. aspects are the core study matter of this unit.

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2.2.1 Distributional Characteristics of Continents and Oceans

A) Distribution of Continents and Oceans

The continent and ocean are the first order landforms of the earth and it hastheir own importance but these are unevenly distributed. The land and water has coveredsome portion of the earth surface. The portion of the earth surface which is under landis called as continent and the part of earth is under water is called water bodies orocean.

Fig. 2.1 : Distribution of Continents and Oceans

♦ Generally water bodies are covers 2.5 times more area of the earth than theland.

♦ According to Sir John Moore – total area of the earth is about 510 million sq kmand out of this nearly 361 million sq km area is under the water and about 149sq km area under land.

♦ As per estimation of Alfred Wegener – out of the total area of the earth surfacenearly 71.70 per cent is under water and remaining 28.30 per cent area iscovered by land.

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♦ As per the opinion of Kramel 70.80 per cent area occupied by the water bodiesand less area nearly 29.20 per cent covers by the land.

♦ Considering the above all matter it is generally stated that 71 per cent and 29per cent area of the earth surface is under water bodies and land massrespectively.

Fig. 2.2 : Distribution of Land and Water

B) Distributional Characteristics of Continents and Oceans

Through simple observation of World map shows some distributionalcharacteristics of continents and oceans. These are as follows:

1. The distribution of land and water are uneven on the earth surface as well lessarea is under land and vast area is covered by water.

2. Not only uneven distribution of land and water on earth but also unevendistribution in north and southern hemisphere.

3. By simple observation, particularly in the northern hemisphere there is higherproportion of land than the water. Therefore, the northern hemisphere is knownas ‘Land Hemisphere’.

4. As compare to southern hemisphere to northern hemisphere in the respect ofwater proportion. It is observed that the southern hemisphere has occupiedmaximum portion of the earth surface by water. So, southern hemisphere isknown as ‘Water Hemisphere’.

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5. On the earth surface continents are discontinuous e.g. Europe, Africa, Asiaand Antarctica but ocean bodies ate continuous e.g. Pacific ocean, Atlanticocean, Indian ocean and Arctic ocean.

6. In all continents, Asia is the biggest continent and in ocean Pacific Ocean isthe largest ocean among all oceans.

7. On the earth surface the land is nucleus at Caspian Sea and in Pacific oceanat Tahiti island the waters nucleus.

8. The centre of land is water and the water is land.

9. The general shape of continents and oceans are triangular.

10. Concern to continents the base of triangle at north and tapering towards thesouth but its opposite condition in the respect of triangular shape of oceansthe base at south and tapering towards the north.

11. From World map it is indicated that the inclination of continents e. g. North andSouth America towards east, Africa towards west and Asia, Africa and Europeinclined towards north.

12. The area around the North Pole (centre) is covered by water and the areaaround the South Pole (centre) is covered by the land.

13. In northern hemisphere Arctic Ocean has ring of North America, Europe andRussian continents.

14. In south hemisphere Antarctica continent has ring of South Pacific Ocean,South Atlantic Ocean and Indian Ocean.

15. Structural arrangement of continents and oceans are opposite on another e.g.on the opposite of Indian ocean is south America, opposite side of south Atlanticocean is Australia and opposite of Africa and Europe there is Pacific ocean.

16. The continents of the earth are having one island towards the south-east e. g.India has Srilanka, Australia has Tasmania, Africa has Madagascar and Tierradel Fuego is located at southern margin of South America.

17. The continents of the earth have undulating nature of surface. The World’shighest mountain peak Mount Everest (8848 m) in Himalaya and in oceandeepest deep Marianna trench (11033 m) is located in Pacific Ocean.

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C) HYPSOGRAPHIC or HYPSOMETIC CURVE

Sir Jon Moore had been studied the relief features of the earth and its distribution.He was explained that the distribution of continents and water bodies are uneven, theheight of land and depth of seas as well as its structures are different. Firstly he wasused hypsograph to show the distribution of landforms and undulating nature of theearth surface. The graph which is used for demarcating elevation of land and depth ofseas as well its distribution is called hypsography or hypsometric curve.

Fig. 2.3 : Elevation, Depth and Distribution of Surface Land Forms

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Table No. 2.1: Earth’s Landforms – Height, Depth and Distribution

Contents Covered area Water Bodies Covered area

(Height in m) in % (Depth in m) in %

More than 4000 1 0 – 200 5

2000 – 4000 2 200 – 1000 3

1000 – 2000 5 100 – 2000 2

200 – 1000 13 200 – 4000 15

0 – 200 8 4000 – 6000 41

More than 6000 5

Total 29 Total 71

Source: Khatib K. A., Prakrutic Bhugol, 2008.

According to Sir Jon Moore – very less part of earth surface (only 01 %) isunder more elevated land. But less elevated land covered maximum portion (50 %) ofthe continents. Very less area of sea floors is under deepest deeps (only 05 %) as wellvast area of sea floors are covered by plain and its undulating nature and that was 49per cent. With the help of hypsograph it can be easy to represent the sea floor structurelike as continental shelf, continental slope, deep sea plains, ocean deeps and islandswhich is shown in fig. 2.5.

Fig. 2.4 : Relief of Ocean Floor

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Relief of Ocean Floor (Landforms on Sea Floor)

1) Continental Shelf

Continental shelf is that zone of sea floor which lies close to the continentalmargin. Such zone made of the same material as the adjacent land. They vary in widthfrom few meters to the 1300 km. The coast of Ireland it stretches westward for adistance of 80 km and it is more observed at the coast of Siberia it reaches maximumwidth of 1300 km and its depth is varying between 5 m to 200 m. The angles of slopesare different and are usually less where the shelf is widest. The slope is always foundup to 2°.

Continental shelf is shallow part of ocean floor. On it sediments ate continuouslydeposited and sun’s rays are reaching up to its floor. Due to this condition, the vegetationlikes plankton grows naturally. Therefore, such areas are well known for fishing zonesof the World. Beside this continental shelf’s are very rich in power resources e.g.natural oil, natural gas and coal.

2) Continental Slope

Towards sea side after continental shelf second landform on sea floor iscontinental slope. The end point of shelf the slope of ocean floor is increasing andrelatively rapid increase in depth. The angle of the continental slope varies far morethan that of the shelf. The continental slope is varies from coast to coast. Along theIreland coast it is 5° but near the Spain it is much steeper as much as 36°. An averageslope of this feature is 5.5° and the width of continental slope is differing from place toplace.

3) Sea Plains

The third sea floor landform from continental slope which is occupied extensiveplane area is called as sea plane. The sea planes are confined generally on depth of4000 – 6000 m. Such landform is having some hills and also observed at central partsof oceans.

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4) Sea Deeps

The narrow, deep and steep sloppy area of sea floor is known as sea deep. It isalso known as submarine trench. The area of such trenches is generally small. Thedeeps are not usually lie in the middle of the oceans but along the margins of islandsand near the coasts. The Mariana deep in Pacific ocean which is as much as 11033 mdeep close to Guam island. Beside this in the same ocean, trenches are Tonga, Kurile,Aleutian and Sunda trench (7454 m) in Indian Ocean etc. are the some importantocean deeps.

5) Sea Islands

The land mass which is covered by water from all sides is called as island. Onthe basis of size islands are divided into two categories first is small and second is bigislands. The islands which are close to continents these are known as continentalislands e.g. Srilanka and Madagascar. The islands which are situated far away fromcontinents in seas such islands are known as Sea Islands e.g. Mauritius and Hawaii.

2.2.2 Alfred Wegener’s Continental Drift Theory

Alfred Wegener was Garman meteorologist but he had been perfoundedcontinental drift theory in 1912. Due to First World War and its Garman version thistheory almost unnoticed. The second edition of the theory came in English version andit attracted Worldwide attention. The Wegener had supported his theory by providingvarious evidences through scientific manner.

Basically Wegener was meteorologist and he had studied the climatic conditionof the World and he came cross number of evidences which indicate that there havebeen changes in climate in the past. Today Antarctic continent has polar climate whichis under cover of thick ice cover but in past it was in hot climate. Similarly, there aresigns of glaciations in Indian peninsula but today India have tropical climate. Signs ofcarboniferous ice age are also present in South America, Africa and Australia. All theseland masses have hot climate today. These climatic changes he was explained on thebasis of two possibilities:

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1. The sun might be lost its control over the climatic regions due to lead to changein climate.

2. The climatic regions are remained in their original locations but continents aredrifted.

Wegener can’t prove that climatic regions were changed but he had variousevidences to prove second possibility. Thus Wegener’s theory was based on idea ofcontinental drift.

Outline of Continental Drift Theory

According to Wegener – the continents are formed from Sial which has lessdensity. Below this there is Sima and it has more density. Due to such physio-chemicalcondition Sial is floating on Sima. Paleozoic period (40 crore years ago) there wasonly one continent and that was named as Pangaea by Wegener. The Pangaea wassurrounded by vast water body called as Panthalasa. 30 crore years ago or incarboniferous era Pangaea had developed east-west crack and broken into twolandmasses. The northern part of Pangaea named as Laurasia and southern part wascalled as Gondwana. The sea was originated between the Laurasia and Gondwanawas called as Tethys sea. After that Mesozoic period (11 crore years ago) the bothLaurasia and Gondwana landmasses were braking and formed the today’s continents.North America, Europe and Eurasia are the parts of Laurasia and the continents likeSouth America, Africa and Antarctica made from Gondwana landmass. Further in tertiaryperiod (6.5 crore years ago) the Antarctica was braked and present Madagascar, Indiaand Australia have been formed. The Wegener assumed the forces which aregravitational force, force of buoyancy and tidal force breaking the continents and theredrift.

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Fig. 2.5 : Wegener’s Continental Drift

Evidences of Continental Drift Theory

1. Jigsaw Fit

Jigsaw fit is the most significant evidence of this theory. The east coast ofSouth America and west coast of Africa are the best example of jigsaw fit. The bulk ofBrazil is well fit with Gulf of Guinea (African west coast). Today Australia, Africa andIndia are the isolated continents but in their coast have similarities which are built-inone another. Like this east coast of South America can be fitted with west coast ofAfrica. On the ground of jigsaw fit it is conclude that today’s individual continents arethe part of Pangaea. After breaking these continents are drifted and get present positionon the earth.

Fig. 2.6 : Jigsaw Fit

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2. Geological Evidences

There are common geological facts are observed along the east and westsides of Atlantic Ocean. The availability of rocks on continent at particular places haveindentified on other continent which is well fitted to first e. g. north-western part ofAfrica and eastern part of Brazil have a same rock and that’s are basalts. There areanother striking geological correlation on both side of Atlantic Ocean is mountain ranges.The mountain ranges of Appalachian presently found in North America and it alsoappears in Greenland and Europe with same age and type. The same thing is observedon South American east coast and African west coastal area.

3. Paleontological Evidences

In Upper Carboniferous age there were only one continent and as per theclimatic regions of this continent particularly types of animals and plants were origin.Due to the braking of continents and its drift they are placed away from each other withhaving vast water bodies between them. It is commonly observed that the same faunaand flora and their fossils e.g. in Antarctica as well as in all continents of southernhemisphere have contain fossils of lystrosaurus, mesosaurus, glossopteris andsinonouthus. Wegener has been considered that all these areas were contiguous andseparated due to continental drift.

4. Biological Evidences

There are similarities among the animals in the eastern part of North Americaand western part Europe. In the present day after some interval certain living birds ofEurope and Scandinavia have migrating towards the North America. These birds areplunge into Atlantic Ocean. It is a sign of fact that Europe and North America wereconversant with land in past but now they are take apart and have vast water body ofAtlantic ocean.

5. Paleoclimatological Evidences

North-east of USA, England and Antarctica have coal deposits and itself it provesthat there were tropical climate in past but now the percent climate in these lands doesnot indicate such luxuriant growth of vegetation because today these continents havepolar climate. The continents like South America, Africa, India and Australia have been

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showing the signs of glaciations landforms, it reveals that the past climate of theselands were polar but now a day’s these continents have enjoying with hot desert climate.It can be prove the drifting of continents.

6. Proof of Actual Drift

The actual measurements of distance between North America and Greenlandin 1823, 1870 and 1917 have indicated that Greenland is actually drifting towards NorthAmerica at the rate of 32 meters per year. Similarly measurements between Englandand Greenland in 1873 and 1907 have shown that the distance between these areashas increased by 35 years.

7. Young Fold Mountains

As per accordance of Wegener the formation and distribution of young foldmountains have been going on. The North and South America drifts towards the westand its outcome are the formation of Rocky and Andes. Similar to this Himalaya, andAlps mountains were formed due to folding in sediments of Tethys sea. It shows theconvergent of Laurasia and Gondwana.

Critical Evaluation of Wegener’s Theory

1. Most of the scientists have criticized that Wegener did not properly explainedthe forces which was utilized for the breaking the Pangaea and drifting of thecontinents. These scientists are believed that for the breaking of Pangaea thereis need of 1000 times more power than the present power, but such powerdoes not generate from the origin of the earth to present time. If it had suchforce, it would be stopped the earth’s rotation. The rotation of the earth is notstopped till date it reveals such type of powerful force is not origin then how it isas present to product the required effects.

2. According to Prof. Hess, sima layer is formed from the harden material thenthe sial material. If it is considered that sima is made from soft material andthen the sima. Sial is floating on sima then it is happen to continuous processof changing the shape of continents and their locations. But neither changes inthe shape of the continents nor their locations.

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3. The Wegener had been suggested the period of continental drift that periodwas questioned by the number of scholars. The period, in which the braking ofPangaea was taking place, why Pangaea was broken in that particular periodand why Pangaea was not broken before or after that particular period?

4. Wegener had been supporting his theory with jigsaw fit but many scientistshave found faults with it. Only few exceptional locations have this jigsaw fit.The recent studies in such area presents jigsaw fit is available more than 500m depth in the sea water.

Up to some limit Wegener’s theory was criticized but resent studies can beprovide some concrete supports.

1. The magnetic survey of Prof. Laccyti can provide best base for this theory.

2. The recent measurements between the continents are shows the continentaldrifts.

3. The World wide universities and their researches are proving the horizontalmovement in continents.

2.2.3 Plate Tectonic Theory

Introduction

Wegener’s continental drift theory attracted worldwide attention. World’s numberof scholars was involved in the study of continental movements and presented theirviews concern to Wegener’s theory. After 1960, the study of plate tectonic was goingon. Kipping in this mind the plate tectonic theory is recognized as a modified version ofWegener’s theory. Similarly plate tectonic theory is also recognized as a modernmultiform theory or global movement theory.

The concept of plate tectonic was firstly used by Candian Tuzo Wilson in 1965.Who was promoter of the sea floor spreading concept and with this concept he indicatesthe continental drift through faults model, the fault type necessary to make the mobilityof the plates on global work out. According to him structural changes in plates andinter-relations of the outer boundaries of the two or more than two continents or oceanbasins are called plate tectonic and harden part of lithosphere is called plate.

The Royal Society of Londan had organized a symposium which was the officialbeginning of the acceptance of plate tectonics studies. In this symposium, Edward

26

Bullard showed with computer calculation how the structure of continents along botheast and west sides of Atlantic Ocean’s. In 1967, W. J. Morgan had been proposed theplate tectonic theory.

The meaning of tectonic is to construct or structure and plate tectonic meansdue to internal forces results in distinguishing characterized land forms are created onlithosphere. In the process of plate tectonic, there are some common incidences likeas eruption of lava, earthquake, continental movements, folding, faulting, inclinationand deep down of the crust.

Plate Tectonic Theory

The earth crust is discontinuous and simplistically, the earth consists of theplates and plate boundaries, those zones where the plates contact and interact. Thecrust has form from major seven and sub or small twenty plates. Each plate is separatefrom its neighboring plate and independently hovering on asthenosphere. It ischaracterize as a flaccid and the floating continents are made from sial and sea floorscomposed from sima. A plate may be an ocean basin alone or a continent alone or acombination of ocean basin and continent. The plate that outer rigid layer of the earthis divided into couple of dozen ‘plates’.

Major Plates

1) America 2) European 3) Africa

4) Indo-Australian 5) Pacific 6) Atlantic

7) Antarctica

Sub-Plates or Small plates

1) Nazca 2) Cocas 3) Philipiens

4) Caribbean 5) Arabian 6) Bismark

7) Carolina 8) Scotia 9) Juan de fuca

10) Somalian etc.

The current motion of the plates are calculated through remote sensing satellitedata sets and calibrated with ground station measurements.

27

Plate Movements

The earth crust is balancing on the asthenosphere and it is unstable. So, it isfloating in various directions continuously. According to Arther Homes, tremendousforces are in asthenosphere which generates conventional currents in magma whichcauses plate movements. On the earth surface there are presences of sea floormountain ranges, big faults and active folding zones are the best evidences of platetectonics in present era. In the process of plate movements, the plates are contactwith each other by three ways:

a) Convergent Movement

When two plates attracts each other and hit one another is called as convergentmovement. In this process the sides of plates which come in the contact have goesunder the vertical movements. Due to this one plate is thrown upward direction andother plate thrown down ward. Convergent movement plate regions are always pronefor earthquakes and volcanoes e.g. the scientists are in the view of the earthquake of26th December, 2004 at Sumatra, Java, Indonesia and Thailand caused tsunami inBengal Sea.

b) Divergent Movement

Close two or more than two plates are drifting opposite sides are called asdivergent movements. Particularly such movement generally occurs on see floors atthe mountain ranges due this the basaltic magma appears on sea floor and formedthe crust and it can also forming the rift valleys e.g. in middle Atlantic portion there isSurtsey island results of divergent movements. The incidents of earthquake and volcanoare the common and frequently at the plate divergent regions.

c) Parallel Movement

If close two plate boundaries of the crusts are moving back or frontward directionparallel to each other is known as parallel movements. There are damages have beentaking places on parallel boundaries of the plates. The earthquakes and faulting iscommon phenomenon on these region are generally observed.

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Merits and Demerits of the Plate Tectonic Theory

Merits of the Theory

1) The plate tectonic theory can provide the necessary information to betterunderstanding of regional relief features of the earth surface.

2) This theory also gives the useful information about the functions, process andits effects which are responsible for the different changes happening on theearth surface.

3) It is a one kind of source of information to understand the changes on seafloors and its movements.

4) The plate tectonic theory has flash light on the forces those are responsible forthe drifting of the continents.

5) The grate revolution has been taking place in the study of physical geographyafter the formation of plate tectonic theory.

Demerits of the Theory

1) In his theory Morgan didn’t given the actual thickness of the crust. Therefore,how the movements of plates are occurred it becomes a question in mind.

2) The plate tectonic theory does not provide proper information regarding themovements of plats. Is movements of plats occurred in past? If the movementsof plats had taken places in past then its actual period and its nature ofmovements are not explained in this theory.

3) Due to plate tectonic generally mountains are formed but sometimes mountainsare subsided its explanation is not given in this theory.

4) The divergent movement of plate results mountain building on middle portionof sea floor due to vertical movement. But both right and left sides land ofmountain are down thrown then how it is happen?

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2.3 Summary

The origin of the sun to the formation of earth is a matter of curiosity among thescholars. Different scholars have been perfounded their views about the origin of solarsystem. The scholars have the controversy in their views but they are common on onepoint that is the origin of the earth from sun. Today’s state of earth is take place due tothe radiation of hit from earth.

On the earth surface the distribution of continents and water bodies are uneven.Out of the total area of earth surface occupied by the water nearly 71 percent andcontinents are having nearly 29 percent. If we study the distribution of continents andoceans and its distributional characteristics it reveals the various salient features. Thenorthern hemisphere has occupy maximum area under land due to that it is known asland hemisphere and on other side southern hemisphere has occupied more areaunder water than the land therefore it is called as water hemisphere. The appearanceof continents is discontinuous and water bodies are in continuous form. In all oceanbodies Pacific ocean is the biggest ocean and among continents Asia is the largestcontinent. The oceans and continents are in general triangular shape. There are oppositestructural arrangement at North Pole and South Pole, the availability of water on NorthPole and land on South Pole.

The German metrologiest Alfred Wegener was studied the World climate. Hewas observed that the climate of some continents is changed. Kipping this view inmind he putforth the theory of continental drift in 1912. The Pangaea was only onecontinent present in Paleozoic period. The Pangaea was surrounded by vast waterbodies called as Panthalasa. In carboniferous era Pangaea had developed east-westcrack and broken into two landmasses. The northern part of Pangaea named asLaurasia and southern part was called as Gondwana. The sea between the Laurasiaand Gondwana was called as Tethys sea. After that Mesozoic period the both Laurasiaand Gondwana landmasses were braking and formed the today’s continents. NorthAmerica, Europe and Eurasia are the parts of Laurasia and the continents like SouthAmerica, Africa and Antarctica made from Gondwana landmass. In tertiary period theAntarctica was braked and present Madagascar, India and Australia have been formed.The Wegener assumed the forces which are gravitational force, force of buoyancyand tidal force breaking the continents and there drift. The Wegener had given thenumber evidences to prove the continental drift. Beside that some scientists werecriticized on his theory.

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Wegener’s continental drift theory attracted worldwide attention. World’s numberof scholars was involved in the study of continental movements and presented theirviews concern to Wegener’s theory. After 1960, the study of plate tectonic was goingon. Kipping in this mind the plate tectonic theory is recognized as a modified version ofWegener’s theory. Similarly plate tectonic theory is also recognized as a modernmultiform theory or global movement theory.

The plate tectonic theory is recognized as a modified version of Wegener’stheory and it is also recognized as a modern multiform theory or global movementtheory. The concept of plate tectonic was firstly used by Candian Tuzo Wilson in 1965.In 1967, W. J. Morgan had been proposed the plate tectonic theory. The meaning oftectonic is to construct or structure and plate tectonic means due to internal forcesresults in distinguishing characterized land forms are created on lithosphere. Thereare seven major plates and twenty small plates are formed the crust. The movementsof these plates are in three ways and these are convergent, divergent and parallelmovements.


Solar system : Sun and its all planets and sub-planets of planets itscombine system.

Northern Hemisphere : 0° to 90° N. latitude covered part of earth surface.

Southern Hemisphere: 0° to 90° S. latitude covered part of earth surface.

Plates : Part of lithosphere.

Tectonic : Structure, construction or building.

Divergent : Opposite movements

Landforms : Structural arrangement of the earth surface.

Relief : Difference between height and sea level of undulatingsurface of the earth.

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Choose the correct alternative for the following questions:

1. Generally how much area of the earth surface is covered by the water?

(a) 29 Percent (b) 51 Percent (c) 61 Percent (d) 71 Percent

2. On the basis of continent and oceans distributional character which hemisphereis known as water hemisphere?

(a) North (b) South (c) East (d) West

3. Around which land there is concentration of water body?

(a) Red sea (b) Caspian sea (c) Tahiti (d) Arabian sea

4. In general what type of shape has the continents and oceans ?

(a) Spherical (b) Rectangular

(c) Triangular (d) None of these

5. What is the name of island which is located on southern margin of SouthAmerica ?

(a) Tierra del Fuego (b) Malagasi (c) Srilanka (d) Tasmania

6. Which island is situated on south of Africa ?

(a) Tierra del Fuego (b) Malagasi (c) Srilanka (d) Tasmania

7. In which ocean World’s deepest deep Mariana trench is located ?

(a) Pacific (b) Atlantic (c) Indian (d) Arctic

8. Name the ocean which was surrounded super continent Pangaea ?

(a) Pacific (b) Atlantic (c) Tethys (d) Panthalasa

9. Which continent is not formed from the Gonadwana land ?

(a) Europe (b) South America c (c) Africa (d) Antarctica

10. After braking of Gondwana which continent is formed ?

(a) Eurasia (b) Asia

(c) North America (d) South America

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11. By which name the plate tectonic theory is knowned as ?

(a) Continental Drift (b) Global Movement Theory

(c) Cycle of Erosion (d) Gravitational

12. Which is the major plate of the crust ?

(a) Pacific (b) Nazca

(c) Carolina (d) Juan de Fuca

13. What is the name of tectonic movement, if two plates are attracted each other ?

(a) Convergent (b) Divergent

(c) Parallel (d) Convergent and divergent

14. Which is the plate movement results the best example of California’s San Andrisfault ?



15. Which type of plate movement suggested by the scientist, it is occurred atSumatra, Indonesia and Java on 26th December, 2004 ?




1) 71 Percent 2) South

3) Tahiti 4) Triangular

5) Teradelfugo 6) Malagasi

7) Pacific 8) Panthalasa

9) Europe 10) South America

11) Global Movement Theory 12) Pacific

13) Convergent 14) Parallel

15) Convergent

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2.7 Exercise

A) Write in detail answers for the following questions.

1. Write on distribution and distributional characteristics of land and oceans.

2. Describe the structural arrangement of sea floor.

3. Critically evaluate the Wegener’s continental drift theory.

4. Describe the Plate Tectonic theory.

B) Write Short Notes.

1. Distributional characteristics of the land and oceans.

2. The Hypsometric graph.

3. Sea floor structure.

4. The central them of Wegener’s continental drift theory.

5. The merits and demerits of Wegener’s continental drift theory.

6. Jigsaw Fit

7. Plate movements.

2.8 Field Work

1. Study the relief features of your surrounding area.

2. Collect the information through media and internet regarding the earthquake,volcanoes, folding and faults which are recently occurred in World and studyits impact on land of concern region.

3. Collect the temporal imagery of the earth and study the distribution anddistributional characteristics of the continents and oceans.

❖ ❖ ❖

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Unit 3

DIOSTROAPHIC MOVEMENTS

3.0 Objective

3.1 Introduction


3.2.1 Endogenetic and Exogenetic forces and their effects.

3.2.2 Earthquakes : causes, effects, and distribution.

3.3.3 Volcanoes: causes, effects, and distribution.

3.3 Summary


3.5 Check You Progress

3.6 Answers to Check Your progress

3.7 Exercise

3.8 Field Work

3.0 Objectives

1. It helps to understand the information of landforms of the earth.

2. It is useful to know the endogenetic forces and through that we can understandan effects of folding and faulting.

3. It is useful to know the sudden forces and through that we can understand aneffects of earthquakes and volcanoes.

3.1 Introduction

The study of forces affecting the crust of the earth or of geological processesis of paramount significance because these forces and resultant movements areinvolved in the creation, destruction, recreation and maintenance of geomaterials andnumerous types of relief features of varying magnitudes. The surface of the land is

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not uniform in height or in appearance. The different major land forms like mountains,plateaus and plains not only vary in size and shape but they also change with thepassage of time. The surface of the earth is continually changing. The forces affectand change the earth surface. Change is the law of nature. Various structural or relieffeatures come in to existence due to two types of natural processes. These forcesmay be divided into two types.

3.2.1 Internal Forces or Diastrophism :

The forces originate in the interior of earth. They are also known as 'EndogeneticForces', due to intense heat and pressure, different forces develop in the interior ofthe earth. Some of these forces are very slow and their effects are visible only after along period of time. While other forces act suddenly, like earthquakes or volcanismand their effects on the earth's crust are visible within a short period. These forces areresponsible for the formation of mountain and continent (plateaus).

External Forces :

They are also known as 'Exogenetic forces'. These forces develop at the surfaceof the earth and act on the surface only.

Endogenetic or Diastrophic Movements

Endogenetic or Internal Forces

Distrophism includes all the process or forces which disturb and dislocate theearth's crust. The forces coming from within the earth are called as endogenetic forcesand these forces caused by two types of movements in the earth these are horizontal

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movements and vertical movements. Diastropheric forces include both vertical andhorizontal movements which are caused due to forces deep within the earth. Alldiastrophic forces operate very slowly and their effects become discernible afterthousands and millions of years.

Slow Movements

On the basis of their results on the relief features, the diastrophic slowmovements are divided into two groups.

Epeirogenetic or Vertical Movements

This name was derived from Greek word 'Epeiros' meaning a continent. Theseforce act vertically i.e. along the radius either upward or downward from the centre ofthe earth to the surface. They result either in subsidence or uplift of large landmassesin relation to surrounding areas. As a result large continents and plateaus come intoexistence and hence these forces are also known as continent building movements.

Upward Movements

These forces act upwards from centre of the earth. They result in rising of thelandforms. When upward movements act near the coast, the coastal region is uplifted.In this type of uplift, the horizontal layers of rocks are usually not disturbed. There arenumerous examples of emergence of coastal areas in Saurashtra in Gujarat.

Fig. 3.1 : Upward Movement

Downward Force

These forces act downward towards the centre of the earth due to whichsubmergence of landmass take place. These movements are clearly visible near coastalareas. The examples of these forces are at Mumbai and Pondecherry coasts.

Fig. 3.2 : Downward Movement

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Orogenic or Horizontal Movements

The word orogenic has been drived from the Greek word 'Oros' meaningmountain. These movements are responsible for the formation of mountain rangesand hence, the name. These movements work horizontally i.e. at a tangent to thesurface of the earth it resulting in compression and tension in the earth crust. So,these movements are also known as mountain building movements.

Due to horizontal compression takes place in the earth's crust. Horizontalmovements acting towards a comman point produce compression, which forms bendsin the rock strata. If the rocks are comparatively soft while fracture or bends takesplace and if the rocks are hard then faulting is happened.

Thus orogenic movements are of two types these are as following:

a) Folding

b) Faulting

FOLDING

Folding occurs as a result of compressional forces. Horizontal movementsacting towards a comman point produce compression, which forms bends in the rockstrata. These bends are known as folds. Fold mountain come into existence due tosuch folding.

Nature of Fold

A simple fold consists of two distinct parts. The layers of rock that bend upwardsform anticlines while the layers of rocks that bend downwards form synclines. Thesides of a fold are known as limbs. The central line of either fold is known as the axis.Whith the anticlines and synclines, the whole crust appears like a wave.

Fig. 3.3 : Fold

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Types of Folds

The nature of the folds depends on the intensity of the compressional forcesand accordingly the folds attain various shapes.

i) Symmetrical Folds

Fig. 3.4

Symmetrical folds are very simple folds, the limbs (both) of which inclineuniformly. These folds are an example of open fold. When the compressional force iseven from both sides symmetrical folds are formed the slope of both sides are equal.But in real world symmetrical folds are very rarely found.

ii) Asymmetrical Folds

When the compressional forces acting on the same point are of uneven intensity,the limbs of the folds are asymmetrical. The limb is steep along the direction wherethis force is greater while the other limb is gentle slope. Thus, the limbs are asymmetricalin terms of inclinations and length.

Fig. 3.5 : Asymmetrical Fold

iii) Over Fold

When the compressional forces are very intense, the asymmetrical anticline ispushed right over. This is known as an over fold.

Fig. 3.6 : Over Fold

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iv) Recumbent Fold or Overturned Folds

This type of intense folding shows one limb practically resting on another andthe two limbs are more or less in a horizontal position.

Fig. 3.7 : Recumbent or Overturned Fold

v) Overthrust Fold or Nappes

When the pressure exerted on a recumbent fold is great, the rocks may fractureand are bodily carried forward over great distance along the plane of the fracture.Such fold is known as Overthrust fold or Nappe. There are many Nappes in Himalayaand Alps.

Fig. 3.8 : Overthrust Fold and Nappe

vi) Fan Fold or Anticlinorium and Synclinorium

It is large folds in which there are several small folds, anticline has severalanticlines in it and it is known as anticlinorium. Similarly there are several small synclinesin the bigger synclines and is known as synclinorium. Such fold resembles a fan.

Fig. 3.9 : Fan Fold

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Relief Features Produced by Folding

Fold Mountain :

Fold mountains are formed due to folding of rock strata as a result ofcompressional forces. In the past geological ages vast geosynclines came intoexistence. Geosynclines are sea beds or low-lying areas with great thicknesses ofsediments brought down by rivers. When compressional forces acted on geosynclines,the sedimentary rocks strata were compressed and folding resulting into the formationof syncline and anticlines. The anticlines formed the Fold Mountains while synclinesformed valleys. The Himalayas, the Alps, the Rockies and the Andes mountains cameinto existence and these are the best examples of fold mountains.

On the basis of the period of their origin, the Fold Mountains are divided intofollowing groups.

♦ Caledonian Fold Mountain: e.g. Aravallies (India).

♦ Hercynian Fold Mountain: pre carboniferous age e.g. Ural.

♦ Alpine Fold Mountain: e.g. Himalayas, Alps and Rockies etc.

FAULTING

Compressional at one place involves tension at another place and this tensionusually results in the fracture of the earth's crust. Sometimes such fractures alsodevelop due to intense compression. When a fracture takes place, the rocks aredisplaced on either side of it. This displacement is known as a fault. The plane alongwhich the displacement takes place after breaking is known as the fault plane. A faultplane may be vertical, or inclined, or horizontal, or curved or of any type and form. Themovement responsible for the formation of a fault may operate in vertical or horizontalor in any direction. In fact, fault movement or the displacement of rocks occurs onlyupto a few meters only at a time. Fault, in fact, reprents weaker zones of the earthwhere crustal movements become operative for longer duration. There are few termsregarding an ideal fault like fault plane, fault dip, upthrown side, downthrown side,hanging wall and foot wall.

Fault plane is that plane along which the rock bloks are displaced by tensionaland compressional forces acting vertically and horizontally to form a fault. Fault dip isthe angle between the fault plane and horizontal plane. Upthrown side representsthe uppermost block of a fault. Downthrown side represents the lowermost block of

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fault. Hanging wall is the upper wall of fault and foot wall represents the lower wall ofa fault.

Types of Fault :

(i) Normal Fault :

When the inclination of the fault plane and the direction of the down-throw areboth to the left or both to the right the fault is known as Normal fault. Such fault occursdue to the tension.

Fig. 3.10 : Normal Fault

The fault plane is usually between 45º and the vertical. The steep scarp resultingfrom normal faults is called fault-scarp or fault-line scarps the height of which rangesbetween a few meters to hundreds of meters.

(ii) Reverse Faults :

Reverse faults develop due to compression. in this type of faulting displacementtakes place in the upward direction.

Fig. 3.11 : Reverse Fault

Tensional or comprassional forces usually don't produce a single, but producea number of faults that may lie parallel to one another or may make an angle ofvarious degrees with each other. The fault plane , in a reverse fault, is usually inclinedat an angle between 40 degree and horizontal (0 degree). The vertical tress is minimumand horizontal stress is maximum.

(iii) Lateral or strike-slip faults :

These faults are occurred when the rock blocks are displaced horizontallyalong the fault plane due to horizontal movement. These are called left-lateral or sinistralfaults when displacement of the rock blocks occurs to the left on the far side of thefault and right-lateral when the displacement of rock blocks takes place to the right onthe far side of the fault.

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(iv) Step Faults :

Step faults forming on the slope area and all faults are in same direction, thesefaults are called step faults. It is prerequisite condition for the formation of step faultsthat the downward displacement of all the downthrown blocks must occur in the samedirection.

Relief Features Produced by Faulting

1. Horst or Block Mountain

Due to tension or compression, two parallel faults come into existence anddisplacement of rock strata takes place along both the fault planes and a block of theearth's crust is raised between two parallel faults. The upthrown block stands like amountain and it is known as Horst. It is also known as a block mountain. Sometimes,the land on the other sides of the faults slides down along a fault plane leaving thearea in between at a higher level. This portion is also known as a horst. The slope ofhorst is very steep and they usually don't have peaks.

The Vosges Mountain that lie to the west of the Rhine River and the Blackforest plateau to the east of this rive are horsts or block mountains.

Fig. 3.12 : Horst or Block

2. Rift Valley or Graben

A rift valley is also known as graben. When a block of land between two parallelfaults subsides along a fault plane leaving the adjoining areas at a higher level, thesubside part is known as a Graben. In German it means 'Trough'. They are called riftvalley. These valleys have steep wall like slopes and the valley floors are comparativelywider. The Dead sea basin, the Great Rift Valley of East Africa, the Narmada and Tapivalleys are also rift valleys of India.

Fig. 3.13 : Rift Valley or Graben

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SUDDEN MOVEMENTS

Sudden movements originated because of sudden endogenetic forces comingfrom the deep interior of the earth. These sudden movements affect massive destructionon and below the earth surface. These events are like earthquakes and volcanoesabruptly bring about changes in the features of the earth's surface. Such movementsare disastrous hazards when they occur in densely populated regions or places. Butsudden movements like earthquakes and volcanoes create certain relief features onearth surface.

3.2.2 EARTHQUAKE

An earthquake is a sudden, temporary motion or series of motion which originatein a limited region and then spread out from the place of origin in all directions.Earthquakes are tremors which are produced by the passage of vibratory waves throughthe rocks of the earth. If you throw a stone in the well or pond of still water, a series ofconcentric waves are produced on the surface of water. These waves extend out in alldirections from the point where the stone strikes the water. Similarly, any suddendisturbance in the earth's crust may produce vibrations in the crust which travel in alldirections from the point of disturbance.

Definitions :

1) "Vibration or tremors produced in the rocks of the earth crust are known asearthquakes".

2) According to J. C. Macelwane "an earthquake is a vibration or oscillation of thesurface of the earth caused by transient disturbance of the elastic or gravitationalequilibrium of rocks at or beneath the surface".

An earthquake usually originates some kilometers beneath the surface. Thepoint in the crust at which an earthquake occurs is known as the Focus of theearthquake. The point on the earth surface situated above the point of origin is knownas the Epicentre. Vibrations spread in all directions from the focus of an earthquakethey first reach the epicenter.

Fig. 3.14

Seismic Focus

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Earthquake Waves

The earthquake waves are of three types:

i) Primary Waves or Push Waves ('P' Waves)

These waves are like sound caves in which the movement is to and fro in thelines of propagation. The velocity of these waves increases while travelling throughrocks of higher density. They can pass through liquid and solid medium also andvelocity is 10 to 12 km per second.

ii) Secondary or Transverse Waves ('S" Waves)

These waves are similar to light waves where each particle is displaced atright angles to its direction of movement. These waves cannot travel through a liquidmedium and velocity is 8 to 10 km per second.

iii) Longitudinal or Ground Waves ('L' Waves)

These waves travel along the surface of the ground. These waves pass throughthe liquid and solid mass of the earth crust and its speed is about 6 to 8 km persecond.

Fig. 3.15

Causes of the Earthquakes

In ancient times, there was no scientific treatment of the causes of earthquakesand the earthquakes were considered to be the result of supernatural powers andGod's anger against man's sins. But these ideas have no place in the scientific treatmentof the subject in the modern days. Following are considered to be the main causes theearthquakes.

i) Volcanic Activity

When the air compressed within the interior of the earth, escapes out, it shakessome part of the land. In other words, there is a deep relationship of cause and effectto between the two phenomenons. Earthquakes occur at the time of volcanic eruptionsand sometimes earthquakes cause volcanic eruptions. When hot lava, gases, steametc. try to come to the surface due to great pressure in the interior of the earth, itcauses vibrations in the crust and an earthquake is occurred.

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ii) Isostatic Adjustment

The isostatic balance between the raised and depressed blocks of land on thesurface of the earth is not always maintained. When erosion takes place on themountains, it results in deposition on the sea bed and the isostatic balance is disturbed.In order to maintain the balance magma from the neighbouring areas flows under theraised surface and earthquakes occur at zones of weakness. An earthquake takesplace only is the isostatic adjustment is sudden and quick. Such earthquakes normallyoccur in the zone of Young Folded Mountains where the land surface is yet to attainisostatic equilibrium. The example of such earthquake was Uttar Kashi in 1991.

iii) Faults

The tectonic forces including tension and compression cause folding andfaulting in the earth's crust. Tension results in the formation of rift valleys and BlockMountains. When these forces act suddenly, an earthquake is the natural result.

iv) Elastic Rebound

Majority of the earthquakes occur along the fracture line where slipping andsettling down of rock masses takes place. Stresses on the two sides of the faultaccumulate and cause bending of the rocks. When rocks can bear no more stress,breaking with sudden displacement of the rocks on two sides of the fault takes place.It produces a blow to the rocks on one side of the fault-plane and to the lower rocks onthe other side. This is called the elastic rebound hypothesis.

v) Accumulation of Water

Whenever there is large scale accumulation of water, it causes strain in theunderlying rocks. When the strain becomes too much, it breaks the rocks and suddenvibrations take place in the form of an earthquake. Such earthquakes are associatedwith dams, lakes and tanks e.g. earthquake of Koyana (Maharashtra) in 1968.

Vi) Local Causes

Minor earthquakes take place due to local causes such as landslides, emissionof water vapor under high pressure and sudden collapse of roof of the caves in Karstregion etc.

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Vii) Other cause

According to the some geologist, earthquakes originate mainly in the mentle.In this zone, continuous changes are taking place in the crystalline structure of thesilicate minerals due to which localized energy increases. It is of an explosive natureand causes earthquakes.

The earthquakes are measured in terms of their magnitude and intensity. Theearthquake magnitude is related to the energy released during the quake and isrecorded by an instrument called Seismograph. It is measured on the Richter scale.This scale was developed by Charles Francis Richter in 1935. The magnitude isexpressed in absolute numbers, 0-10. The intensity or destructive power of anearthquake is an evolution of the severity of ground motion at a given location. It ismeasured in relation to the effects of the earthquake on human life and is described interms of damage caused to buildings, dams and other structures. The intensity of anearthquake is measured on Mercalli scale developed by an Italian seismologist Mercalliin 1902. The range of intensity scale is I to XII.

Effects of the Earthquakes

Apart from the immediate destruction of life and property, earthquakes bringsseveral changes in and on the earth's crust.

i) Earthquakes cause heveay loss to life and property. The maximum damage iscaused near the epicentre of the earthquake. The most earthquake is the onewhich rocked Bhuj in Gujrat on 26th Jan.2001. Its tremors were felt all over theIndian subcontinent including India, Pakistan and Nepal. It measured 7.9 onthe richter scale. About one lakh people lost their lives.

ii) If the cracks develop in the hilly area, they result in landslides which may blockthe rivers. Sometimes these cracks damage the dams' constructions. The riverwater submerges the surrounding low-laying areas causing severe floods. Theflood in the Brahmaputra valley in 1950 was caused by an earthquake.

iii) Some wells may become dry while other gets more water.

iv) Rivers may change their courses, if fissures develop in their beds.

v) Earthquake occurring in sea, result in high waves in the sea water and causeheavey damages to ships. Such seismic sea waves are called Tsunamis inJapanese. Tsunamis which hit 11 countries surrounding the Indian ocean on26th December,2004 are still fresh in our minds. It was caused a severe

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earthquakes measuring 8.9 on the richter scale and occurring off the coast ofSumatra (Indonesia). Tsunami which struck Japan on March 11 th, 2011 wasalso caused a powerfull earthquake measuring 8.9 on the richter scale on theN.E. coast of Honshu.

vi) Contraction of rock strata takes place, which is evident from the bending ofrailway lines and pipelines.

vii) Earthquakes may form depressions forming lakes.

viii) Fires break out due to earthquakes which inflict great losses.

ix) Glaciers are breached and their avanches scatter too far off places. Thenumbers of ice-bergs increase suddenly.

x) Underground water is also affected by earthquakes.

xi) Due to earthquakes new springs may be appear on the surface.

xii) Earthquake waves are helpful in knowing about the interior of the earth.

xiii) New mineral areas are uncovered or raised up. It provides much needed mineralwealth.

xiv) Rivers adopt new courses which provide new agricultural land.

xv) Faults, thrusts and folds are often associated with earthquakes. An earthquakedisrupted several country roads on the floor of a broad valley in Japan duringthe earthquake of 1891. A tremendous fault occurred during the Californiaearthquake of 1906.

Distribution of the Earthquakes

The distribution of earthquake is more or less similar to that of volcanoes. Noplace on the earth surface is totally free from earthquakes but the earthquakes areoccur more frequently in certain area. These areas are the weak and unstable parts ofthe earth's crust. These belts are as below:

i) The Circum-Pacific Belt

This belt encircle the Pacific ocean and follows the western coast of the Southand North America, Aleution Islands and islands of the eastern coast of Asia likeJapan and Philippines. Nearly 68 per cent of the earthquakes of the world originate inthis belt. This area is known as the 'ring of fire'. This is the area of intense volcanic

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activity also. This area is closely linked with the region of crustal dislocations andvolcanic phenomenon. Mountains here run along the border of continents and nearlyparallel to the depressions in oceans. It causes shar-pest break in relief which becomesa cause for the earthquakes.

ii) Mid-World Mountain Belt

This belt is associated with the young fold mountain ranges of the Alps,Himalayas, and their continuation in the south-east Asian islands. Nearly 22 per centof the earthquakes of the world originate in this belt. It extends parallel to the equatorfrom Mexico across Atlantic Ocean, the Mediterranean Sea, from Alpine-Caucasusranges to the Caspian, Himalayan Mountains and the adjoining lands. This zone hasfolded mountains, large depressions and active volcanoes.

iii) Minor Belts

The remaining 11 per cent of the shocks are recorded outside these two belts.Only a few occur along the fracture in African lakes, Red and the Dead Sea zone.

Fig. 3.16 : World Distribution of Earthquakes

3.2.3 Volcanoes

A volcano is a sudden and abrupt explosion in the crust of the earth throughwhich magma, gas, dust, smoke and solid material is ejected. The hot molten magmabelow the earth's surface is brought to the surface as lava. Lava is at very high

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temperature, varying from 800º to 1300º Celsius and contains steam and severalother gases. All these materials are ejected at great pressure through a pipe which isknown as its 'vent' or 'Neck'. The lava forms a cone like feature on the surface of theearth which is known as 'Volcanic Cone'. The top of the cone has funnel-shaped orsaucer-shaped depression which is known as 'crater'. The diameter of the crater mayvary from a few meters to a few kilometers. Sometimes lava comes to the surfacethrough joints on the sides of the main cone and forms secondary cones. The termvulcanicity includes all the processes through which solid, liquid and gaseous materialfrom the interior of the earth is forced into the earth's crust or is ejected on to surface.The term volcanoes are generally applied to the extrusive type of vulcanicity in whichthe magma reaches the surface of the earth.

Materials Ejected by Volcanoes :

i) Gases :

The gaseous substances are mainly composed of steam, products beinghydrochloric acid, ammonium chloride, sullphur dioxide, hydrogen sulphide, hydrogenand carbon dioxide. Water vapor is the most important of all the gases as it accountsfor 60 to 90 per cent of all the gases thrown out by a volcano. The water vapor causesheavy rainfall after condensation in the atmosphere.

ii) Liquids :

The liquid matters are the lava or magma and water. The temperature of freshlyejected lava may be ranges between 600º C to 1200º C. Water also comes out alongwith lava. The speed of lava flow depends upon its composition, mobility and the slopeof the ground. Usually, the movement is very slow and even a speed of 15 km perhour is rarely achieved. But sometimes the speed may be as high as 80 km per hour.

iii) Solids :

The solid material consists of ash, dust particals and angular fragments mostlyof lava rock blown up from within the vent. If the diameter of the solid block thrown outby a volcano is more than 33 mm it is known as volcanic bomb or blocks. The pipes of4 to 25 mm diameter are known as volcanic lapilli while smaller pieces under 4 mmare called volcanic dust or ash.

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Causes of Volcanoes

Our knowledge regarding the causes of volcanic eruptions is extremely limitedbecause the source of their origin lies deep into the earth. Most of our knowledgeabout the volcanoes is derived from the indirect sources. The major causes aredescribed as under:

i) Percolation of Cold Water

The water percolating through the cracks and fissures in the earth's crust andcomes into contact with the molten or potentially molten rock. Due to high temperaturethe water convert into steam and it required more space. It results into eruption.

ii) Earth Movements

The lava in the interior of the earth is subjected to great pressure which doesnot allow the lava to melt. When the orogenetic forces causing earth movementsaffect the earth's surface, the sedimentary rocks rise in folds. The pressure on lava isreduced and if such zones are weakness. At these places, the lava is melted due toreduced pressure over it and from weak section of earth crust cause the eruption.

iii) High Temperature in the Interior

The temperature found in the interior of the earth is very high. This is due tothe presence of high pressure, chemical reactions and radio-active substances there.It is estimated that the temperature rises in the interior of the earth at the rate of 1°cper 32 meters. Thus the molten material at high pressure comes out at the surface ofthe earth and a volano eruption takes place.

Types of Volcanoes

A) On the basis of the mode of eruption of lava, volcanoes are classified into twotypes.

i) Central Type

When the volcanoes eruption occurs through the single vent or a group ofclosely related vents. It is known as central type of volcanoes e.g. Fuji Yama, Vesuviusare the examples of this type.

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ii) Fissure Type

Volcanic eruption takes place through fissure. Along a line of considerablelength or at numerous points along it. e.g. Deccan Trap.

B) Volcanoes are also classified on the basis of their degree of activity. On thisbasis volcanoes are divided into three types.

i. Active Volcanoes

Those volcanoes that erupt fairly frequently are called active volcanoes.Stromboli and Vesuvius are the examples of this type. The Etna volcano of Italy hasbeen active for the last 2500 years. Stromboli volcano of Sicily Island explodes afterevery 15 minutes and is known as the Light House of the Mediterranean.

ii. Dormant or Sleeping Volcanoes

The dormant volcanoes are that which eruption has not occurred regularly fora long time. But they cause great damage to life and property when they suddenlybecome active after remaining dormant for a sufficiently long time. Visuvius volcanoof Italy has exploded only 10 times in about 1500 years. The volcano of Barren Islandto the east of Andamans in India exploded in 1991 after remaining dormant for severalyears. Such volcanoes are known as sleeping volcanoes. Katmai in Alaska is theexamples of this type.

iii. Extinct or Dead Volcanoes

The volcanoes that have not erupted during historical times and not show anysign of activity are known as extinct volcanoes. The vent of an extinct volcano isblocked and its crater is filled with rain water to form a crater lake. Vegetation startsgrowing on it. The possibilities of future explosion become remote. Popa of Myanmaris its outstanding example and Mount Egmont in New Zealand is the examples of thistype.

Many a time, an extinct volcano suddenly becomes active. This has happenedin case of Krakato volcano. Its eruption in the year 1883 blew off the top of the mountainby an explosion which caused tidal waves about 16 meters high, killing 36000 peoplein west Java. The volcanic dust, ashes and smoke spread in about 27 km, the rockfragments and lava rose to a height of about 800 meters. The volcanic dust and gasesencircling the globe in the atmosphere caused strange sunrise and sunset conditionsfor about three years.

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Effects of Volcano :

Volcanic eruptions cause heavey damage to human lives and property throughadvancing hot lavas and fallout of volcanic materials; destruction to human structuressuch as building, factories, roads, rails, airports, dams and reservoirs through hotlavas and fires caused by hot lavas: floods in the rivers and climatic changes. A few ofthe serve damages wrought by volcanic eruptions may be summarized as given below.

1. Huge volumes of hot and liquid lavas moving at considerably fast speed buryhuman structures, kill people and animals, destroy agricultural farms andpastures, plug rivers and lakes, burn and destroy forest. The great eruption ofMt. Loa on Haawaii poured out such a huge volume of lavas that these covereda distance of 53 km down the slope. The thick covers of green and denseforests on the flanks of Mt. St. Helens were completely destroyed due to severeforest fires kindled by hot lavas.

2. Fallout of immense quantity of volcanic materials including fragmental materials,dusts an ashes, smokes etc. covers large ground surface and thus destroyscrops, vegetation and buildings, disrupts and diverts natural drainage systems,creates health hazards due to poisonous gases emitted during the eruptionand causes killer acid rains.

3. All types of volcanic eruption, if not predicted well in advance, cause tremendouslosses to precious human lives. Sudden eruption of violent and explosive typethrough central pipe does not give any time to human beings to evacuatethemselves and thus to save themselves from the clutches of death loominglarge over them.

4. Earthquake caused before and after the volcanic eruptions generatesdestructive tsunamis seismic waves which create most destructive anddisastrous sea waves causing innumerable deaths of human beings in theaffected coastal areas.

5. Volcanic eruptions also change the radiation balance of the earth and theatmosphere and thus help in causing climatic changes. Greater concentrationof volcanic dusts and ashes in the sky reduces the amount of insolation reachingthe earth's surface as they scatter and reflect some amount of incomingshortwave solar radiation.

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6. A group of scientists believes that volcanic eruptions and fallout of dusts andashes cause mass extinction of a few species of animals. Acid rainsaccompanied by volcanic eruptions cause large-scale destruction of plantsand animals.

Landforms Associated with Volcanoes

i. Volcanic Plateau

Extensive plateaus are formed due to fissure eruption. The piling up of lavaflows on after another result in enormous thickness extending over wide areas. TheDeccan Trap region of peninsular India is a classic example of volcanic plateau.

ii. Volcanic Cones

The volcanic cones are hill-like masses formed around a pipe by theaccumulation of molten rock material and fragments of rock.

Fig. 3.17

On the basis of their shapes volcanic cones are divided among following types.

a) Ash and Cinder Cones

During explosive eruption, fragmental material like dust, ash, cinders and bombsare thrown out from the volcanic vent, again fall back to earth around the vent.

Fig. 3.18

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b) Composite Cones

These are the most common volcanoes that come into existence as a result ofa number of eruptions and hence they take a long time for their build up. These conesare made up of layers of ash and lava e.g. Mount Etna and Vesuvius in Italy andChimborazo in S. America are this type.

Fig. 3.19

c) Shield Volcanoes

At the processes of eruption lava is very mobile and flow over a considerabledistance before it becomes solid. Hence, these volcanoes are not very high and havesmall angles of slope e.g. Hawaii Islands.

Fig. 3.20d) Dome Volcanoes

They come into existence when acid lava is ejected during eruption. The mudlike lava doesn't flow over a long distance and rapidly become cold. Domes of thistype are found in the central Massif of France.

Fig. 3.21

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e) Caldera

A caldera is a remnant of the former crater which was destroyed and a secondcone is built by eruptions of lesser intensity,. Most of the composite cones aresurrounded by the calderas. In Alaska have numerous calderas.

Fig. 3.22

f) Crater Lake

Sometimes the volcanic eruption are violent. The tops of the cones are blownoff forming's a large depression on the top of the volcanic cone. Water may collect inthe crater. It is funnel shaped. Such lade are known as 'Crater lake' e.g. lake Toba inSumatra.

Fig. 3.23g) Volcanic Plug or Greeva

Sometimes solidification of lava takes place in the vent of a volcano. When thesurrounding rock material is removed by different agents of erosion, the vent standsprominently. It is known as a volcanic plug or greeva. The Devil Tower in WyomingState of the USA is the best example of this type.

Fig. 3.24

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1. Distribution of Volcanoes

Most of volcanoes are near the sea coast or on the islands because there aregreat possibilities of percolation of water in these areas. The second important area ofvolcano activity is that of new fold mountains. The mountain building forces have lefta very thin and weak crust in areas of folding and faulting. 486 active volcanoes havebeen found all over the world since 1500 A.D. The total numbers of active and dormantvolcanoes is nearly 800, they mainly occur in the belts or zones. Following are themain volcanic belts of the World.

a) Circum-Pacific Belt

This is the most outstanding volcanic belt of the World in which 403 activevolcanoes are found. This belt more or less surrounds the Pacific Ocean and is knownas 'girdle of fire'. Nearly 66 per cent of the active volcanoes lie in this belt. On the eastcoast of the Pacific Ocean, this belt extends from Cape Horn of South America toAlaska in North America. Along the western coast of the Pacific, this belt extends toKurile islands, Japan and Philippines Islands. It runs through the young fold mountainsof the Rockies and Andies in North and South America and along eastern coastalareas and islands of east Asia e.g. Fuji Yama, Mayon etc.

b) The Alpine-Himalayan or Mid-World Mountain Belt

The belt start from the Canary Islands and stretches through the Mediterraneanand Middle East to south-eastern Asia. Vesuvius, Etna and Stromboli are the famousvolcanoes in this belt.

c) The African Rift Valley Belt

This belt starts from Lake Region to Red Sea in the eastern part of Africa andfurther goes up to Palestine in the north. Belt passes through the Red sea and extendsup to Israel in the north Kilimanjaro in Tanzania in this belt is an extinct volcano. Mt.Kilimanjaro of Tanzania is an extinct volcano and lies out of this rift valley.

d) Other Areas

Some volcanoes are situated in the mid-Atalntic where Cape Verde is veryfamous. Azores,St. Helena, and Ascencion are volcanic islands but they are mostinactive. Islands have about 20 very active volcanoes. Comoro, Mauritius and Reunionare important volcanoes near Madagascar in the Indian Ocean. Some active volcanoessuch as Arelus and Terror are found close to Antarctica. Hawaiian Islands have manyvolcanoes.

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3.3 Summary

The surface of the land is not uniform in height or in appearance. The differentmajor land forms like mountains, plateaus and plains not only vary in size and shapebut they also change with the passage of time. The forces originate in the interior ofearth. They are also known as 'Endogenetic Forces', due to intense heat and pressure,different forces develop in the interior of the earth. Some of these forces are very slowand their effects are visible only after a long period of time.

They are also known as 'Exogenetic forces'. These forces develop at the surfaceof the earth and act on the surface only. Distrophism includes all the process or forceswhich disturb and dislocate the earth's crust. The forces coming from within the earthare called as endogenetic forces and these forces caused by two types of movementsin the earth these are horizontal movements and vertical movements. Diastrophericforces include both vertical and horizontal movements which are caused due to forcesdeep within the earth. All diastrophic forces operate very slowly and their effects becomediscernible after thousands and millions of years.

Folding occurs as a result of compressional forces. Horizontal movementsacting towards a comman point produce compression, which forms bends in the rockstrata. Compressional at one place involves tension at another place and this tensionusually results in the fracture of the earth's crust. Sometimes such fractures alsodevelop due to intense compression. Sudden movements originated because of suddenendogenetic forces coming from the deep interior of the earth.

These sudden movements affect massive destruction on and below the earthsurface. These events are like earthquakes and volcanoes abruptly bring about changesin the features of the earth's surface. Such movements are disastrous hazards whenthey occur in densely populated regions or places. But sudden movements likeearthquakes and volcanoes create certain relief features on earth surface. Earthquakesare tremors which are produced by the passage of vibratory waves through the rocksof the earth. If you throw a stone in the well or pond of still water, a series of concentricwaves are produced on the surface of water. These waves extend out in all directionsfrom the point where the stone strikes the water. A volcano is a sudden and abruptexplosion in the crust of the earth through which magma, gas, dust, smoke and solidmaterial is ejected. The hot molten magma below the earth's surface is brought to thesurface as lava.

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Anticline : A fold in sedimentary strata resembling an arch.

Endogenetic forces : The forces originate in the interior of earth.

Exogenetic forces : These forces develop at the surface of the earth andact on the surface only.

Epeiros : This name was derived from Greek word 'Epeiro'meaning a continent.

Fault plane : Is that plane along which the rock bloks are displacedby tensional and compressional forces acting verticallyand horizontally to form a fault.

Fault dip : Is the angle between the fault plane and horizontalplane.

Upthrown side : Represents the uppermost block of a fault.

Downthrown side : Represents the lowermost block of fault.

Hanging wall : Is the upper wall of fault and foot wall represents thelower wall of a fault.

Earthquakes : "Vibration or tremors produced in the rocks of the earthcrust are known as earthquakes".

Focus of the earthquake : The point in the crust at which an earthquake occursis known as the Focus of the earthquake.

Epicentre : The point on the earth surface situated above the pointof earthquake origin is known as the Epicentre.

Vent or Neck : All these materials are ejected at great pressurethrough a pipe which is known as its 'vent' or 'neck'.

Volcanic Cone : The lava forms a cone like feature on the surface ofthe earth which is known as 'Volcanic Cone'.

Crater : The top of the cone has funnel-shaped or saucer-shaped depression which is known as 'crater'.

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Choose correct alternatives for the following questions.

1. Block mountains are formed by which process?

(a) Epeirogeny (b) Faulting

(c) Volcanic action (d) Denudation

2. Which landform is formed due to subsidence of land between parallel faults ?

(a) Rift Vally (b) Block Mountain

(c) Conical Hill (d) V Shaped Valley

3. Which is the fundamental cause of folding?

(a) Horizontal tension (b) Intrusion of lava

(c) Horizontal compression (d) Vertical Tension

4. What is the meaning of graben?

(a) A down-faulted area (b) A down-folded area

(c) An up-folded area (d) A up-faulted area

5. Which one of the following is an example of endogenic forces?

(a) Erosion (b) Deposition

(c) Volcanism (d) Gradation

6. Which one of the following is not associated with diastropism?

(a) Orogenic process (b) Plate tectoies

(c) Epeirogenic process (d) Gradation

7. Which of the following statements is true about the focus of an earthquake?

(a) It is a point on the surface of the earth.

(b) It is a point inside the earth at a certain depth.

(c) Maximum damage occurs at this point.

(d) It is point of no damage

8. Which of the following statements is true about tectonic earthquakes?

(a) They are caused by sliding of rocks along the fault plane.

(b) They owe their origin to volcanic eruptions.

(c) They occur in mining areas due to collapse of underground mines.

(d) Nuclear explosion causes such earthquakes.

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9. Which type of volcanic eruptions have caused Deccan Trap formations?

(a) Shield (b) Flood (c) Composite (d) Caldera

10. Which of the following is an active volcano?

(a) Stromboli (b) Visuvious (c) Barren Island (d) Popa

11. Which of the following is a part of ring of fire?

(a) Coastalline of Pacific Ocean (b) Alpine-Himalayan belt

(c) The African Rift Valley (d) Mid-Atlantic Ridge

12. Which earthquake waves are very distructive ?

(a) Primary Waves (b) Secondary Waves

(c) Surface Waves (d) Transverse Waves

13. Which of the following instrument is useful to record earthquake frequency?

(a) Thermograph (b) Barograph

(c) Seismograph (d) Pentograph

14. The point of origin of an earthquake is known as ........

(a) Quakecenter (b) Epicenter

(c) Sesmic focus (d) Tectonic point

15. Primary waves of earthquake can travel through the .............

(a) Only solid material (b) Only Liquid material

(c) Only gases material (d) Solid and liquid material.

16. Which is the measuring unit of earthquake intensity ?

(a) Beaufort (b) Richter (c) Mercalli (d) Centimeter

17. At which place, an earthquake of 6.5 magnitude occurred in Maharashtra in1967 ?

(a) Latur (b) Bhuj (c) Koyana (d) Anjar


1) b 2) a 3) c 4) a 5) c

6) c 7) b 8) a 9) b 10) a

11) a 12) c 13) c 14) c 15) d

16) b 17) c

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3.7 Exercise

A) Broad Questions :

1. Give an account of the endogenetic forces ?

2. What is an earthquake? Explain the causes and effects of the earthquakes ?

3. Describe the different types of folding with suitable diagrams ?

4. Write the causes and effects of volcano ?

5. Explain the distribution of earthquake ?

B) Short Notes :

1. Types of fold 2. Types of fault

3. Effects of fault 4. Effects of earthquakes

5. Distribution of earthquakes 6. Distribution of volcanoes

7. Causes of Volcanoes

3.7 Field Work

1. Visit an earthquake affected area and collect information of effect of anearthquake.

2. Observe surrounding hill landforms or visit Mahableshwar and observe volcanicdepositional features and describe it.

3. Collect additional information of earthquakes, volcano and tsunami throughpaper cutting, magazines and internet.

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62

Unit 4

WEATHERING AND EROSION

4.0 Objectives

4.1 Introduction


4.2.1 Weathering : Meaning and Types

4.2.2 Concept of Cycle of Erosion

4.2.3 Erosional and Depositional Features of River and Wind

4.3 Summary



4.6 Answer to Check Your Progress

4.7 Exercise

4.8 Field Work

4.0 Objectives

1. To understand the meaning and types of weathering.

2. To study the concept of cycle of erosion.

3. To know the erosional and depositional features of river and wind.

4.1 Introduction

In the last chapter we discussed the endogenetic forces make the surface

uneven and exogenetic forces destroy the raised portions and level them down. The

exogenetic forces through weathering and erosion destroy the relief of the earth’s

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surface. In this unit we will discuss the meaning and types of weathering, concept of

cycle of erosion and erosional and depositional features of river and wind.


4.2.1 Weathering : Meaning and Types

Rocks, generally formed inside the crust are subjected to different types of

physical and chemical changes when they exposed and come into contact with the

atmospheric moisture and temperature conditions prevalent there. This process is

called weathering. Weathering is a static geomorphological process which is important

for the soil formation.

We can explain meaning and concept of weathering with the help of definitions.

According to Sparks : “Weathering is the mechanical fracturing and chemical

decomposition of rocks, insitu by natural agent at the surface of the earth.”

Weathering is the process of dissinteration and decomposition of rocks insitu.

Types of Weathering :

There are three main types of weathering which are as follows :

1) Physical / Mechanical Weathering

Physical weathering break rocks into smaller pieces without changing their

chemical composition. Physical weathering attack exposed rock and can penetrate

into rock along cracks, joint and bedding planes. The action of water and changes in

temperature are most important agents of physical weathering.

(a) Temperature Changes and Expansion

This process effective where temperature is high in day and very low at night.

The minerals in rocks expanse in the day time due to high temperature and contract at

the night due to low temperature. The differential expansion and contraction create

tension between minerals leading to the breaking of rock.

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(b) Freezing, Jhawing and Frost Wedging

This process is most effective at high elevation in mid latitude where freezing

and melting is often repeated. Frost weathering occurs due to growth of ice within

pores and cracks of rocks during freezing and melting. When water enters in rock and

freeze it expands by about 9%, creating pressure on rock. Repeated cycle of freeze-

that cause fragmentation of rock in the form of block, scree and talus.

(c) Exfoliation

Exfoliation is a type of weathering where scaling of rocks takes place. This

process results in curved sections of exposed rock peeling off from the core. This is

known as spheroidal weathering when caused by chemical factors.

2) Chemical Weathering

Chemical weathering decomposes the rock mass to form new minerals and

substances. Solution, Hydration, Oxidation and Carbonation are leading chemical

processes affecting on rocks.

(a) Solution

The water or acid with dissolved content is called solution. This process involves

removal of solid in solution which depend upon solubility of mineral in water. Soluble

rock forming mineral like potassium, sulphate, nitrate etc. are affected by this process.

Minerals like calcium carbonate and calcium magnesium bicrabonate present in

limestone are soluble in water. Common salt is also a rock forming mineral is susceptible

to process of solution.

(b) Hydration

In this process water is added into minerals, due to addition of water into

minerals it expands, it causes an increase in the volume of rock.

e.g. Calcium sulphate takes in water it turns to gypsum.

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(c) Carbonation

In this process minerals that contains calcium, sodium are changed to

carbonates by the action of carbonic acid is known as carbonation, calcium carbonate

and magnesium carbonates are dissolved in carbonic acid and carried away in solution.

(d) Oxidation

Oxidation means a combination of a mineral with oxygen to form oxides. When

the rock affected contain iron, the ferrous state in which iron commonly occurs changes

or oxidizes to ferric state and the crust crumbles. It takes place very rapidly in the

presence of water.

3) Biological Weathring

The weathering which is caused by action of organism is called as bilogical

weathering. This can physically break down rock or lead to chemical attack.

(a) Faunal Weathering

The burrowing animals like worms, gophers, rabbit, rats, jackle etc. help in

gradual breakdown or fragmentation of rock. Small organisms play more important

role in rock and soil weathring.

(b) Floral Weathering

Weathering of rock by vegetations takes place in two ways i.e. (i) physical

weathering and (ii) chemical weathering which is called as biochemical weathering.

Root of plants make cracks in rock which lead to disintigration of rock. The

decomposition of organic matter produces humic acid, and respiration by soil organisms

produces CO2 which combines with water and form carbonic acid. These acids can

become concentrate in soil and accelerate chemical weathering.

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Fig. 4.1 : Weathering Types

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Importance of Weathering

The soil is formed by weathering, without which vegetation could not grow and

all animal life depends upon vegetation. Weathering helps to the erosional process.

Continuous removal and transfer of weathered material lead to gradual lowering of the

surface.

4.2.2 Concept of Cycle of Erosion

W. M. Davis an American geomorphologist emphasized that the landform evolve

and degrade in a cyclic manner. Davis postulated his concept of cycle of erosion in

1899 to present genetic classification and systematic description of landforms.

Geographical cycle is a period of time during which an uplifted landmass

undergoes its transformation by the process of landsculpture ending into low featureless

plain or peneplain. Davis explained these stages in the context of the landforms made

through the action of river, therefore cycle of erosion also called the fluvialo cycle of

erosion.

Fluvial Cycle of Erosion

In the ideal condition the cycle of erosion denotes sequential changes in

landform from youth to old stage.

Youth Stage

This stage is characterized by a few consequent trunk streams, a few large

tributaries and rapid rate of vertical erosion because of steep slope. V shaped valleys,

rapids, waterfall are formed in this stage.

Stream divides will be broad and stream meandering exist in this stage.

Mature Stage

In this stage vertical erosion or valley deepering is remarkably reduced. This

stage is heralded by lateral erosion and well integrated drainage network. The lateral

erosion leads to valley widening which transform ‘V’ shaped valley into wide valley.

Flood plain, natural levees, meanders are formed in this stage.

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Old Stage

In this stage a landmass has been reduced by erosion almost to base level,

such a erosional plain is called ‘Peneplain’, sometimes the peneplain may be interrupted

by an isolated hill, such a erosional remnants of this type are called monadnocks.

Criticism :

1. Davis’s view was purely descriptive.

2. His cycle was not based on precise measurements or observations.

3. The approach was qualitative.

4.2.3 Erosional and Depositional Features of River

Running water is a major gradational agent that are constantly work in shaping

the land. As an agent of gradation running water perform both the function of erosion

and deposition. The rainwater reaching the earth’s surface becomes runoff. The runoff

becomes a stream when water flow from certain height. The geological work of fluvial

processes taken place into 3 ways erosion, transportation and deposition. The fluvial

landforms are divided into two major groups i.e. (1) erosional landforms and (2)

depositional landforms.

Erosional Landform

The significant landform resulting from fluvial erosion by streams are river valley,

waterfall, pot holes, rapids etc.

(a) River Valley (‘V’ Shaped Valley)

The valley formed in Youth Stage of river. The valley is deep and narrow, both

valley sides meet together at valley floor. The valley formed due to accelerated rate of

vertical erosion.

Valleys are divided into two types i.e. Gorges and Canyon.

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A Gorge is a deep valley with very steep to straight sides and canyon is

characterized by steep step-like side slopes. It is extended form of canyon e.g. different

‘V’ shaped vallies formed by Himalayan Rivers.

(b) Waterfall

Waterfall defined as a vertical drop of water of enormous volume from a great

height in the long profile of river. Waterfall formed due to sudden descent break in the

longitudinal course of river, like variation in the relative resistance of rock (soft - hard

rock chain).

e.g. Gersoppa fall, India, Angel fallin Venezuela etc.

(c) Pot Holes

The Kettle like depression in the rocky bed of river valley is known as pot holes.

Pot holes are generally cylindrical in shape. The pot hole drilling is the mechanism

through which the grinding tools (boulder, pebbles etc.) when caught in the water

whirling, the diameter of pot holes ranges between from few centimeters to several

meters. Pot holes of bigger size is called as plunge pool. Various plot holes are formed

over Chhota Nagpur plateau.

(d) River Meanders

“The bends of longitudinal course of the river is known as meanders.” In the

mature stage of river meander loops develop with deposition inside each loop. Overtime,

the size of meanders is increased leading to the widening flood plain.

(e) Structural Benches

The step like flat surface formed at either side of lowest valley floor. The benches

are formed due to differential erosion of alternate band of soft and hard rock.

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Depositional Landforms

River deposit eroded material when the velocity of water decrease. Deposition

caused due to sudden decrease in slope.

The heavy material is deposited first and smaller and coarest sediment

suspended load deposited after.

(a) Bars

Bars are ridge like features, which forms inside the bank of ends.

(b) Alluvial Plan

Itis expanse of flat land on either side of river. When a river floods its banks and

spills on to its flood plain, it leaves behind a layer of alluviam / sediment. This sediment

enriches the soil, forming an alluvial plain.

(c) Ox-bow Lake

The lake is formed due to impounding of water in the abondoned meander loop

is called as Ox-bow lake. It is formed during flood time, when portion of channel cut off,

as the stream tends to seek a straighter path.

(d) Natural Levees

“The belt of ridges built by the deposition of sediment by river on its either bank

is called natural levee”. Levees are formed due to deposition of sediment during flood

period. Average height of natural levees is within 10 meters.

(e) Delta

The traingulart shape alluvial tract at the mouth of river is called delta. Delta

formed when the sediment supply is high and there should be absence of tidal, current

and waves action. There are various types of delta like Arcute delta, Bird foot delta,

Estuarine delta, Cuspate delta etc.

e.g. Bird foot delta of Mississippi.

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Fig. 4.2 : Depositional Features of River

4.2.4 Erosional and Depositional Features of Wind

Wind is less effective gradational agent than river, sea waves, ground water

and glacier. Wind is an effective in desert areas. Wind erosion is limited to few meters

from ground surface. Wind is a significant gradational agent and contributes to the

shaping of the landforms. The landform created by wind are called Aeolian Landforms.

Erosional Landform of Wind (Aeolian Landforms)

Wind is an major erosional agent in desert or arid area. Wind erosion is taken

place by abrasion, deflation and attrition processes. These processes or action

produces ventifact, mushroom-rock, zeugens, yardang etc.

(a) Ventifacts

Faceted rock cobbles and pebbles abraded by long periods of wind erosion are

called Ventifacts.

The rock pieces having three abraded facets are called Dreikanter.

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(b) Yarding

Yarding are steep sided deeply undercut overhanging rock ridges separated

from one another by long corridors. Yarding are formed when alternate bands of hard

and soft rocks are vertical. They are parallel to each other.

(c) Zeugen

These are rock masses of tabular form look like a capped ink pot standing on

softer rock. These are formed where alternate bands of hard and soft rock are in

horizontal manner.

Fig. 4.3 : Features Produced By Wind Erosion (Abrasion)

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(d) Mushroom Rock

The rock of broad upper part and narrow base look like a umbrella or mushroom

is called mushroom rock. The base of rock eroded vigorously from all side because of

direction of wind not a constant. The upper part of rock least affected by erosion. The

mushroom rocks called ‘Gara’ in Sahara.

(e) Deflation Basin

Depression is formed in desert due to removal of sand due to process of deflation

is called deflation basin / blow outs. The size of these basins varies from few meters

to kilometer.

Depositional Landforms of Wind

Wind transport the load by suspension, saltation and traction processes. When

obstructions occurs in the direction / way of wind then wind deposite the material on

either side of obstacles. Due to deposition of sand various landforms are formed like a

Ripple mark, Dunes, Sand drift etc.

(a) Ripple Mark

These are small scaled depositional feature of sand. They are wave like feature

and formed due to saltation process.

(b) Sand Dunes

Heaps or Masses of sands are called sand dunes. These are formed because

of accumulation of sand due to obstruction in wind speed. The dunes are mobile they

are not stable.

(c) Seif

This is one of the type of dunes. These are longitudinal sand dunes. Windward

side of these dunes is gentle while leeward slope is steep.

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(d) Barchan

These are crescent shaped dunes having two horns. The winward side of this

dunes is convex and leeward side is concave. In areas of abundant supply of sand,

barchans are large and well developed.

(e) Loess

Loess is wind blown silt. It is fine grained sediment with small clay fraction and

higher content of carbonate mineral. Loess deposits very distant place from the source

areas. Loess deposits are seen in China, Alaska, Europe etc.

Prevailing wind

Fig. 4.4 : Features Produced by Wind Deposition

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4.3 Summary

Weathering is a static geomorphological process involves dissintegration and

decomposition of rocks in situ. For the convenience of study weathering is physical /

mechanical chemical and biological weathering. The type and rate of rock weathering

is influenced by a rocks mineral makeup.

The work of a river includes erosion, transportation and deposition creates

number of erosional and depositional features.

The work of wind is dominant in the arid and semi-arid regions of the world and

it also creates different erosional and depositional features on the surface of the earth.


1) Base Level : The surface of a lake or a river or a sea into which

it flows.

2) Deflation : The process by which wind remove particles of dust from

the land surface in an arid region.

3) Erosion : The incorporation and transportation of material by a

mobile agent usually water wind or ice.

4) Peneplain : An area of low relief developed at the end of ageomorphic

cycle under humid fluvial conditions.

5) Hydraulic Action : The denudation by the force of moving water against

solid rock.


A) Choose the correct alternatives for the following questions.

1. Decomposition and Disentigration of rock insity is known as ........

(a) Erosion (b) Weathering (c) Mass Movement (d) None of these

2. Solution is the effective in a .............. terrain.

(a) basaltic (b) granite (c) shaly (d) limestone

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3. Clacium sulphate changed into gypsum by ..............

(a) Hydration (b) Carbonation (c) Oxidation (d) Solution

4. The concept of cycle of rosion propounded by ...........

(a) Davis (b) Penck (c) Strahler (d) Hutton

5. Waterfall formed in ................ stage.

(a) Old (b) Mature (c) Youth (d) None of these

6. Natural Embankment found along river banks, build up during flood period is

called .............

(a) Levee (b) Peneplain (c) Ox-bow lake (d) None of these

7. ................. is erosional features produced by rivers.

(a) Alluvial plain (b) Ox-bow lake (c) Potholes (d) Delta

8. Meanders are ..............

(a) products of weathering of Rock

(b) waves produced along a sea shore

(c) bend along the longitudinal course of river

(d) deposition feature of wind.

9. Loess is commonly formed by the deposition of ................

(a) Wind (b) Wave (c) River (d) Volcano

10. Barchan are found in .................. areas.

(a) Limestone (b) Arid (c) Coastal (d) Glaciated

11. Longitudinal sand dunes are called ..............

(a) barchan (b) seif (c) spit (d) yarding

12. The process of which blow outs formed in arid region is called .........

(a) degradation (b) abrasion (c) attrition (d) deflation

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1. (b) 2. (d)

3. (a) 4. (a)

5. (c) 6. (a)

7. (c) 8. (c)

9. (a) 10. (b)

11. (b) 12. (d)

4.7 Exercises

A) Broad Questions

(i) What is Weathering ? Discuss the different types of weathering.

(ii) Describe the erosional features produced by wind.

(iii) Critically examine the cycle of rosion as given by W. M. Davis.

(iv) Explain with examples depositional features produced by river.

B) Short Notes.

(i) Biological Weathering

(ii) Delta

(iii) Depositional Landforms of Wind

4.8 Field Work

1. Collect information about the types of weathering in your surrounding area.

2. Observe the erosional and depositional features of river.

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b. a. part-i geography title english

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