lecture#10a geomorphology

8/2/2019 Lecture#10a Geomorphology

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Lecture #10GEOMORPHOLOGY

Jasmi Ab TalibGeoscience & Petroleum Engineering Department

Physical GeologyQAB1013


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TODAYS LEC TUR E &OUT

COM

E1. W ill concentrate on two main processesthat modify the earth surfaces

Endogenic Processes Exogenic Processes

2 . Towards the end of lecture, you will be able

to differentiate and recognise, in great detailbetween endogenic and exogenic .


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GEOMORPHOLOGYGeomorphology (f rom Greek : , ge , "earth"; ,morf , "f orm"; and , logos , "knowledge") is thescienti f ic study o f land f orms and the processes thatshape them. Geomorphologists seek to understand whylandscapes look the way they do: to understandland f orm history and dynamics, and predict f uturechanges through a combination o f f ield observation,physical experiment, and numerical modeling .Geomorphology is practiced within geology , geodesy ,geography , archaeology , and civil and environmentalengineering . Early studies in geomorphology are thef oundation f or pedology , one o f two main branches o f soil science .


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T he science which studies the nature and history o f land f orms and processes; weathering, erosion anddeposition which created them.

Geomorphology what is it?study o f Earth sur f ace processes and land f ormsa historical science, interested in the origin and

evolution o f land f orms

study o f currently active processes & past processes

W hat shapes the Earths sur f ace?

GEOMORPHOLOGY


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S haping the Earth

A mong the processes that drive the shaping o f land f orms is platetectonics , or the shi f ting o f large, movable segments o f lithosphere(the crust and upper layer o f Earth's mantle ). Plate tectonics isdiscussed in detail within its own essay and more brie f ly in other areas throughout this book, as be f its its status as one o f the key

areas o f study in the earth sciences.O ther processes also shape land f orms. Included among theseprocesses are weathering , the breakdown o f rocks and minerals ator near the sur f ace o f Earth due to physical or chemical processes ;erosion , the movement o f soil and rock due to f orces produced bywater, wind, glaciers, gravity, and other in f luences ; and masswasting or mass movement , the trans f er o f earth material, byprocesses that include f low, slide, f all, and creep , down slopes . A lsoof interest are f luvial and eolian processes (those that result f romwater f low and wind, respectively) as well as others related toglaciers and coastal f ormations.


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GEOMORPHOLOGICAL PROCE SS ES


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GEOMORPHOLOGY AGENT SGEOMORPHOLOGY AGENT S

A ny natural medium capable o f securing andtransporting earth materialT hey remove materials f rom one part o f the

earth s crust and transport and deposited themelsewhere- R unning water - Groundwater - Waves, currents, tides, and tsunami- Wind- Glaciers


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GEOMORPHOLOGY AGENT S

Groundwater

W ind

Glaciers

W aves

Tsunami

Running water


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Geomorphic ProcessesGeomorphic ProcessesGeomorphic processes are all those physical and chemical changes whiche ff ect a modi f ication o f the earth s sur f icial f orm

T he processes are dynamic processes at work in the earth's land f orms andsur f aces. T he mechanisms involved, weathering, erosion, and platetectonics, combine processes that are in some respects destructive and inothers constructive.

Processes may conveniently be divided into those that originate within theEarth (endogenic processesendogenic processes ) and those that originate externally(exogenic processesexogenic processes ).

A) Endogenic Processes

B) Exogenic Processes


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Geomorphic ProcessesGeomorphic ProcessesA) Endogenic Processes

T he ri f ting o f the great lithospheric plates,the continual dri f ting o f continental crust,and the expansion o f oceanic crust f rommidoceanic spreading centres all set deep-seated dynamic f orces into action.Diastrophism is a general term f or allcrustal movements produced by endogenicEarth f orces that produce ocean basins,continents, plateau, and mountains.


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Geomorphic ProcessesGeomorphic ProcessesA) Endogenic ProcessesT he so-called geotectonic geotectonic cyclerelates these larger structuralf eatures to gross crustalmovements and to the kinds o f rocks that f orm various stages o f their development.

Exa mples of endogenic processes mount a ins a nd oce a nic b a sins building.

A folded mount a inbelts evidence for crust a l deform a tionby Ea rths intern a l forces.


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Geomorphic ProcessesGeomorphic ProcessesA) Endogenic Processes

O rogenesis,O rogenesis, or mountain building,tends to be a localized process thatdistorts pre-existing strata.Epeirogeny Epeirogeny a ff ects large parts o f thecontinents and oceans, primarilythrough upwards or downwardmovements, and produces plateau andbasins.

F olded mount a in belts


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GEOLOGY OF S E A S IA ( after Tjia, 2005)


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0 100 200 km

S e s a r A l u r L e b e y

S e s a r B

o k B a k

S e s a r K u a l a L u m p u r

S e s a r B

u k i t T i n g g i

S e s a r L e b i r

S e s a r M e r s i n g

S u t ur aB

e n t o n g- R a u b

BATUANMETA S EDIMEN

KARBON

BATUAN S EDIMEN

PERM

BATUAN

META S EDIMENPERM

M aj or F a ults in Peninsul a M a l a ysi a


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Geological ProcessesGeological ProcessesA) Endogenic Processes

Geysers and hot springs, like volcanoes, are o f ten f ound in tectonically unstable areas . Volcanoes are produced by outpouring o f lavas f rom deep within the Earth.

Examples: the Columbia plateau o f the western U nited S tates is overlaid by volcanicbasalts that are more than 3,000 m thick and cover 52,000 sq km. S uch plateau basalts arederived f rom f issure volcanoes.


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O ther kinds o f volcanoes include shield volcanoes , which are broad and convexin pro f ile, such as those f orming theHawaiian Islands, and strato volcanoes ,such as M ount Fuji or M ount S t Helens,which are composed o f interleavedlayers o f diff erent materials.


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FREQUENCY OF OCCURRENCE OFEARTHQUAKE S

Descriptor Magnitude Average Annually

Great > 8 1 M ajor 7 - 7.9 17

S trong 6 - 6.9 134 M oderate 5 - 5.9 1319

Light 4 - 4.9 13,000(estimated)

M inor 3 - 3.9 130,000(estimated)

Very M inor 2 - 2.9 1,300,000(estimated)

Based on observations since 1900. Based on observations since 1990.

(J a ba t a nM

eterologi M

a l a ysi a , 2005)


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EARTHQUAKEEARTHQUAKE ACTIVITIES AROUND M ALAYSIAACTIVITIES AROUND M ALAYSIA


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I mpacts of earthquakesTsunami


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T he earthquake, measured atabout 8.0 by the U nited S tatesGeological S urvey in Hawaii,struck at 7:40 A .M . local time(10:40 P. M . S unday G MT ).

T he survey placed theepicenter 6.2 miles under theocean and 25 miles f rom thecoastline.

S ING A P OR E, A pril 2 A power f ul undersea earthquakein the S outh Paci f ic early todaysent huge tides rolling acrosslow-lying areas o f the S olomonIslands, inundating entirevillages and causing anunknown number o f deaths,local o ff icials reported.


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R ecent earthquake around our region


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WeatheringMechanical weathering is thebreakdown o f rock into particleswithout producing changes in thechemical composition o f theminerals in the rock.

Ice is the most important agent o f mechanical weathering. W ater percolates into cracks and

f issures within the rock, f reezes,and expands. T he f orce exertedby the expansion is su ff icient towiden cracks and break o ff pieces o f rock.

I nside Lo w er Antelope C a nyon, looking out w ith the sky ne a r the top of the fr a me. Ch a r a cteristic l a yering in the s a ndstone isvisible.

Heating and cooling o f the rock, and the resulting expansion and contraction, alsoaids the process.

M echanical weathering contributes f urther to the breakdown o f rock by increasingthe sur f ace area exposed to chemical agents.

Exogenic Processes


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Geological ProcessesGeological ProcessesB. Exogenic Processes


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Geological ProcessesGeological Processes

W e a thering, bre a kdo w n of rocks by physic a l a nd chemic a l processes a t the surf a ce, or in the top fe w metres,of the Ea rths crust. I t is the initi a l st a ge in the denud a tion (lo w ering of the l a nd surf a ce) of l a ndsc a pe, w hich

produces debris kno w n a s regolith. This c a n subsequently be tr a nsported awa y by such a gents of erosion a srunning wa ter, ice, the w ind, or the se a .T w o m a in types of w e a thering c a n be identified. Physic a l or mech a nic a l w e a thering bre a ks rocks into sm a ller fr a gments w ithout ch a nging their chemic a l composition. Chemic a l w e a thering decomposes the rock m a ss toform ne w miner a ls a nd subst a nces. Ho w ever, both chemic a l a nd physic a l w e a thering c a n a lso be brought

a bout by the a ctivity of pl a nts a nd a nima ls, in w hich c a se it is referred to a s biologic a l w e a thering.

An inselberg resulting fromw e a thering of the outer p a rt of the rock ma ss.

B. Exogenic Processes


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WeatheringChemical weathering is the breakdown

of rock by chemical reaction. In thisprocess the minerals within the rock arechanged into particles that can be easilycarried away.A ir and water are both involved in manycomplex chemical reactions.

T he minerals in igneous rocks may beunstable under normal atmosphericconditions, those f ormed at higher temperatures being more readilyattacked than those which f ormed atlower temperatures. Igneous rocks are

commonly attacked by water, particularlyacid or alkaline solutions, and all o f thecommon igneous rock f orming minerals(with the exception o f quartz which isvery resistant) are changed in this wayinto clay minerals and chemicals in

solution.

I gneous rocks w e a thered into s a ndy cl a yey soils a nd gr a vels, w hich a re the m a in sourceof modern sediments


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S pheroidal weatheringS pheroidal weathering is a type o f chemical weathering that creates

rounded boulders and helps to createdomed monoliths

S pheroidal weathering occurs whenever a mass o f rock (most typicallygranitic in composition), experiences a drastic reduction in ambient heat andpressure, such as when a batholith is exposed at the sur f ace. R ock f orms atgreat temperatures and pressures (760 C and 300 M Pa, f or granitic rock),and in granites there are three mutually perpendicular sets o f joints thatdevelop when this overburden is removed. Two things cause this in granites:the quartz crystals expand about 5%, and acidic water attacks the f eldspar minerals, turning them into clay . T hus the corners become rounded, becauseangular edges provide more than one area o f attack by exposing a greater amount o f sur f ace area. Edges and especially corners o f an angular block

weather f aster than f latter sur f aces.


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5 . Oxidation

Process o f combining with oxygen; will increase in +ve valence or decrease in ve valence.eg. A lteration o f iron f rom the f errous.

4Fe O + O 2 2Fe 2O 3f errous oxide f erric oxide

6.

ReductionO pposite process o f oxidation; usually occurs in waterlogged (anaerobic)conditions in the absence o f f ree oxygen.R eduction o f iron to f errous, it more soluble and mobile, water is stainedbrown o f oxides.

Chemical weathering


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P roducts of weathering Primary Residual DissolvedMinerals Minerals Ions

Feldspar Clay minerals K +, Ca +2 , Na +Aluminum hydroxide

Fe-Mg minerals Hematite & Mg +2

Limonite

Quartz Quartz S ilica

Primary S olids that Ions that are carriedMinerals remain in soil away in water

----------Detrital sediments------------------ Chemical & biochemicalsediments


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W EATHERING PROCE SS ES


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W EATHERIN G P ROFILE

a) A schematic vertical sectionthrough a weathering profile

b) In reality, the weathering profile maybe more complex, result ing from structures in the rock mass.


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Geological ProcessesGeological ProcessesB) Exogenic Processes

Hydraulic action is the sweepingaway o f loose material by runningwater; the companion processper f ormed by wind is known asdeflation .T he action o f ice moving over a landsur f ace is sometimes calledscouring; plucking and gouging areerosional processes restricted toglaciers.


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lecture#10a geomorphology

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