forces of change : destructive forces forces of change : destructive forces forces that wear away...

Forces of Change :Forces of Change :

Destructive ForcesDestructive Forces

Forces that wear Forces that wear away the Earth are away the Earth are destructive forces.destructive forces.

1

There are two types of destructive forces.

A. Weathering (p.115-120)

B. Erosion

2

I Destructive ForcesA. Weathering: The breaking up of rock

without removal of the pieces.

3

1. Mechanical

The physical breaking up of rock without chemically changing it into a new substance.

4

1. Mechanicala.)plant action;When the the root hairs of a

plant grow into the pores of a rock. As the root grows , it expands and breaks the rock.

5

1. Mechanical

b.)frost action(Ice wedging);

When water seeps into the pores of rock during the day and freezes at night.The frozen water expands and over time breaks the rock.

7

www.trp.dundee.ac.uk/~spitz/misc.html8

1. Mechanical c.) temperature change;

When a rock is heated during the day, it expands and at night, as it cools , it contracts. Over time this process breaks the rock.

9

Also called thermal expansion.

10

Abrasion (p.116)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

http://www.ergis.cz/krkonose/index.php?lang=en&menu=1&navid=170&search_filter=category=-4-%3Bsearch=true

wears away exposed rock

11

Pressure release (exfoliation p116)



http://en.wikipedia.org/wiki/File:GeologicalExfoliationOfGraniteRock.jpg

Exfoliation is the process of the rock breaking off in layers

12

2. ChemicalThe breaking up of rock by

chemically changing the elements that make it up into whole, new but weaker elements.

This causes the rock to crumble.

13

2. Chemical a.) oxidation;

When an element or compound in a rock combines with oxygen.

Most elements that oxidize become weaker.If any of the elements in the rock combine with oxygen, the rock breaks apart.

14

www.geographyjim.org/weathering.htm

www.americanbonanza.com/.../photo_gallery/

15

2. Chemical b.)compounds in water;

Minerals combine with water to form new compounds. These compounds expand over time causing the rock to break.

16

2. Chemical c.)carbonation;When carbon dioxide from the

atmosphere dissolves in water, it creates carbonic acid. This acid removes the minerals in the rock and forms new compounds called carbonates.

17

www.geographypages.co.uk/limgran.htm

Carbonic acid from acid rain has dissolved some of the limestoneand left cracks.

18

B. Erosion:(p. 142 - 170) The breaking up of rock

with removal of the pieces.

19

B. Erosion There are four agents of

erosion; 1. Gravity (p. 147 - 149) 2. Water (p. 150 - 161) 3. Wind (p.161 - 163) 4. Moving ice (p. 165 - 170)

20

GRAVITYA)Mass wasting

1. Rockfall-an individual rock slides downhill.2. Rockslide -many rocks slide together downhill.3. Mudflow- debris mixed with watermoves downhill.4. Slump- a slide of loose debris that moves as a single unit.5. Creep - mass of soil and rock move 1 -10 mm per year.

21

Rockfall



http://atlas.nrcan.gc.ca/site/english/maps/environment/naturalhazards/landslides/fig_2_land_rockfall.jpg/image_view

22

Rockslide



http://www.cbc.ca/canada/story/2008/08/01/f-newsweek.html

23



MUD

FLOW

24

Slump

http://www.geosci.usyd.edu.au/users/prey/ACSGT/EReports/eR.2003/GroupD/Report2/web%20pages/Listric_Faults.html

25

Creep





CREEP26

B. Erosion 2. Water erosion a.) mechanical

1.) running water carries particles of sand ,pebbles rocks and even boulders that wear away the surfaces that they come into contact with. This type of water erosion does not change the chemical make up of any of the particles.

27

Mechanical Water Erosion

Water erosion creates different land forms (p. 150 - 163).

Streams - small or large run downhill in a channel.

Drainage basins - area of land in which water drains into a stream and eventually into a lake or ocean.

Divide - A ridge from which water drains from one side or the other.

28



These streams drain an area called the drainage basin.

Locate the divides.

http://www.kidsgeo.com/geology-for-kids/0076-drainage-basins-

watersheds.php

29

Mechanical Water ErosionWater erosion creates different land forms.Valleys and canyons - p.152

V shaped in high mountains where water runs swiftly and cuts deep.

Wide valleys in low, flat land where water runs more slowly and flood waters

deposit silt creating large flood plains.

30



http://www.evans-politics.com/yellowstone.html

31



32

Mechanical Water ErosionWater erosion creates different land forms.Meanders p. 152- as streams or rivers enter flat land, they slow and begin to curve causing sediment to be dropped on the inside bank and eroding the outside bank.Oxbow lakes p. 152 - During a flood the meanders may cut a new path and cut off a meander leaving itAs a U-shaped body of water.

33



"Image courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center."

Astronaut Photography of Earth - Display RecordISS015-E-6477

34

Mechanical Water ErosionWater erosion creates different land forms.Alluvial fans p. 153- when water leaves sediment at the base of a mountain as it enters open space,it drops the sediment in a fan shaped feature.Delta p. 153 - when water leaves sediment at the mouth of a river as it enters open water such as an ocean, it drops the sediment in a fan shaped feature.

35



36



http://www.earthdesign.com/biahyperspectral/skokomish_delta.jpg

37

B. Erosion 2. Water; b.) chemical- p. 154

1.) running water that has carbonic acid in it will take away the calcium (calcite) in the surfaces that it comes into contact with and wash it away. This is how most caves are formed.

38

Chemical Water ErosionWater erosion creates different land forms.

Caverns p. 154- Caused by acidic water seeping into the ground and reaching the bedrock.This water can erode limestone within the rock and create huge caves called caverns.Sinkholes p. 155 - are formed when the top of a cavern has caved in.

39



http://skywalker.cochise.edu/wellerr/students/colossal-cave/cave.htm

40



http://studentloancenter.com/blog/index.php?entryid=225

41

Waves Waves and currents shape shorelines p.158- 159

Longshore drift- the zigzag motion of sand along a beach causes the beach to erode in one area and be built up in others.

Longshore current - the movement of water along a shore. Usually, this movement is at an angel and the angel changes depending on the direction of the waves.This erodes beaches.

42

Waves Waves and currents shape shorelines p.160

Sandbars - a ridge of sand built up under water by the action of currents and waves.

barrier island - a ridge of sand built up above water by the action of currents and waves.

43



http://www.australiaadventures.com/pictures.htm

44



http://geology.rockbandit.net/2008/09/15/how-barrier-islands-such-as-galveston-work/

45

B. Erosion 1.Wind; When wind storms blow sand and dust at other

rocks , the particles wear away the rocks or other surfaces that they hit. Other particles break off and they too are carried by the wind to other places.

Wind erosion forms; 161 -163 Dunes Loess deposits Desert pavement

46



http://projects.math.arizona.edu/~sp2007/sdgroup.html

47



http://www.pbase.com/dougsherman/image/94997414

48



http://z.about.com/d/geology/1/0/q/O/1/paveblythecloseup.jpg

49

B. Erosion Moving ice; p. 165 - 170is called a glacier. A glacier cancarve deep, wide valleys and move hugeamounts of land to other places.Glaciers deposits are called till.Types of till include; moraines. drumlins kettle lakes.

50

Alpine Glacial valley

51



http://formontana.net/moraine.html

Postcard Photo by Lawrence Dodge of Big Sky Magic Enterprises

52



http://oz.plymouth.edu/~sci_ed/Turski/Courses/Earth_Science/Images/4.drumlin.jpg

53



http://www.physicalgeography.net/fundamentals/10af.html

54