Forces of Change : Destructive Forces Forces of Change : Destructive Forces Forces that wear away the Earth are destructive forces. 1

There are two types of destructive forces. o A. Weathering (p ) o B. Erosion 2

I Destructive Forces o A. 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. Mechanical o a.)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

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1. Mechanical o 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

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1. Mechanical o 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) 170&search_filter=category=-4-%3Bsearch=true wears away exposed rock 11

Pressure release (exfoliation p116) Exfoliation is the process of the rock breaking off in layers 12

2. Chemical The 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 o 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

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2. Chemical o 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 o 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

Carbonic acid from acid rain has dissolved some of the limestone and left cracks. 18

o B. Erosion:(p ) The breaking up of rock with removal of the pieces. 19

B. Erosion o There are four agents of erosion; o 1. Gravity (p ) o 2. Water (p ) o 3. Wind (p ) o 4. Moving ice (p ) 20

GRAVITY A)Mass wasting 1. Rockfall-an individual rock slides downhill. 2. Rockslide -many rocks slide together downhill. 3. Mudflow- debris mixed with water moves downhill. 4. Slump- a slide of loose debris that moves as a single unit. 5. Creep - mass of soil and rock move mm per year. 21

Rockfall naturalhazards/landslides/fig_2_land_rockfall.jpg/image_view 22

Rockslide 23

MUDMUD FLOWFLOW 24

Slump /GroupD/Report2/web%20pages/Listric_Faults.html 25

Creep CREEP 26

B. Erosion o 2. Water erosion o a.) mechanical o 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 o Water erosion creates different land forms (p ). o Streams - small or large run downhill in a channel. o Drainage basins - area of land in which water drains into a stream and eventually into a lake or ocean. o 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. watersheds.php 29

Mechanical Water Erosion o Water erosion creates different land forms. o 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

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Mechanical Water Erosion o Water erosion creates different land forms. Meanders p 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 During a flood the meanders may cut a new path and cut off a meander leaving it As a U-shaped body of water. 33

"Image courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center." Astronaut Photography of Earth - Display Record ISS015-E

Mechanical Water Erosion o Water erosion creates different land forms. Alluvial fans p 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 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

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B. Erosion o 2. Water; o b.) chemical- p. 154 o 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 Erosion o Water erosion creates different land forms. Caverns p 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 are formed when the top of a cavern has caved in. 39

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Waves Waves and currents shape shorelines p 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

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B. Erosion o 1.Wind; o 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. o Wind erosion forms; o Dunes o Loess deposits o Desert pavement 46

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B. Erosion o Moving ice; p is called a glacier. A glacier can carve deep, wide valleys and move huge amounts of land to other places. Glaciers deposits are called till. Types of till include; o moraines. o drumlins o kettle lakes. 50

Alpine Glacial valley 51

Postcard Photo by Lawrence Dodge of Big Sky Magic Enterprises 52

Images/4.drumlin.jpg 53

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