Internal Forces of Change

Types of Boundaries  Convergent –Come together  Divergent –Pull apart  Transform –Slide past each other

Convergent Boundaries  Subduction –One plate dives beneath another –Forms volcanic mountains  Accretion –As one plate slides beneath another, a trench is formed –Overriding plate scrapes off the subducted plate, leveling off undersea mountains and ridges  Folding –Two continental plates collide, forming mountains

Divergent Boundaries  Spreading –Two sea plates pull apart –Magma rises, creating ridges or undersea mountain ranges (“new” land)

Transform Boundaries  Fault –Crack in earth’s surface where two plates can slide past one another –When plates make a sudden, violent shift, earthquake! odies/elearning/module04swf.swf nimations/ch2.htm#9

External Forces of Change

Weathering  Definition: The breaking down of rocks on the earth’s surface into smaller pieces.  Different from erosion!  No movement

Physical Weathering  Caused by heat, water, ice, or pressure

Frost Wedging

Frost Heaving

Plant Roots

Burrowing of Animals

Temperature Changes

Chemical Weathering Caused by chemical reactions.Caused by chemical reactions. Can be caused by water, carbon dioxide, oxygen, acid rainCan be caused by water, carbon dioxide, oxygen, acid rain 1908 to 1969 Acid rain has eaten away this limestone statue.

Water  Water weathers rock by dissolving it

Oxygen  Iron combines with oxygen in the presence of water in a processes called oxidation  The product of oxidation is rust

Acid Rain  Burning coal, oil and gas react chemically with water forming acids.  Acid rain causes very rapid chemical weathering

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Erosion  Definition: The process by which water, ice, wind or gravity moves pieces of rock and soil  Different from weathering!  Movement

 Caused by fast- moving water such as rain, rivers, streams and oceans. Can eventually form a canyon or cliff (ocean). –Ex. Grand Canyon Water Erosion

 Caused by the movement of dust, sand and soil. Can create loess, a fertile soil carried by wind. –Ex. Great Plains Wind Erosion

 Caused by large pieces of ice moving across the earth’s surface. Can leave behind moraines (large piles of rock and debris). –Ex. Rocky Mountains Glacial (Ice) Erosion

Glacial Erosion

Water Cycle  Constant movement of water on earth.  Evaporation, condensation, precipitation  Amount of water on earth really never changes!