Download Changes on the earth*s surface

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CHANGES ON THE
EARTH’S SURFACE
I. WEATHERING
A. Weathering – breakdown of rock at or near the
earth’s surface into smaller and smaller pieces
B. Mechanical Weathering – occurs when rock is actually
broken or weakened physically
1. breaks large masses of rock into smaller pieces (boulders,
stones, pebbles, sand, silt, and dust)
C. Chemical Weathering – alters a rock’s chemical makeup by
changing the minerals that form the rock or combining them with
new chemicals
1. can change one rock into a completely different type of rock
2. many caves are formed when acidic water seeps into cracks of
rocks
3. acid rain – chemicals in the polluted air combine with water
vapor and fall back to earth (destroys forests, pollutes water, eats
away at stone buildings)
EXAMPLES
Mechanical
Weathering
Chemical
Weathering
II. EROSION
A. Erosion – movement of weathered materials such as
gravel, soil, and sand
B. 3 most common causes of erosion:
1. water
2. wind
3. glaciers
C. Important part of the cycle that has made and kept
the earth a place where living things can survive
A. WATER
1. Water is the greatest cause of erosion, because over time,
water can cut into the hardest rock and wear it away
2. Water moving down a streambed carries sediment (small
particles of soil, sand, and gravel)…that sediment helps grind
away the surface of rocks
3. The rock and soil that is carried away with
erosion eventually creates other landforms
4. The Mississippi River carries approximately
159 million tons of sediment a year
5. Crashing ocean surf causes steep bluffs,
cliffs, or sand dunes
B. WIND
1. Cause of erosion in areas where there is little water and few
plants to hold the soil in place
2. In the Great Plains, the rich fertile soil that they once had was
blown away by the wind during a drought…this area is now
known as the “Dust Bowl” because they cannot grow
anything there anymore
3. The wind can also deposit mineral-rich dust and silt called
loess, which can help areas that once were barren
4. Sandstorms can cause erosion by carving or smoothing the
surfaces of rock formations and man-made objects
C. GLACIERS
1. Glaciers – huge, slow-moving sheets of ice
2. Form over many years as layers of unmelted snow are pressed
together, thaw slightly, and then turn to ice
3. As glaciers move, they carry dirt, rocks, and boulders
4. The time periods where much of the earth is covered in glaciers
are known as Ice Ages – geologists believe that we’ve had at least
4
5. Much of the U.S. was formed by glaciers (Great Lakes, Long
Island, etc.)
6. Glaciers slide forward because of how heavy they are and only
pieces of it move at a time (oozes)
GLACIERS