Download Chapter Seven: Erosion

Chapter Eight: Erosion
I. Erosion & Deposition
A. Erosion
1. wears away surface materials and moves them from one location to
another
2. Agents (causes) of Erosion
a) gravity
b) glaciers
c) wind
d) water
B. Deposition
1. the more quickly an agent of erosion is moving the more sediments it
can carry
2. All agents of erosion drop their load of sediments when their energy of
motion decreases (slows down)
II. Gravity
A. def. force of attraction that exists between all objects
B. Mass Movement
1. Gravity alone causes loose materials to move downhill
C. Examples of Mass Movement
1. Slump
a) mass movement in which loose materials or rock layers slip
down a slope
b) strong rock lies over weak materials
c) the weak material can not hold the rock up so it slides downhill
d) will leave a curved “scar” where the slumped materials
originally rested
e) happens mostly after earthquakes or heavy rains
2. Creep
a) sediments slowly inch their way down a hill
b) common in areas of freezing & thawing
3. Rockslides
a) large blocks of rock break loose & start tumbling
b) while falling these rocks crash into other rocks causing them to
break loose and fall
c) more & more rocks break loose & tumble to the bottom
d) rockslides are very fast & destructive. Can happen at any time
without warning
4. Mudflows
a) usually happen in dry areas where weathering accumulates thick
layers of sediment
b) when heavy rains fall the water mixes with the dry sediments
c) gravity then causes the water & the sediments to move downhill
1
d) when a mudflow reaches the bottom of a slope it loses energy &
deposits its sediments
e) the sediments usually spread out into a cone shape
III. Glaciers
A. def. a moving mass of ice & snow
1. Form in an area where the snow never melts
2. the snow begins piling up into a thick layer
3. Eventually this thick layer of ice moves & becomes a glacier
B. Continental Glaciers
1. Huge masses of ice & snow
2. Ice Age
a) 20,000 years ago continental glaciers covered 28% of the Earth
3. Today are found at the polar regions and Greenland
a) only cover 10% of the Earth
4. These glaciers are so thick they can almost bury mountain ranges
C. Valley Glaciers
1. Found on mountains where snow does not melt in the summer
2. Form & Grow in the valleys and slide down the mountain
3. Have U-shaped valleys unlike streams that have V-shaped valleys
D. Glacial Erosion
1. Glaciers behave like huge bulldozers
a) they push along anything loose that is in front of, underneath or
beside the glacier
2. Plucking
a) boulders, gravel, & sand are broken loose by ice wedging.
b) this loose material is then dragged along by a glacier
3. Striations
a) long, deep, parallel grooves in the rock underneath the glacier
b) are caused by boulders, sand, & gravel being dragged
underneath the glacier
E. Evidence of Valley Glaciers
1. Cirque
a) valley glaciers erode a bowl shaped basin in the sides of
mountains
2. Arête
a) 2 or more glaciers have eroded a mountain summit to form a
sharpened peak
b) these sharpened peaks are called horns
c) Ex. Materhorn, Swiss Alps
2
3. U-shaped Valleys
a) as a valley glacier moves along it carves the valley out into a Ushape
4. Kettle Lakes
a) lakes formed when huge blocks of ice melt
F. Glacial Deposition
1. Till
a) a mixture of different sized sediments
b) includes silt, clay, sand, and boulders
2. Moraine
a) a large pile of material that is piled up and left by a moving
glacier
b) terminal moraine: a ridge of material at the end of a glacier
c) lateral moraine: a ridge of material at the sides of a glacier
d) medial moraine: a ridge of material in the middle of glaciers
3. Outwash
a) material deposited by melt water of a glacier
b) heavier sediments are deposited closer to a glacier while smaller
ones move farther away.
c) esker: a winding ridge of sand & gravel deposited in tunnels
beneath a glacier
d) outwash plain: flat areas of deposited materials in front of a
retreating (melting) glacier
4. Erratics
a) large rock fragments deposited by a glacier
b) some erratics have been transported hundreds of miles from its
source
IV. Wind Erosion
A. Deflation
1. Wind blows across loose sediments such as clay, silt, & sand and picks
them up
2. After these sediments are removed only the larger, coarser ones remain
3. The coarse material left behind is called desert pavement
B. Abrasion
1. wind picks up loose silt, clay, & sand sized sediments
2. the sediments are blown into rocks or buildings
3. the force of these sediments breaks down and erodes the rock
(sandblasting)
4. ventifacts: rocks shaped by wind erosion
C. Sandstorms
1. strong winds blow sand off the ground
2. as the sand grains blow along they collide with other sand grains
3
causing them to rise off the ground
3. Most sandstorms occur in the desert
D. Dust Storms
1. When a drought occurs the wind can easily pick up soil
2. Most soil particles are smaller than sand and are easily picked up
3. Dust Storms can cause these particles to be carried great distances
a) 1930’s soil from Kansas was carried to Maine
E. Reducing Wind Erosion
1. Windbreaks
a) farmers plant trees to stop the wind
b) the trees and their roots help to hold the soil in place
2. Roots
a) farmers plant cover crops to hold the soil down
b) the deeper the root system the better it holds down soil
c) planting vegetation is a good way to reduce the affects of
deflation & abrasion
F. Deposition by Wind
1. Loess
a) fine grained wind deposits
b) the location loess is deposited forms fertile farmlands
c) loess deposits in the USA were formed mainly from glacial
outwash plains.
2. Dunes
a) a mound of sand drifted by wind
b) formed in places where there is sand and the wind blows daily
c) can grow 50 to 180 meters high
d) forms in areas of beaches, barrier islands, & deserts
3. Dune Migration
a) sand dunes move with the wind
b) windward side – side facing the wind
c) leeward side- side facing away from the wind
d) dunes move from the windward side towards the leeward side
*You must also know your vocabulary
* The test will contain several application style questions.
*There will be some open-ended questions also for completion (these are worth more)
4