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EROSION OF EARTH’S SURFACE
Do Now: Explain two types of weathering.
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What is Erosion?
• The wearing away and removal of rock or sediment
• Because of gravity, ice, water, and wind.
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1. Gravity
• Gravity: Force that pulls every object toward an object’s center.
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• Mass Movement: When gravity alone causes rock or sediment to move down a slope
• Can occur ANYWHERE there are hills, mountains, or Volcanoes
• 4 types: creep, slump, rock slides, mudflows
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A. Creep
• The process in which sediments move SLOWLY down hill.
• Common with freezing and thawing.
• As ice EXPANDS in soil, it pushes sediments up. As ice THAWS in soil, the
sediments move further down the slope.
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B. Slump
• Occurs when a mass of rock or sediment moves down hill leaving a curved scar
• Most common:
• 1. thick layers of loose sediment
• 2. sedimentary rock.
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C. Rock Slides
• Layers of rock break loose from slopes and slide to the bottom.
• Rock layers often bounce and break apart during movement. This produces a huge,
jumbled pile of rocks at the bottom of the slope.
• They are DESTRUCTIVE, destroying villages or causing hazards on roads in
mountainous areas.
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D. Mudflows
• Where heavy rains or melting snow and ice saturate sediments, mudflows can
develop
• Mudflow: Mass of wet sediment that flows downhill over the ground surface.
• Mudflows can move fast or slow, depending on where they are found
• On volcanoes= move FAST
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2. Ice
• In cold regions, large masses of ice can accumulate to form GLACIERS.
• When a glacier becomes big enough, its own weight causes it to flow downhill due to
gravity.
• As glaciers move, they erode Earth’s surface.
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Glaciers
• Two types:
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2. Ice
• In cold regions, large masses of ice can accumulate to form GLACIERS.
• When a glacier becomes big enough, its own weight causes it to flow downhill due to
gravity.
• As glaciers move, they erode Earth’s surface.
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Glaciers
• Two types:
• Continental Glaciers
• cover about 10% of the Earth. They are SO large, they can bury mountain
ranges.
• Valley Glaciers
• Smaller, located on high mountains
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Glacial Erosion
• Glaciers can erode rock in two ways:
• 1. if the underlying rock has cracks in it, the ice can pull out pieces of rock.
• This works SLOWLY
• 2. Scratching of the rock’s surface by the rocks that are stuck in the glacier.
• As different sized fragments of rock are dragged along as the glacier move, and
they act like sandpaper to the rock below it
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Effects of Glacial Erosion
• In mountains, valley glaciers can remove rock from the mountaintops to form large
bowls, called Circues, and steep peaks
• In Valleys, the glaciers erode the rock on the valley sides causing a wider U-shaped
valley.
• For Continental Glaciers, they can scour large lakes and completely remove rock
layers from Earth’s surface.
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Glacial Deposition
• Glaciers also can deposit sediments
• When stagnant glacier ice melts, the sediment the ice was carrying gets left behind
on Earth’s surface.
• This sediment that gets left behind is called till.
• Till is a mixture of different sized particles, from clay to large boulders.
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• During summer, when the glaciers melt, they can produce streams of water. These
streams can carry and deposit sediment.
• When this happens, this is called outwash (NOT till).
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3. Wind
• Deflation: Erosion of land by Wind
• When wind blows across loose sediments like silt and sand, it lifts and carries it.
This erosion often leaves particles too heavy to move.
• Abrasion: erosion that can make pits in rocks and produce smooth, polished surfaces.
• Common in deserts and in regions with strong winds.
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• When wind blows around a rock, it slows down. This is what causes sand to be
deposited. If this keeps happening, a sand dune.
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4. Water
• Water that flows over Earth’s surface is called runoff
• If the water is moving fast, it can carry more material and erode earth’s surface
faster.
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• Common in deserts and in regions with strong winds.
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• When wind blows around a rock, it slows down. This is what causes sand to be
deposited. If this keeps happening, a sand dune.
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4. Water
• Water that flows over Earth’s surface is called runoff
• If the water is moving fast, it can carry more material and erode earth’s surface
faster.
• Sheet flow, rills and gullies, and streams
A. Sheet flow:
• When water flows downhill as a thin sheet
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B. Rills and Gullies
• Where a sheet of water flows around obstacles and becomes deeper, rills can form.
• Rills are small channels cut into the sediment at the Earth’s surface
• As the sediment flows through rills, the channels can get wider and deeper.
• When the channels get to be 0.5m across, they are called gullies
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C. Streams
• Gullies often connect to stream channels
• Most streams have water flowing through them continuously, others only have
water flowing during rainfall
• In the Mountains, streams flow down steep slopes. They get a lot of energy and
often cut into the rock beneath their valleys.
• White water rapids
• Waterfalls
• The speed of these streams causes erosion.
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