1. Erosion and Deposition
Chapter 9

2. Chapter 9 – Erosion and Deposition
Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface.

3. Chapter 9 – Erosion and Deposition
Erosion is the movement of pieces of rock and other materials (sediment) on Earth’s surface.
Can be caused by gravity, running water, glaciers, waves or wind.

4. Chapter 9 – Erosion and Deposition
Most sediment comes from weathering.
Weathering is the breakdown of rock and other materials at Earth’s surface.

5. Chapter 9 – Erosion and Deposition
Deposition happens when sediment is dropped.
Dropped sediment can build up over time and make new landforms.

6. Chapter 9 – Erosion and Deposition
Mass movement is any process that moves sediment downhill.
Caused by gravity.
Different types of mass movement include landslides, mudflows, slump and creep.

7. Chapter 9 – Erosion and Deposition
Landslides happen when rocks and soil quickly slide down a steep slope.
Mudflows happen when rocks and mud quickly slide down a steep slope.

8. Chapter 9 – Erosion and Deposition
Slump happens when a mass of rocks and soil suddenly slides down a steep slope.
Slump is different than a landslide.
The material in slump moves down the slope in one large mass.

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Creep happens when rocks and soil move very slowly down a hill.
Creep can happen even on gentle slopes.

10. Chapter 9 – Erosion and Deposition
Moving water is the major cause of the erosion that has shaped Earth’s land surface.
Runoff (rainfall that does not soak in but runs over the ground) forms tiny grooves in the soil called rills, which flow together to form bigger grooves called gullies which join together to form streams which join together to form rivers.
A tributary is a stream or river that flows into a bigger river.

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12. Chapter 9 – Erosion and Deposition
A river on a steep slope flows straight & fast. This is usually at the origin or beginning of the river. Forms a V-shaped valley as it flows.
A river toward the end flows slow on a gentle slope with more curves (meanders). Forms a wide, flat valley.

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When a river flows from hard rock to soft rock, the soft rock wears away faster than the hard rock, this forms a waterfall.

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A meander is a big bend in a river which forms in a flood plain.
An oxbow lake is a meander that has been cut off from a river and is curved like a meander.

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When rivers slow down as they leave mountains, flow into lakes or oceans, or flood their banks, they drop sediment, called a deposit.
An alluvial fan is a deposit that forms where a river leaves a mountain range.

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A delta is a deposit that forms where a river flows into a lake or ocean.

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When a river floods, it drops sediment on its flood plain which results in flood plain soil being thick and fertile.

19. Chapter 9 – Erosion and Deposition
Groundwater (water that sinks into the ground) can cause erosion when it mixes with carbon dioxide to become a weak acid and can dissolve limestone and make holes in the rock.
Big holes in limestone are called caves.
If the roof of a cave wears away, the land over it can sink in making a hole in the ground called a sink hole.

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Groundwater can drip from the roof of a cave and form deposits that look like icicles.
Deposits that hang down from the roof of a cave are stalactites, while deposits that stick up from the floor are called stalagmites.

21. Chapter 9 – Erosion and Deposition
Moving water has energy.
As water goes down a slope, potential energy changes into kinetic energy.
A river erodes Earth’s surface by picking up and moving sediment.
Most sediment washes or falls into a river as a result of mass movement (landslides for example) and runoff.

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A river can get sediment through the process of abrasion.
Abrasion occurs when sediment in the water scrapes against the bottom and sides of the river and chips away bits of rock.
Sediment moves downstream with the water.

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A river’s slope, volume of flow, and the shape of its streambed all affect how fast the river flows and how much sediment it can erode.
High volume = fast speed
Narrow, deep channel = fast speed
Steep slope = fast speed

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A big river with a lot of water can carry more sediment and larger pieces than a small river.
Big rocks in a streambed can make water rough which wears away the streambed faster than smooth water.

25. Chapter 9 – Erosion and Deposition
Where a river curves, water moves faster along the outside of the curve and slower on the inside of the curve.
Faster water wears away the outside bank and slower water drops sediment along the inside bank.

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A glacier is a huge chunk of ice that moves over the land and forms when snow and ice build up year after year because more snow falls than melts.

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A continental glacier covers all or most of a continent, it moves very slowly in all directions.
When continental glaciers cover much of Earth’s surface, it is called an ice age.
A valley glacier is a long, narrow glacier in a mountain valley which moves only down the valley and can move faster than a continental glacier.

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As a glacier moves, it erodes the land under it.
Two processes by which glaciers erode the land are plucking and abrasion.
Plucking: as a glacier flows over land it picks up rocks.

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Abrasion: As the glacier moves, the sediment on the bottom scrapes the land.
Abrasion can make valleys wider and can scrape away mountainsides leaving a small mountain peak called a horn.

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When a glacier melts, it deposits the sediment it eroded from the land, called till.
A moraine is a ridge or mound that forms where till is dropped along the edge of a glacier.
Sometimes a glacier drops a big chunk of ice instead of rock or soil, when the ice melts, it leaves a low spot in the ground called a kettle.

33. Glacial Landforms

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When ocean wind touches ocean water, energy passes from the wind to the water which causes waves, which in turn carry energy across the ocean.

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Waves shape the coast through erosion by breaking down rock and transporting sand and other sediment which can wear away rock by abrasion when it hits the shore.
Some rock on shore is harder than the rock around it and wears away slower. This forms a headland which is part of a shore that sticks out into the ocean.
Waves can wear away the bottoms of cliffs along the shore
Waves can wear away holes in cliffs and form caves.

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Waves shape a coast when they deposit sediment, forming coastal features such as beaches, spits, and barrier beaches.
These form when waves slow down at a coast and drop sediment which can build up to make different landforms.
A beach is an area of sediment at the edge of the water, usually sand.

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A longshore drift occurs when waves hit a beach at an angle and carry sand down the beach.

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A spit is a beach that sticks out into the water like a finger and forms when a headland stops longshore drift, and the sand piles up.

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When waves drop sand in a long ridge parallel to shore, a sandbar is formed.
If the sand builds up above the surface of the water it forms a narrow island called a barrier beach.

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Wind causes erosion by deflation and abrasion.
Deflation is the process by which wind removes surface materials (sediment)
The stronger the wind, the bigger the pieces of sediment the wind can pick up.
The blowing sediment scrubs and polishes rock in a process called abrasion.

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42. Chapter 9 – Erosion and Deposition
Wind erosion and deposition may form sand dunes and loess deposits.
Wind drops the sediment it is carrying when a wall or other barrier slows the wind.

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Sand dunes are ridges or mounds that form when the wind drops sand. Sand dunes can be small or large.

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Loess is tiny pieces of sediment that are dropped by the wind. Loess helps make soil fertile.
There are big loess deposits in states such as Nebraska and Iowa.