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Deposition by Streams

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Erosion and Deposition by Water
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By Streams and Rivers

Source: Ian Sane https://www.flickr.com/photos/31246066@N04/8156546629/in/photolist-9zbjtp-bVJF32-cd6X4C-mNMtL-dr7NhW-5dE68C-5rxhtK-ndraB-dNhBNV-drnQ6D-4ccwWH-nCpt2-9XBTbA-jbZetj-87K8RN-dqLr9i-6m1Fd6-dnYvwE-dRy2Db-4aVGWK-5G9n4L-nyZpSk-h9Up1z-fwDQAN-heHhk3-a6DMhZ-4qNE2L-6irix4-ceUXjw-9Gywh1-8h6xKJ-CsBKc-6v3UhF-frWKw6-8qTRZj-bV8vJv-7Cf1J8-7UHJEF-2kUaN-8XBDMp-igFvdQ-fELWwe-hAYFuo-5KVJEW-48mR5P-kSg5QU-bAioCh-dhCU2a-8KFG9m-crbM4S
License: CC BY-NC 3.0

[Figure1]

Erosion

Water from runoff, streams, and rivers can all cause erosion and deposition.

Runoff is formed when the ground is unable to soak up water on the surface. Runoff causes more erosion when the land is bare because plants help keep soil in place. Why is runoff an important cause of erosion?

Streams and rivers erode sediment from their banks. How does the erosion shape the landscape? (Hint: not to be confused with the shape glaciers produce)

The extent of erosion by a stream depends on the velocity of the water.

  • As water slows, are larger or smaller particles deposited first?
  • On a sloped mountain, how does the velocity of the water due to the steep slope affect the shape of the stream bed?

Waterfalls form where a stream flows from an area of harder to softer rock because water erodes the softer rock more quickly, making the stream bed drop.

Slow rivers are generally on flatter ground, with their large curves, or meanders, and floodplains, or the broad, flat area on both sides of a river.

  • How are floodplains created?
  • How are oxbow lakes created?

For more help on erosion by streams, check out the reading.

Deposition

Sediment is carried by streams as:

  • dissolved load (Hint: to help you remember – dissolved loads consist of dissolved ions)
  • suspended load (Hint: relate its characteristics back to the letter "S" – solid sediments are suspended)
  • bed load (Hint: particles move along the stream bed.To remember the relative size of the particles – beds are pretty big, so larger sediment is carried as bed load)
    • saltation is the intermittent movement of bed load sediments

As a stream slows, it deposits sediments. Larger particles are dropped in steep areas, while smaller particles are dropped as the slope lessens.

Alluvial fans occur in arid regions. How are alluvial fans formed?

Deltas form when a stream or river empties into large body of still water. Helpful hint: the capital Greek letter delta (∆) looks like a triangle, and river deltas are triangular-shaped.

Floods occur when river water overflows, usually due to heavy rains. How do floods affect floodplains?

Flooding river form natural levees, or raised strips of sediment deposited close to water's edge because water deposits the biggest sediments first. Helpful hint: the word levee starts w/ "L," and levees are created by larger sediments and create raised edges or "lips" on a river.

For more information on deposition by streams, click here.

By Groundwater

         

License: CC BY-NC 3.0

Erosion

Groundwater is water in an underground rock or sediment layer. Groundwater creates landforms by dissolving away rock.

Caves are created by groundwater erosion. How exactly are caves formed?

The ceiling of a cave may collapse. Rock and soil will above sink into the ground, creating a sinkhole on the surface of the ground.

For more details on erosion by groundwater, check out the reading.

Deposition

Goundwater dissolves minerals and rocks into ions, which are deposited into different structures, like crystals, stalactites, and stalagmites. Sometimes, stalactites and stalagmites form a column if they join together.

Remember: the word stalactite has a 'C,' and stalactites are on the ceiling of a cave, while stalagmite has a 'G' and are on ground.

To read more about deposition by groundwater, click here.

By Waves

       

Erosion

Waves erode sediments from cliffs and shorelines, and sediment in the ocean erodes the shore. How does size of a wave affect erosion?

Wave refraction affects wave energy. What happens to wave energy in quiet water areas? In land that sticks into water?

The following landforms can be created by erosion by waves:

  • wave-cut cliffs - vertical walls of exposed rock
  • wave-cut platforms - level areas of rock above sea level
  • sea arches – form when waves erode both sides of a cliff, creating a hole in a cliff, or an arch
  • sea stacks – form when the top of a sea arch erodes, creating pillars or "stacks" of rock in the water

Sediment is transported in water if waves are powerful, and sediment eroded from cliffs near a shoreline is also transported.

Wave refraction occurs because waves approach the shore at an angle. How does a wave bend?

For more information on erosion by waves, click here.

Deposition

On a beach, sand is deposited, but waves erode the beach away.

Sediment can be transported by longshore currents, or a longshore drift. 

  • How does longshore drift moves sediment along the shore?
  • Where does deposition by waves occur?
  • How does the size of the sediment particles affect the deposition?

In relatively quiet areas along a shore, waves deposit sand, forming beaches.

Waves move sand from beaches on shore to bars of sand offshore as seasons change. In the summer, waves have lower energy, and in winter, there are higher energy waves. Where does sand go in each season?

A spit is a ridge of sand extending away from shore, and the end might hook around towards the quieter waters. Hint: to help you remember – when someone spits, the spit projects outwards from their mouth, just as how spits protrude.

Waves may deposit sediment to form sandbars and barrier islands. What is a natural barrier island? (Hint: Long Island is a developed barrier island) How do natural barrier islands help during storms?

For more information on deposition by waves, you can take a look at the reading.

Protecting shorelines

Erosion by waves can be damaging in developed shores. To try to protect beaches, several man-made structures can be applied:

  • breakwaters – artificial barriers used to cause waves to break before they reach the shore
  • groin – a wall of rocks or concrete
  • seawalls – built parallel to the shore on the shore

How do groins protect beaches?

What are the differences and similarities between breakwaters and seawalls?

To check your answers, look here.

Image Attributions

  1. [1]^ Source: Ian Sane https://www.flickr.com/photos/31246066@N04/8156546629/in/photolist-9zbjtp-bVJF32-cd6X4C-mNMtL-dr7NhW-5dE68C-5rxhtK-ndraB-dNhBNV-drnQ6D-4ccwWH-nCpt2-9XBTbA-jbZetj-87K8RN-dqLr9i-6m1Fd6-dnYvwE-dRy2Db-4aVGWK-5G9n4L-nyZpSk-h9Up1z-fwDQAN-heHhk3-a6DMhZ-4qNE2L-6irix4-ceUXjw-9Gywh1-8h6xKJ-CsBKc-6v3UhF-frWKw6-8qTRZj-bV8vJv-7Cf1J8-7UHJEF-2kUaN-8XBDMp-igFvdQ-fELWwe-hAYFuo-5KVJEW-48mR5P-kSg5QU-bAioCh-dhCU2a-8KFG9m-crbM4S; License: CC BY-NC 3.0
  2. [2]^ License: CC BY-NC 3.0

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