Download - Topic10: Deposition
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Topic10:Deposition
Deposition = the process by which sediments are released, settled from or dropped from an erosional system.
**Deposition usually occurs when the velocity or speed of any erosional system decreases or stops moving**
ex: A stream slowing down
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Rate of Deposition The faster a stream flows, the larger the size
sediments it can carry. ESRT chart pg. 6
Larger sediments settle out faster, they tend to be heavier and sink faster
The more rounded a sediment, the faster it will settle
The larger the density, the faster it will settle
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Sorting of sediments and deposition
When a mixture of sediment sizes in water settle out rapidly, a horizontal bed or layer develops. The sediment size will decrease from the bottom to the top. This is called graded bedding.
In a delta, the larger, denser and more rounded sediments will settle first.
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Glacial and Mass Movement Deposits
In a glacier and mass movements, sediments of all sizes, shapes and densities are deposited together. This will produce a unsorted un-layered deposit
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Dynamic Equilibrium if an Erosional System
Since all sediments picked up by the stream during erosion must eventually be deposited, the system is said to be in dynamic equilibrium.
Meaning: Rate of erosion = Rate of
deposition
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Features produced by deposition of a Stream
~ In a stream itself, deposition occurs on the inside of meanders, where the velocity is low.
~ When a stream overflows, sediments form levees at the edge of the river. Sediments also spread out in the floodplain
~ If the stream changes its path, you can have a meander or bend that is cut off, creating a curved lake (oxbow lake)
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Features produced by deposition of a Glacier
~ At the end of a glacier, sediments are dropped in unsorted sheets called a moraine.
~ If sediment deposits at the bottom of a glacier, it tends to be a low, long, narrow, streamlined oval mound. This is called a drumlin.
~ When a block of ice is left behind and melts it forms a depression called a kettle. When they get filled with water, it is called a kettle lake.
~ As a glacier melts, running water will produce a sorted deposit called a outwash plain (broad delta like feature).
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Glacial Features
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Deposition on Coastlines by waves and currents
~Wave movement towards the shore builds up sediment at the coastline, called a beach.
~ If a sandbar rises above sea level, vegetation can stabilize and grow, creating a barrier
island.
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Deposition by Mass Movement
~ The most recognizable feature of mass movement is a pile of sediment often found at the base of cliffs.
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Deposition by Wind When wind slows down or stops blowing,
sediments are dropped-but these particles are typically smaller than sand.
Particles smaller than sand are usually categorized as dust. Much of the dust is deposited over a large expansive area.
Sand particles are deposited in layers or mounds called sand dunes. Sand dunes typically have a gentle slope on the windward side and a steep slope on the leeward side. They will “migrate” in the direction of the wind creating layers of sloping sorted sediment that is cross-bedded.
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Deposition by Wind