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

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

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.

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

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

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)

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).

Glacial Features

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.

Deposition by Mass Movement

~ The most recognizable feature of mass movement is a pile of sediment often found at the base of cliffs.

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.

Deposition by Wind