Deposition

Deposition

When transported material settles or comes to rest

Caused by: running water, glacial ice, waves, or wind losing energy so they can no longer transport the material

Sediment deposits around Britain

Deposition also refers to accumulation of chemical or organic sediments (example: shells) on the sea floor. Organisms die and their remains may

acccumulate Salt crystals may be left behind

when salt water evaporates

Where it may occur: Deep sea floor, desert valley, river

channel, coral reef, lake bottom, beach, sand dune

Each environment is different Geoscientist study sedimentary rocks

to determine what the environment was originally like when the sedimentary rock formed

Running Water

Rivers Most rivers meander. The river is still eroding its banks along

the outsides, where water flow is fastest. On the insides of bends, where flow is

slow, it deposits sand and gravel making the meanders become larger.

When the river floods, it flows out across the floodplain and slows down, depositing finer silt and mud. This forms fertile farmland.

When rivers meet the sea When rivers meet the sea they can form

estuaries As the current slows down, sand and gravel

are deposited to form sandbanks. The sandbanks are also re-arranged by tides

near the river mouth.  The finest material, mostly mud, may settle

out to form mudflats or be carried further out to sea where it finally settles out in calmer water.

 

Glaciers

Glaciers

Unsorted, unlayered rock debris carried and left by glaciers is called till

A moraine is a body of till carried on a glacier or left behind after a glacier recedes

Moraines

Lateral moraines are low ridgeline piles of till along the side of a glacier

Medial moraines are a single line of till on a glacier formed by adjacent lateral moraines joining and being carried down a glacier

See fig. 16.25, 16.26

An end moraine is a ridge of glacial debris that piles up along the front edge of the ice

Two types: terminal and recessional Terminal: end moraine that shows the

farthest point of where the glacier advanced Recessional: end moraine built when the

end of a receding glacier remains temporarily stationary

Erratic

An erratic is an ice-transported boulder that has been transported from elsewhere

Outwash

Material deposited by debris-laden meltwater is called outwash

Has layers and is sorted Usually consists of sand and

gravel, and is used for aggregate to build roads and to mix with cement to make concrete

Wind

Loess

Deposit of wind-blown silt and clay High porosity May be found downwind of a

source of fine sediment, such as a desert or an area with glacial outwash

Sand Dunes Mounds of loose sand grains that

are piled by the wind Most likely to be in areas with

strong winds that blow in the same direction

Found in the Sahara Desert, beach dunes such as Lake Athabasca where dunes may be 30m high and 100s of meters long

Mineral composition of sand grains in sand dunes depends on the original source and how much chemical weathering is occurring

Beaches in humid regions have a high percentage of quartz as it is more resistant to chemical weathering

Sand grains tend to be well sorted Find-grained silt and clay can be

transported further than sand Anything coarser than sand will be

left behind If grass or other vegetation occurs

there, movement will stop (stabilized)

When sand moves over a dune surface you will find wind ripples Small, low ridges of sand Sand moves perpendicular to the

ripples so you can determine the direction of sand movement

Waves Transportation by waves and currents moves

rock particles eroded from one part of a coastline to a different place for deposition

Many kinds of depositional landforms are possible

depends on the configuration of the original coastline, direction of sediment transport, nature of the waves, and shape and steepness of the offshore underwater slope.

Some common depositional forms are spits, barrier beaches or bay-mouth bars, tombolos