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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
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
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
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
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
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