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Erosion and Deposition
Erosion- process that moves weathered sediments
from one place to another
Deposition- the dropping of sediments that have
been eroded
Erosion and deposition are two parts of the same
process.
Erosion only occurs when there is enough
energy to carry the sediments. Deposition occurs
when the energy decreases.
There are four main forces that cause
erosion and deposition:
1. Gravity
2. Running Water
3. Glaciers
4. Wind
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I. Gravity
“mass movement”
A. slump - on steep slopes; material weakens
Underneath; ex.- a pile of sediments at the bottom
of a hill, with an
indentation in the hill
B. creep - sediments move s-l-o-w-l-y
downhill; caused by repeated freezing
and thawing; ex. - a slanted fence
C. Rockslides - rocks break loose and tumble
to the bottom of the hill; ex.- piles of rocks
D. Mudflows - happens in relatively dry areas
when a thick layer of sediments mixes with water,
becomes heavy and pasty, slides downhill
II. Running Water
A. Rill/Gully Erosion - “scar” left after water has run
downhill; rills are small, gullies larger and more
Permanent
B. Sheet Erosion - happens in a flat area after it rains
C. In Streams - moving water constantly picks
up and carries sediments as it moves; deposition at
mouth of river
Alluvial fan - triangular area of deposition
in a river or stream (much like a sandbar)
Delta - an alluvial fan that occurs at the mouth
of a river or stream
III. Glaciers - masses of moving ice and snow
A. Valley glaciers - smaller; more common
B. Continental glaciers - huge; in polar regions
Glacial Erosion - glaciers act like bulldozers;
carry away a lot of material and wear down rocks;
Striations - scrapes left on rock from a glacier;
Rocks stuck in ice abrade rock beneath it
*** Glacial valleys are U-shaped, as opposed to
V-shaped valleys formed by streams.
Glacial Deposition - occurs when ice begins to melt;
Sediments deposited
Till - glacial deposit made up of a jumble of different
Sized rocks
Outwash - and and gravel that is released in the
meltwater
IV. Wind
Deflation - small sediment such as sand are picked
Up and carried away
Abrasion - wind carried sediments act like sandpaper
Deposition occurs near supportive backgrounds
Loess - thick deposits of fine wind-eroded
materials