Erosion and Deposition

Erosion- process that moves weathered sedimentsfrom one place to another

Deposition- the dropping of sediments that havebeen 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 causeerosion 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 weakensUnderneath; 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-ydownhill; caused by repeated freezingand thawing; ex. - a slanted fence

C. Rockslides - rocks break loose and tumbleto the bottom of the hill; ex.- piles of rocks

D. Mudflows - happens in relatively dry areaswhen 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 rundownhill; 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 picksup and carries sediments as it moves; deposition at

mouth of river

Alluvial fan - triangular area of depositionin a river or stream (much like a sandbar)

Delta - an alluvial fan that occurs at the mouthof 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 differentSized rocks

Outwash - and and gravel that is released in themeltwater

IV. Wind

Deflation - small sediment such as sand are pickedUp and carried away

Abrasion - wind carried sediments act like sandpaper

Deposition occurs near supportive backgrounds

Loess - thick deposits of fine wind-erodedmaterials