EROSION & DEPOSITION

What is erosion?

-Erosion is the removal of rock particles and soil from an area

-Erosion requires energy (usually supplied by gravity)

There are 4 distinct agents of erosion

-Rivers/streams-Glaciers-Wind-Wave Action

Transport of Sediments in Streams

-Sediment transport is dependent on 2 variables:

-Velocity (speed) of water-Particle Size

*Shape and density are of some importance

Particle Size

-Rock Particles are categorized into 6 types:

-Boulders-Cobbles-Pebbles-Sand-Silt-Clay

*Dissolved minerals are also transported

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Quantified Sediment Sizes

Sediment Transport Chart

-In general, the chart shows that larger particles require an increased water velocity (speed) to be transported

-If water velocity falls below that level, sediment is deposited on the bottom of the river

Water Velocity and Stream Morphology

-Water velocity is not a constant along a river nor is it constant across a transect

Water Velocity and Stream Morphology

-Because this is true, rivers have different channel shapes

-In a straight line path, rivers are fastest in the middle, leaving a channel deepest in the center

-As river water enters a curve, the faster water is on the outside causing more erosion and a greater depth

Stream Meanders

-As water slows on the inside bend of a meander sediments are deposited in a process called

deposition

-Erosion takes place on the outside of a curve; particles are removed by the faster water

-The meanders will look like this

Sorting of Sediments

-Faster moving water removes smaller sediments

-Therefore, a stream bottom will have larger particles on the bottom in faster moving water and smaller particles on the bottom in slower moving water

-Streams result in sorted sediments based on water velocity

Streams Entering Lakes

-The stream flow slows and the largest sediments are deposited first

Stream Valley Shape

-As streams downcut through soil and bedrock, they create a V-shaped valley

Glaciers

-Glaciers form when repeated snowfall accumulates in an area and forms into an ice

pack that is able to flow

Types of Glaciers

-For our purposes, there are 2 types of glaciers:

-Continental (Ice sheet): Spans all or some of a continent

-Valley (Alpine): Restricted to a valley

Glacial Presence in NYS

-A massive glacier covered New York (most recently around 10,000 years ago), and it is important to

understand how it shaped landforms in the area

Glacial Weathering

-Abrasion is the dominant form of weathering

underneath a glacier

-Rocks and other sediment are ground against bedrock as they are dragged

overhead

-Evidence: We find parallel grooves, called striations, in bedrock

Glacial Erosion

-As glaciers erode a landscape, they leave evidence of having been there

-Valleys take on a “U” shape

Finger Lakes

-Glacial erosion can leave behind a variety of observable features

-Finger Lakes are carved out of bedrock in the

direction that the glacier moved

Drumlins

-Elongated hills called drumlins are also found in areas that have

undergone glaciation

-The drumlins align with the direction of glacial movement

Erratics

-Large boulders that do not match local bedrock type or are found in

awkward elevations or places were likely transported there by a glacier

Eskers

-Long, winding hills of sediment deposited by streams beneath a

glacier

-Sediment will be sorted and rounded

Kames

-Rocky debris that is deposited in crevasses within a glacier to form a hill

Kettle Lakes

-When large chunks of the glacier break off and are partially buried,

they melt to form a kettle lake

Moraines

-Moraines are long hills that are composed of

material that a glacier has pushed or pulled along

-Rocks in moraines are unsorted and angular

Outwash Plain

-An outwash plain is where many streams (or just a few) flow out of the glacier as it melts

-The plain is relatively flat with sorted and

rounded sediments due to abrasion in the streams

Cirques, Aretes, Horns

-All features found in mountainous areas once covered by glaciers

Horn: Sharp point at mountain peak

Cirque: Bowl-shaped depression caused by abrasion

-Arete: Sharp ridge carved out of the mountainside

Wind Erosion and Weathering

-Abrasion is the dominant form of weathering in dry climates

-Rocks become “sand-blasted” and the

particles are blown away

Wind Deposition

-Sand and other particles are deposited in dunes

Wave Erosion and Weathering

-Abrasion is the dominant form of weathering

-Particles are washed on shore, swept back out, and gradually move in the direction of the

current

Long Shore Current

-Long shore currents flow parallel to the beach

-This steadily drags sediments along the shore in what is called long shore drift

Mass Movement

-The final, though less substantial type of

erosion is called mass movement

-Mass movement is the sliding of any rock

material or soil downhill as a result of gravity

-Some mass movement is slow, and some is

sudden

Landslide

-Landslide is a commonly used for the movement of a mass of bedrock or loose soil and rock down the slope of a hill, mountain or cliff

http://www.youtube.com/watch?v=23NZTzpw6cY

Creep

-Slow, imperceptible movement of soil down a slope

Slump

-Blocks of land that have tilted and moved

downhill along a surface that curves into the slope

Mudslides/Flows

-Rapid movement of Earth saturated with water