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Erosion – the process by which weathered
rock and soil particles are moved from
one place to another. There are 5 types
of erosion
Deposition – the process by which
sediments are laid down in new locations.
What is an
Erosion/Depositional System?
It is the combination of erosional
processes and the process of
deposition.
On a worldly scale erosion will equal
deposition. This is known as Dynamic
Equilibrium.
The transfer of rock and soil
down slope due to gravity
What causes Mass Movement?
1. Water – Heavy rains or melting snow over saturates the
surrounding surface materials with water
2. Oversteepend Slope: When the steepness of the land
exceeds a stable angle, it becomes more likely that
material will move down slope.
3. Earthquakes: Earthquakes shake large areas of land
which dislodges large amounts of rock, which are then
free to move down hill
4. Removal of vegetation: Plants keep slopes stable
because their roots hold together the soil.
• Landslide : weakening of
rocks/soil/vegetation due to
heavy rain.
• Mudflow: Weakening of just soil
• Rock Slide: weakening of rocks
• Avalanche: weakening of snow
• ** All of these have the power to
move millions of tons of material
very quickly
• Slump – another rapid type. Occurs when a
block of rock or soil on the face of a slope
slips down so that its upper surface is tilted
backwards (rotates).
• Earth flow – slow, caused by heavy rains, where a mass
of soil and plant life slowly slides down a slope.
• Soil Creep: slowest, caused by alternating periods of
freezing and thawing, animal activity, or water
movement. Particles move slowly downhill.
• Wind – the most active agent of erosion in deserts,
plowed fields and beaches.
• Types of wind erosion
•Deflation – fine particles are carried high up into
the air.
•Abrasion – larger particles roll or bounce along
the ground.
Wind erosion occurs more in deserts
because the sediments are dry and lighter
than in humid regions where sediments are
wet and heavier.
**Wind can only pick up
small light particles**
The amount of wind erosion is
dependent on:
1.
2.
3.
4.
•
size of the particles
speed of the wind
length of time the wind blows
resistance of the rocks.
An oasis forms when the wind erodes the desert until it
reaches the depth where water is present allowing
grass and trees to grow.
• Sand dunes – a mound of sand deposited by wind.
• They protect the area on the side of the dune away
from the ocean from further erosion, small plants
often grow here. Can vary in size and shape
• The side facing the wind has a gentle slope
(windward side), The top (crest), The other side (slip
face) is very steep.
Crest
Slip Face
Windward Side
• Loess are very fine particles of sand and silt
that is deposited far away from where it
originated.. deflation. Loess deposits are
very fertile
• Running water – the #1 cause of erosion.
• Rain can:
•Evaporate
•Sink into the ground
•Flow over the land as runoff
1. Amount of rainfall
2. Amount of plant
growth in an area
3. The shape of the
land: steep slopes =
more runoff because
it moves too fast to
soak into the ground.
1. Runoff: clay, sand, and gravel are pulled down
by gravity& it runs off the land
2. Rills: Water and sediment cut into soil forming
tiny grooves
3. Gullies: rills grow wider and deeper & form
tiny stream valleys. These act as channels for
future runoff.
4. Stream then river: When several
gullies come together, a large stream
forms.
• Drainage System: all the rills, gullies,
streams and rivers in an area
• Tributaries: Large streams that flow into
the main river.
• Drainage Basin: The area drained by a
main river and its channels… a HUGE
area
•Streams generally erode their channels by
lifting loose particles
•The stronger the current, the more erosional
power it has.
• Materials, like sand
and pebbles, are
carried in a stream
and can erode solid
rock by the process
of abrasion.
Streams transport material in three ways:
• In Solution: dissolved minerals, invisible
• In Suspension : carried by a fluid at the same speed
(largest part of streams load)
• bed load : scooting or rolling along the bottom: (too
large for suspension)
the maximum
load a stream
can carry.
• Immature river is V-shaped, steep
shorelines, waters flow very quickly,
waterfalls & rapids
• Wide U-shape river bottom, gentle slope of
shoreline, slow, no rapids/waterfalls, contains
meanders, natural levees & wide floodplains
Sediment settles out and causes a
process called sorting.
** Erosion occurs on the outside of meanders
** Deposition occurs on the inside of meanders
1. Oxbow lakes: cut off meander
2. Alluvial fans: sediments from a river are
dropped on the land forming a fan shape 3.
Deltas: sediments from a river are dropped into
water (Mississippi Delta)
• Glacier – a large mass of moving ice and snow. Forms
where there are many large snowfalls and the temp
remains very cold.
• Two kinds of glaciers, valley (alpine) and continental,
named for location
• Glacial ice erodes by abrasion and by plucking away at
the rock beneath it. One of the most powerful agents of
erosion.
• May carry large boulders as well as smaller particles of
rock.
• Till – rocks and soil deposited directly by a
glacier. Particles vary in size from large
boulders to fine clay. Not sorted at all.
• Moraines – formed when a glacier melts
and retreats leaving a ridge of till.
• Lateral moraine – till deposited along the
sides of a glacier.
• Terminal moraine – till deposited at the
front end of a glacier.
• Drumlins – an ovalshaped mound of till. Its
tip points in the direction
the glacier was moving.
• Melt water – streams
formed by melting ice.
• Outwash plains –
sediments deposited by
rivers of melt water; fanshaped; usually in front
of terminal moraines,
fertile land.
• Iceberg deposits – when parts of the glaciers break off and drift
into the sea.
• Glacial lakes – when the holes left by glaciers fill with water.
Examples: The Great Lakes, The Finger Lakes in New York.
• Kettle lakes –block of glacial ice is left behind and melts to form a
deep round hole that fills with the water from melting.
Striations left in rock from
glacier sliding over
• The powerful force of
waves constantly erodes
and shapes the shoreline.
• Under normal conditions,
waves erode about 1 to 1.5 meters per year. During storms it is
increased and can erode up to 25 meters per day.
The beach will erode during the winter and
build up in the summer.
•
•
•
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Sea cliffs- a steep vertical face of rock .
Terrace – when a sea cliff erodes it’s the flat platform left behind.
Sea stack – a column of resistant rock standing.
Sea cave –wave action erodes rock @ base of cliff
Sand bar: forms in the water
Spit: deposit that connects
two land masses
The shape of the shoreline results from changes in sea level.
Drop: cliffs and terraces
Rise: bays and harbors