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
Increasing Size
-Rock Particles are categorized
into 6 types:
-Boulders
-Cobbles
-Pebbles
-Sand
-Silt
-Clay
*Dissolved minerals are
also transported
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 “sandblasted” 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