Transcript Agents of Erosion and Deposition

Agents of Erosion and
Deposition
Shoreline Erosion and
Deposition
Shoreline Erosion and
Deposition
The results of
erosion can
often be
dramatic. For
example, this
sinkhole
formed in a
parking lot in
Atlanta,
Georgia,
when water
running
underground
eventually
caused the
surface of the
land to
collapse.
Section 1
Wave Energy
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When waves crash
into rocks over long
periods of time, the
rocks are broken
down into smaller and
smaller pieces until
they become sand.
Waves usually play a
major role in building
up and breaking down
the shoreline. A
shoreline is the
boundary between
land and a body of
water.
Wave Energy, continued
2
 As the wind moves
across the ocean surface,
it produces ripples called
waves. The size of a
wave depends on how
hard the wind is blowing,
the distance over which it
blows (fetch) and how
long the wind blows.
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The wind that results
from summer hurricanes
and severe winter storms
produces large waves
that cause dramatic
shoreline erosion.
This photo, taken while the Virginia
Beach Erosion Control and Hurricane
Protection Project was underway,
shows the significant difference
between the unimproved area (top of
photo) and the area of the widened
beach berm already completed.
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Wave Energy, continued
3
Wave Trains Waves
travel in groups called
wave trains. When wave
trains reach shallow water,
the bottom of the wave
drags against the sea floor,
slowing the wave down.
The upper part of the
wave moves more rapidly
and grows taller, and
begins to curl and break.
These breaking waves are
known as surf.
The time interval between
breaking waves is called
the wave period.
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Wave Energy, continued
The Pounding Surf
4
Tremendous energy is
released when waves break.
Crashing waves can break
solid rock and throw broken
rocks back against the
shore.
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Breaking waves also wash
away fine grains of sand,
which are picked up by the
waves and wear down and
polish coastal rock.
The process continues until
rock is broken down in
smaller and smaller pieces
that eventually become
sand.
Breaking waves
crash against the
rocky shore,
releasing their
energy.
Wave Erosion
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Shaping a Shoreline Wave
erosion produces a variety of
features along a shoreline.
Much of the erosion
responsible for coastal
landforms takes place during
storms.
Sea cliffs are formed when
waves erode and undercut
rock to produce steep slopes.
The next two slides show
some of the major features
that result from wave erosion.
Wave Deposits
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Beaches are areas of the
shoreline made up of
material deposited by
waves. Some beach
material is also deposited
by rivers.
Waves carry a variety of
materials, including sand,
rock fragments, dead
coral, and shells.
The colors and textures of
beaches vary because the
type of material found on a
beach depends on its
source.
Wave Deposits, continued
2
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Wave Angle and Sand Movement Waves
moving at an angle to the shoreline push water
along the shore and create longshore currents.
Longshore currents move sand in a zigzag
pattern along the beach.
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Wave Deposits, continued
3
Offshore Deposits When
waves erode material from
the shoreline, longshore
currents can transport and
deposit the material offshore,
which creates landforms in
open water.
A sandbar is an underwater
or exposed ridge of sand,
gravel, or shell material.
A barrier spit is an exposed
sandbar connected to the
shoreline.
A barrier spit, such as Cape
Cod, Massachusetts, occurs
when an exposed sandbar
is connected to the
shoreline.
Wind Erosion and
Deposition
The Process of Wind Erosion
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Saltation is the skipping and bouncing movement of sand
or other sediments, caused by wind or water.
Moving sand grains knock into one another, bounce up into
the air, fall forward, and strike other sand grains, causing
them to roll and bounce forward.
The Process of Wind Erosion,
continued 2
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Deflation is a form of
wind erosion in which fine,
dry soil particles are blown
away, removing the top
layer of fine sediment or
soil and leaving behind
rock fragments that are
too heavy to be lifted by
the wind.
Deflation may cause
desert pavement, which
is a surface consisting of
pebbles and small broken
rock.
Scooped-out depressions
in the landscape are called
deflation hollows.
Desert pavement, such as that
found in the Painted Desert in
Arizona, forms when wind
removes all the fine materials.
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The Process of Wind Erosion,
continued
3
Abrasion is the grinding
and wearing away of rock
surfaces through the
mechanical action of other
rock or sand particles.
Abrasion commonly
happens in areas where
there are strong winds,
loose sand, and soft rocks.
The blowing of millions of
sharp sand grains creates
a sandblasting effect,
helping erode, smooth,
and polish rocks.
Picture shows the powerful
effect of wind generated
abrasion is the Double Arch
from Arches National Park.
Wind-Deposited Materials
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Loess is a deposit of
windblown, finegrained sediment.
Because wind can
carry fine-grained
material much higher
and farther than it
carries sand, loess
deposits are
sometimes found far
from their source.
Wind-Deposited Materials,
continued 2
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Dunes When the wind
hits an obstacle, the wind
slows down, depositing the
heavier material. The
material collects, creating
an additional obstacle and
eventually forming a
mound that buries the
original obstacle.
The mounds of winddeposited sand are called
dunes. A dune keep its
shape, even though it
moves.
Wind-Deposited Materials,
continued 3
• The Movement of Dunes Different wind
conditions produce dunes in various
shapes and sizes. A dune usually has a
gently sloped side and a steeply sloped
side, called a slip face.
Erosion and Deposition
by Ice
Glaciers—Rivers of Ice
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A glacier is a large mass
of moving ice. They are
capable of eroding,
moving, and depositing
large amounts of rock
materials.
Glaciers form in areas so
cold that snow stays on
the ground year-round.
Because glaciers are so
massive, the pull of gravity
causes them to flow
slowly, like “rivers of ice.”
Glaciers—Rivers of Ice, continued 2
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Alpine Glaciers form
in mountainous areas.
One common type of
alpine glacier is a
valley glacier.
Valley glaciers form
in valleys originally
created by stream
erosion. As these
glaciers slowly flow
downhill, they widen
and straighten the
valleys into broad U
shapes.
Valley Glacier: a
valley flowing
glacier. These
glaciers may be
the combination
of several smaller
glaciers joining
and flowing
together down a
large valley.
Glaciers—Rivers of Ice, continued 3
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Continental Glaciers are
huge, continuous masses
of ice that can spread
across entire continents.
The largest continental
glacier in the world covers
almost all of Antarctica.
This ice sheet is
approximately one and a
half times the size of the
United States, and is more
than 4,000 m thick in
some places.
Glaciers—Rivers of Ice, continued 4
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Glaciers on the Move
When enough ice builds up
on a slope, the ice begins
to move downhill. Thick
glaciers move faster than
thin glaciers, and the
steeper the slope, the
faster the glaciers will
move.
Glaciers move in two
ways: sliding and flowing.
A glacier slides when its
weight causes the ice at
the bottom to melt. A
glacier flows as ice crystals
within the glacier slip over
each other.
Glaciers—Rivers of Ice, continued 5
• Glacier movement is affected by climate.
As the Earth cools, glaciers grow. About
10,000 years ago, a continental glacier
covered most of North America.
Landforms Carved by Glaciers
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Continental glaciers and
alpine glaciers produce
landscapes that are very
different from one
another.
Continental glaciers
smooth the landscape
by scraping and eroding
features that existed
before the ice
appeared.
Alpine glaciers carve
out large amounts of
rock material and create
spectacular landforms.
Landforms Carved by Glaciers 2
Glacial Landscape Features
Types of Glacial Deposits
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As a glacier melts, it drops all the material it is
carrying. Glacial drift is the general term used
to describe all material carried and deposited by
glaciers.
Glacial drift is divided into two main types, till
and stratified drift.
Types of Glacial Deposits,
continued 2
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Till Deposits Unsorted
rock material that is
deposited directly by
the ice when it melts is
called till. Unsorted
means that the till is
made up of rock
material of different
sizes.
The most common till
deposits are moraines.
Moraines generally form
ridges along the edges
of glaciers.
Moraines
Types of Glacial Deposits,
continued
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Stratified drift is a glacial
deposit that has been sorted
and layered by the action of
streams or meltwater.
Streams carry sorted material
and deposit it in front of the
glacier in a broad area called
an outwash plain.
Sometimes, a block of ice is
left in an outwash plain when
a glacier retreats. As the ice
melts, sediment builds up
around the block of ice,
forming a depression called a
kettle.
The Effect of Gravity on
erosion and Deposition
Angle of Repose
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Gravity is an agent of
erosion and
deposition. It
influences the
movement of water
and ice, and it causes
rocks and soil to move
downslope.
Mass movement is
the movement of any
material, such as rock,
soil, or snow,
downslope.
Angle of Repose, continued 2
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Material such as rock, soil,
or snow moves downhill
until the slope becomes
stable. The angle of repose
is the steepest angle at
which loose material will
not slide downslope.
The angle of repose is
different for different
surface material. Size,
weight, shape, and
moisture level determine
at what angle material will
move down-slope.
If the slope on which material
rests is less than the angle of
repose, the material will stay
in place. If the slope is
greater than the angle of
repose, the material will
move downslope.
Rapid Mass Movement
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Rock falls happen
when loose rocks fall
down a steep slope.
The rocks can range in
size from small
fragments to large
boulders.
Mass movements,
like rock falls, happen
suddenly and rapidly,
and can be very
dangerous.
Rapid Mass Movement, continued 2
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Landslides are
sudden and rapid
movements of a large
amount of material
downslope.
.
Slumps
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The most common
type of landslide is
a slump. Slumping
occurs when a
block of land
becomes detached
and slides downhill
Rapid Mass Movement, continued 3
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Mudflows are rapid
movements of large
masses of mud.
Mudflows happen when
a large amount of water
mixes with soil and
rock. The water causes
the slippery mass of
mud to flow rapidly
downslope.
Mudflows commonly
happen in mountainous
regions when a long dry
season is followed by
heavy rains.
Mudflow-damaged house
along the Toutle River.
The height of the
mudflow is shown by the
"bathtub-ring" mudlines
seen on the tree trunks
and the house itself.
Caused by eruption of Mt.
St. Helens May 18, 1980.
Rapid Mass Movement, continued 4
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Lahars are mudflows
caused by volcanic
eruptions or heavy rains on
volcanic ash. Lahars can
travel at speeds grater than
80 km/h and can be as
thick as cement.
On volcanoes with snowy
peaks, an eruption can
suddenly melt a great
amount of ice. Water from
the ice liquefies the soil and
volcanic ash to produce a
hot mudflow that rushes
downslope.
A lahar overtook
this area on the
island of Kyushu
in Japan.
Slow Mass Movement
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Creep is the slow
mass movement of
material downslope.
Although rapid mass
movements are visible
and dramatic, slow
mass movements
happen a little at a
time. However, slow
mass movements
occur more frequently,
and more material is
moved collectively.