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Agents of Erosion and Deposition


Title: Agents of Erosion and Deposition Author: Cobb County School District Last modified by: David Brown Created Date: 9/26/2008 12:08:37 AM Document presentation format – PowerPoint PPT presentation

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Title: Agents of Erosion and Deposition

Agents of Erosion and Deposition
  • Chapter 12

Shoreline Erosion and Deposition
  • Chapter 12
  • Section 1

Water The Major Agent of Erosion
  • What Is Erosion? Erosion is the process by which
    soil and sediment are transported from one
    location to another.
  • Water and Erosion Water is a major agent of
    erosion. Rivers often carry eroded materials long

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
  • Section 1

Wave Energy
  • 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.
  • 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
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.

Section 1 Shoreline Erosion and Deposition
Chapter 12
Wave Period of Ocean Waves
Click below to watch the Visual Concept.
Visual Concept
Wave Energy, continued4
  • The Pounding Surf Tremendous energy is released
    when waves break. Crashing waves can break solid
    rock and throw broken rocks back against the
  • 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
  • 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.

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Wave Deposits
  • 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, continued2
  • 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.

Wave Deposits, continued3
  • 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
  • Chapter 12
  • Section 2

Wind Erosion
  • Normally the weakest, slowest type of erosion.
  • Over 1000s of years however, winds can move vast
    quantities of sediment, and grind down even the
    strongest rock.

The Process of Wind Erosion
  • Saltation is the skipping and bouncing movement
    of sand or other sediments, caused by wind or
  • 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
  • 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
  • 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.
The Process of Wind Erosion, continued3
  • 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
  • Loess is a deposit of windblown, fine-grained
    sediment. Usually formed during glacial periods.
  • Because wind can carry fine-grained material
    much higher and farther than it carries sand,
    loess deposits are sometimes found far from their
  • Very rich and fertile.

Section 2 Wind Erosion and Deposition
Chapter 12
Click below to watch the Visual Concept.
Visual Concept
Wind-Deposited Materials, continued 2
  • 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 wind-deposited sand are called
    dunes. A dune keeps its shape, even though it
  • Dunes move in the same direction the wind does.

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
  • Chapter 12
  • Section 3

GlaciersRivers of Ice
  • 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.

GlaciersRivers of Ice, continued 2
  • Alpine Glaciers form in mountainous areas. One
    common type of alpine glacier is a valley
  • 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.
GlaciersRivers of Ice, continued 3
  • 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.

GlaciersRivers of Ice, continued 4
  • 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.

Section 3 Erosion and Deposition by Ice
Chapter 12
Movement of Glaciers
Click below to watch the Visual Concept.
Visual Concept
GlaciersRivers 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

Landforms Carved by Glaciers
  • Continental glaciers and alpine glaciers produce
    landscapes that are very different from one
  • 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
  • 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
  • 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

Types of Glacial Deposits3
  • 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.

Section 3 Erosion and Deposition by Ice
Chapter 12
Glacial Drift Stratified Drift and Till
Click below to watch the Visual Concept.
Visual Concept
The Effect of Gravity on Erosion and Deposition
  • Chapter 12
  • Section 4

Angle of Repose
  • 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
  • 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
  • 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 2
  • Landslides are sudden and rapid movements of a
    large amount of material downslope.
  • .

  • The most common type of landslide is a slump.
    Slumping occurs when a block of land becomes
    detached and slides downhill

Rapid Mass Movement 3
  • 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

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 4
  • 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
  • Creep is the slow mass movement of material
  • 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

Section 4 The Effect of Gravity on Erosion and
Chapter 12
Click below to watch the Visual Concept.
Visual Concept
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