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Agents of
Erosion &
Deposition
Chapter 11
Page 274 – 301
Page 276
Shoreline Erosion & Deposition
 Shoreline
= where land & a body of water meet.
 Erosion
= the breakdown & movement of
materials
 Deposition
= takes place when these materials are
dropped.
 Waves
can be powerful agents of erosion &
deposition.
Page 276
Wave Energy
 The
wind moves over the oceans surface,
producing ripples called waves. The size of a
wave depends on how hard the wind is blowing &
the length of time the wind blows.
 The
wind that comes from severe winter storms &
summer hurricanes generally produces the large
waves that cause shoreline erosion. Waves may
travel hundreds or even thousands of kilometers
form a storm before reaching the shoreline.
Page 277
Wave Trains
 Waves
don’t move alone. They travel in groups
called wave trains. As wave trains move away
from their source, they travel through the ocean
water without interruption. When they reach
shallow water, they change form & begin to break.
The ocean floor crowds the lower part of the
wave, shortening the wave length & increasing the
wave height. This results in taller, more closely
spaced waves. When the top of the wave becomes
so tall that in cannot support itself, it begins to
curl & break. These breaking waves are known as
surf.
Page 277
The Pounding Surf
 One
reason waves are so effective at picking up,
transporting, & depositing material is that they are
continually breaking.
 Another reason is that a tremendous amount of energy is
released when waves break. A crashing wave can break
solid rock or throw broken rocks back against the shore.
 The rushing water in breaking waves can easily wash
into cracks in rock, helping to break off large boulders
or fine grains of sand. The loose sand picked up by the
waves polishes & wears down coastal rocks. Waves can
also move sand & small rocks & deposit them in other
locations, forming beaches.
Page 278
Wave Deposits
 Waves
carry an assortment of materials, including
sand, rock fragments, & shells. Often this material
is deposited on the shore.
Beaches
 Beach
= any area of the shoreline made up of
material deposited by the waves.
 Not
all beaches are the same. The colors &
textures vary. This is because the type of material
found on a beach depends on its source.
Page 278
Wave Angle Makes a Difference
 The
movement of sand along a beach depends on
the angle at which the waves strike the shore.
 Most waves approach the beach at a slight angle
& retreat in a direction more perpendicular to the
shore. This move the sand in a zigzag pattern
along the beach.
Page 279
Offshore Deposits
 Waves
moving at an angle to the shoreline push water
along the shore, creating longshore currents.
 Longshore current = a movement of water parallel to &
near the shoreline. Sometimes waves erode material from
the shoreline, & a longshore current transports &
deposits it offshore, creating landforms in open water.
Some of these landforms are:
• Sandbar = an underwater or exposed ridge of sand,
gravel, or shell material
• Barrier spit = occurs when an exposed sandbar is
connected to the shoreline.
• Tombolo = an offshore island connected to the shore
by deposited material.
Page 279
Wave Erosion
 Wave
erosion produces a variety of features along
a shoreline. Sea cliffs are formed when waves
erode & undercut rock, producing steep slopes.
Waves strike the base of the cliff, wearing away
the soil & rock & making the cliff steeper. The
rate at which the sea cliffs erode depends on the
hardness of the rock & the energy delivered by the
wave. Sea cliffs made of hard rock, such as
granite, erode very slowly. Other sea cliffs, such
as those made of soft sedimentary rock, erode
rapidly, especially during storms.
Page 280
Coastal Landforms Created by Wave Erosion
Headland
 A finger-shaped
projection that occurs when
cliffs of hard rock erode more slowly than
surrounding rock. On many shorelines, hard
rock will form headlands, & the softer rock
will form beaches or bays. Thus, the coastline
will alternate between small, pocket-shaped
beaches & rocky headlands. This type of
shoreline is very common on the west coast of
the US
Page 280
Coastal Landforms Created by Wave Erosion
Sea stacks
 Offshore
columns of resistant rock that once
were connected to a sea cliff or headland. In
these instances, waves have eroded the sea
cliffs & headland, leaving behind isolated
columns of rock.
Page 280
Coastal Landforms Created by Wave Erosion
Sea caves
 Form
when waves cut large holes into fractured
or weak rock along the base of sea cliffs. Sea
caves are common in limestone cliffs, where
the rock is usually quite soft.
Page 280
Coastal Landforms Created by Wave Erosion
Sea arches
 Form
when wave action continues to erode a
sea cave, cutting completely through the
headland
Page 280
Coastal Landforms Created by Wave Erosion
Wave-cut terrace
 Forms
when a sea cliff is warn back ,
producing a nearly level platform beneath the
water at the base of the cliff. Here waves break
down the materials eroded from the sea cliffs.
As the waves cause the cliffs to retreat, rocks
eroded from the base of the cliff scrape the
wave-cut terraces until it is almost flat.
Page 282
Wind Erosion & Deposition
 Certain
locations are more vulnerable to wind
erosion than others.
 Areas
with fine, loose rock material which also
have little protective plant cover can be
significantly affected by the wind.
•
Plant roots anchor sand & soil in place,
reducing the amount of wind erosion.
 The
landscapes most commonly shaped by wind
processes are deserts & coastlines.
Page 282
Process of Wind Erosion
 Wind
moves material in different ways.
 Saltation = the movement of sand-sized particles by
a skipping & bouncing action in the direction the
wind is blowing. (happens in area where strong
winds occur)
 Deflation = the lifting & removal of fine sediment
by wind.
 Abrasion = the grinding & wearing down of rock
surfaces by other rock or sand particles. Abrasion
commonly occurs in areas where there are strong
winds, loose sand, & soft rocks.
Page 282
Wind-Deposited Materials
 All
material carried by the wind is eventually
deposited downwind.
 The faster the wind blows, the more material &
heavier the particles it can carry. As wind speed slows,
heavier particles are deposited first.
Dunes
 Dunes = a mound of wind-deposited sand.
Loess
 Loess = thick deposits of windblown, fine-grained
sediments. Found much further from their source
material
Page 287
Erosion & Deposition by Ice
 Glacier
 Because
= an enormous mass of moving ice.
glaciers are very heavy & have the
ability to move across the Earth’s surface, they are
capable of eroding, moving, & depositing large
amounts of rock materials.
Page 287
Glacier – Rivers of Ice
 Glaciers
form in areas so cold that snow stays on the
ground year-round.
• Areas like these are found at high elevations & in
polar regions.
• Because the average temperature is freezing or near
freezing, snow piles up year after year. Eventually,
the weight of the snow on top causes the deeppacked snow to become ice crystals, forming a
giant ice mass.
• These ice packs then become slow-moving “rivers
of ice” as they are set in motion by the pull of
gravity on their extraordinary mass.
Page 287
Types of Glaciers
 There
•
are two main types of glaciers:
Alpine – this type of glacier forms in
mountainous areas.

Valley glacier – form in valleys originally
created by stream erosion. These glaciers
flow slowly downhill, widening &
straightening the valleys into broad Ushapes as they travel downward.

Piedmont glacier – form at the base of
mountain ranges.
Page 288
Types of Glaciers (Cont’d)
•
Continental – not a true “river of ice” these
glaciers are the size of a continent.

Continental ice sheet – the largest type of
glacier.

Icebergs = large pieces of ice that break off
an ice shelf & drift into the ocean.

Calving – The process by which icebergs
forms
Page 289
Movement of Glaciers
 When
enough ice builds up on a slope, the ice
begins to move downhill.
 The
thickness of the ice & the steepness of the
slope determine how fast a glacier will move.
 Thick
glaciers mover faster than thin, & the
steeper the slop is, the faster glacier will move.
Page 289
Movement of Glaciers (Cont’d)
 Glaciers
move by two different methods.
• Glaciers move when the weight of the ice
causes the ice at the bottom to melt. The water
from the melted ice allows the glacier to move
forward, like a partially melted ice cube moving
across your kitchen counter.
• Glaciers also move when solid ice crystals
within the glacier slip over each other, causing a
slow forward motion. How
 Crevasse = a large crack that forms where the
glacier picks up speed or flows over a high point.
Page 290
Landforms Carved by Glaciers
 Alpine
& continental glaciers produce landscapes
that are very different from one another.
 Alpine
glaciers carve out rugged features in the
mountain rocks through which they flow.
 Continental
glaciers smooth the landscape by
scraping & removing features that existed before
the ice appeared, flattening even some of the
highest mountains.
Page 290
Landforms Carved by Glaciers
 striations
Page 290
Landforms Carved by Glaciers
Cirques
 Are
bowl-like depressions where glacial ice
cuts back into the mountain walls.
Page 290
Landforms Carved by Glaciers
Arêtes
 Are
jagged ridges that form between two or
more cirques cutting into the same mountain
Page 290
Landforms Carved by Glaciers
U-shaped valleys
 Are
formed when a glacier flows into & erodes
a valley, changing the valley form its original
v-shape to a u-shape. These broad u-shaped
glacial valleys are called glacial troughs.
Page 290
Landforms Carved by Glaciers
Horns
 Are
sharp, pyramid-shaped peaks that form
when three or more cirques erode the mountain
Page 290
Landforms Carved by Glaciers
Hanging valleys
 Are
smaller glacier valleys that join the deeper
main valley. These valleys form because
smaller glaciers cannot carve a valley as deep
as the main glacier. Many hanging valleys form
waterfalls after the ice is gone.
Page 292
Types of Glacial Deposits
 Glacial
drift = general term used to describe all
material carried & deposited by glaciers.
 Glacier
drift is divided into two main types, based
on whether the material is sorted or unsorted.
Page 292
Stratified Drift
 Stratified
drift = rock material that has been
sorted & deposited in layers by water flowing
from the melted ice.
 Many streams are created by the melt-water for
the glacier. These streams carry an abundance of
sorted material, which is deposited in front of the
glacier in a broad area called an outwash plain.
Page 292
Stratified Drift (Cont’d)
 Sometimes
a block of ice is left in the outwash
plain when the glacier retreats. During the time it
takes for the ice to melt, sediment builds up
around the block of ice. After the ice has melted, a
depression called a kettle is left.
 Kettle commonly fill with water, forming a lake or
pond.
Page 292
Stratified Drift
 Some
melt-water streams flow in tunnels along
the bottom of the melting glacier. The melt-water
moves through crevasses & cracks in the ice,
creating tunnels that run downhill. Through these
tunnels, the streams transport sand & gravel,
which are later deposited in long, narrow, winding
ridges called eskers. When the glacier melts back,
the esker is revealed.
Page 293
Till Deposits
 The
second type of glacier drift, till, is unsorted
rock material that is deposited directly by the ice
when it melts.
 Unsorted means that the till is made up of
different sizes of rock material, ranging from large
boulders to fine glacial silt. As a glacier flows, it
carriers different sizes of rock fragments. When
the glacier melts, the unsorted material is
deposited on the ground surface. The most
common till deposits are moraines.
Page 294
Gravity’s Effect on Erosion & Deposition
 Waves,
wind, & ice are all agents of erosion &
deposition that you can see. And though you can’t
see it & might not be aware of it, gravity is also an
agent of erosion & deposition constantly at work on
the Earth’s surface. Gravity not only influences the
movement of water, such as waves, streams, & ice,
but also causes rocks & soil to move downslope.
 Mass
movement = the movement of any material,
such as rock, soil, or snow, downslope. Mass
movement is controlled by the force of gravity &
can occur rapidly or slowly.
Page 294
The Forces in Mass Movement
 All
mass movement occurs on slopes as a result of
gravitational pull.
 The
effect of gravity on the surface material
depends on many of the surface material’s
characteristics, such as its size, weight, shape, &
moisture level.
 Another
factor that influences mass movement is
the slope on which the surface material rests. The
steeper the slope is, the more likely it is that mass
movement will occur.
Pages 295 – 296
Rapid Mass Movement
is the most destructive type of mass movement –
it can occur suddenly & without warning – it often
destroys everything in it’s path
 Rock fall = happens when a group of loose rocks falls
down a steep slope
 Landslide = the sudden & rapid movement of large
amounts of material downslope.
 Slump = occurs when a block of material moves
downslope.
 Mudflow = a rapid movement of a large mass of mud.
The most dangerous in this category is a lahar
 This
Pages 296 – 297
Slow Mass Movement
 Sometimes
you don’t even notice mass movement
occurring. The most frequent mass movement is
creep.
 Creep = extremely slow movement of material
downslope.
 Solifluction = occurs in the artic & alpine climates
where only the top layer of soil thaws.