Transcript Wave Energy, continued

Bellringer
Where does sand come from? Many people find
the sound of waves on a beach very relaxing and
peaceful. However, each wave that comes ashore
carries a certain amount of destructive force.
Write a short poem about how ocean waves create
sand from rock.
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
• 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 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.
Wave Energy, continued
• 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.
Wave Energy, continued
• The Pounding Surf Tremendous energy is
released when waves break. Crashing waves can
break solid rock and throw broken rocks back against
the shore.
• 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.
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.
Sea Arch
Sea Cave
Wave-cut terrace
Headlands
Sea cliffs
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, continued
• 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, continued
• 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.
Bellringer
What causes wind? Why are some wind currents
stronger than others? Have you ever been near a
tornado or typhoon? A hurricane or straight-line
windstorm? What happened?
Write your answer in your science journal.
The Process of Wind Erosion
• 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
• 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.
The Process of Wind Erosion, continued
• 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.
Wind-Deposited Materials
• Loess is a deposit of windblown, fine-grained
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.
Chapter G3
Wind-Deposited Materials, continued
• 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 keep its shape, even though it
moves.
Wind-Deposited Materials, continued
• 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.
Bellringer
Fourteen thousand years ago, much of North
America was covered in a thick layer of ice called
a continental glacier, which moved as far south as
southern Illinois. Humans were living in North
America at the time.
Write a paragraph about being an early human
and discovering this glacier.
Glaciers—Rivers 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.”
Glaciers—Rivers of Ice, continued
• 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.
Glaciers—Rivers of Ice, continued
• 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
• 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.
Movement of Glaciers
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Glaciers—Rivers of Ice, continued
• 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
• 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.
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
• 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.
Types of Glacial Deposits, continued
• 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.
Glacial Drift: Stratified Drift and Till
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Bellringer
“Watch for falling rock!”
Where would a warning sign like this be
necessary? Have you ever seen one of these
signs on a highway or trail? What factors
contribute to making a rock-fall zone?
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
• 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 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, continued
• 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, continued
• 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.
Rapid Mass Movement, continued
• 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.
Slow Mass Movement
• 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.
Creep
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.