Wind & Waves
Wind & Waves TB Ch. 7 & 16 BFRB P.105 -116 & 122-126 Regents Earth Science Mrs. O’Gorman
Name: __________________
Wind & how it weathers, erodes & deposits sediments
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Name ____________________________________ Date __________ Class ___________________
SECTION 8-6
SECTION SUMMARY
Wind Guide for Reading ◆ How does wind
cause erosion? ◆ What features result from deposition by wind?
Unit 3 Resources
W
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Science Explorer Earth Science
© Prentice-Hall, Inc.
58
ind by itself is the weakest agent of erosion. Yet wind can be a powerful force in shaping the land in areas where there are few plants to hold the soil in place. For example, in deserts few plants grow, and wind can easily move the grains of dry, light sand. The main way that wind causes erosion is by deflation. Geologists define deflation as the process by which wind removes surface materials. When wind blows over the land, it picks up particles of sediment. The stronger the wind, the larger the particles that it can pick up and move through the air. Particles that are too heavy to be picked up might skip or bounce for a short distance. Strong winds can even roll heavier sediment particles over the ground. Deflation does not usually have a great effect on the land. In deserts, though, deflation can sometimes create an area of rock fragments called desert pavement. There, wind has blown away the smaller sediment. All that remains are rocky materials that are too large and heavy to be moved by wind. Abrasion by wind-carried sand can polish rock, but it causes little erosion. At one time, geologists thought such abrasion cut the stone shapes seen in deserts. But evidence now shows that most desert landforms are the result of weathering and water erosion. All sediment picked up by wind eventually falls to the ground. This happens when wind slows down or some obstacle, such as a boulder or clump of grass, traps the windblown sand and other sediment. Wind erosion and deposition may form sand dunes and loess deposits. A sand dune is a deposit of wind-blown sand. When wind carrying sand strikes an obstacle, the result is usually a sand dune. Sand dunes can be seen on beaches and in deserts where wind-blown sediment has built up. Sand dunes come in many shapes and sizes. Sand dunes often move over time. Plant roots can help anchor a sand dune in one place. Sand dunes are most often made of the coarser sediments carried by wind. The finer sediments are often deposited in layers far from their source. This fine, wind-deposited sediment is loess. Large loess deposits are found in central China and in such states as Nebraska, South Dakota, Iowa, Missouri, and Illinois. Loess helps form fertile soil.
The desert landscape has many interesting geologic features. How do the agents of WED create this landscape?
Weathering & Erosion By Wind • Dry Climates (soil made of dry & loose sand, silt, & clay which are easily carried by wind) • Mechanical weathering by ABRASION (wind carries sediments and blows them against rocks – like sandpaper) • Sediments eroded by wind have a frosted appearance
Weathering & Erosion By Wind
Note…no solution…WHY?
• VENTIFACTS – larger rocks in arid regions shaped by wind-blown sand hitting into and abrading them. They will have a pitted surface.
– Sometimes, the wind direction varies and the rocks get abraded on all sides. – Sometimes, the sides of the rocks facing the prevailing wind are worn smooth over time and have a distinct angled side.
SAND DUNES
VIF!!!!!
• Large piles of sand deposited by wind – Usually start piling up against rocks, bushes, clumps of grass, etc…
• Side of the dune facing the wind (WINDWARD SIDE) has a long gentle slope • Side opposite (LEEWARD SIDE) is a short, steep slope – also known as the “slip face” (like if you tried to walk down it you’d slip because it’s steep…)
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You need to be able to draw the dune if given the wind direction and the wind if given the dune shape!
DEFLATION VIF!!!!
• Wind removes the top layer of soil, clay and silt, causing the ground surface to lower over time and leaving behind courser sediments. – The soil “DEFLATES” (like a bicycle tire) and there can be small depressions or “blowouts” with larger rocks creating a “pavement”. That’s when the deflation process will end as those sediments are too large to be moved by the wind.
Erosion by Wind
Deflation “pits”
• If soil is not “held down” via plant roots and sufficient moisture content, the soil can be eroded away easily by wind. – The removal of soil makes the farmland unusable. – This can create very bad dust storms when the winds increase in velocity. – This created the dustbowl in the plains states during the 1930’s (Great Depression)
Desert pavement
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Erosion by Wind • Today, a common place people experience dust storms is in Phoenix and Tuscon, Arizona. • These storms are called Haboobs and occur during the dry summers in the southwest. • They can be very scary and dangerous – especially for drivers!
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Waves, longshore currents & Shoreline Erosional & Depositional Features Page 11 of 45
Name ____________________________________ Date __________ Class ___________________
SECTION 8-5
SECTION SUMMARY
Waves Guide for Reading ◆ What gives ocean
waves their energy? ◆ How do ocean waves shape a coast?
Unit 3 Resources
O
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Science Explorer Earth Science
© Prentice-Hall, Inc.
54
cean waves contain energy. The energy in waves comes from wind that blows across the water’s surface. As the wind makes contact with the water, some of its energy transfers to the water. The energy of a wave causes water particles to move up and down as the wave goes by. But the water particles themselves don’t move forward. Only the form of the wave moves. A wave changes as it approaches land. In the shallow water near the shore, the water actually does move forward with the wave. This forward-moving water provides the force that shapes the coast. Waves are a major force of erosion along coasts. One way waves erode is by impact. The energy in waves can break apart rocks and make cracks in rocks larger. Waves also erode by abrasion. As a wave approaches shallow water, it picks up sediment. When the wave hits land, the sediment wears away rock. Waves coming to shore gradually change direction as different parts of a wave begin to drag on the bottom. For instance, incoming waves bend as they approach a headland. A headland is a part of the shore that sticks out into the ocean. The waves concentrate their energy on the headland, and eventually wear it down, evening out the shore. When waves hit a steep, rocky coast, they strike the area again and again. Along a steep coast, waves will erode the base of the land, especially where the rock is softer. Over time the waves may erode a hollow area, called a sea cave. Eventually, waves may erode the base of the land so much that the rock above collapses. The result is a wave-cut cliff. Other landforms created by wave erosion include sea arches and sea stacks. Waves not only erode the land, they also deposit sediment. Waves shape the coast through both erosion and deposition. Deposition occurs when waves slow down and the water drops its sediment. As waves reach the shore, they drop the sediment they carry, creating a beach. A beach is an area of wave-washed sediment along a coast. Most beach sand comes from rivers that carry eroded particles of rock into the ocean. Some beaches are made of small fragments of coral or sea shells piled up by wave action. The sediment on a beach usually moves after it has been deposited. Waves usually hit a beach at an angle, creating a current that runs parallel to the coastline. As repeated waves hit the beach, some of the sediment moves down the beach with the current, in a process called longshore drift. One result of longhore drift is the formation of a spit, a beach that projects like a finger into the water. Incoming waves carrying sand may build up sandbars, long ridges of sand parallel to the shore. A barrier beach is similar to a sandbar, but a barrier beach forms when storm waves pile up sand above sea level. Barrier beaches are found in many places along the Atlantic coast of the United States.
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What Creates Waves? • Wind blowing the surface of the water causing it to “pile up” • HEIGHT depends on 3 things: 1 – wind speed 2 – wind duration - length of time the wind blows over the water 2 – distance the wind blows over the open water – “FETCH”
Why is the wave height so great in the Southern Ocean?
Wave Features • Waves cause surface water to rise & fall Top of the wave = CREST • Bottom of wave = TROUGH • WAVE HEIGHT is the difference between the crest and trough • WAVE LENGTH is the distance from one crest to the next crest (or trough to trough) • AMPLITUDE the distance from the baseline (sea level) to the top of the crest or bottom of the trough.
• Ocean waves transmit the energy that the wind transferred through them. The water molecules don’t move through the ocean, just the energy!
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Waves in Shallow Water • BREAKERS – waves that enter shallow water, slow down & “break” – The bottom of the wave “scrapes” along the bottom of ocean & slows down due to friction, this reduces its wavelength. – The reduction in wavelength (horizontal) increases the wave height (vertical) – (Conservation of energy.) – The crest (top) of the wave continues forward at the same speed & falls over onto the beach. (The crest is not moving faster, it just appears to move faster because the bottom part of the wave is moving slower!!!)
As waves enter shallower water (less than half of the wavelength), their wavelength decreases which causes their height to increase!
As waves enter shallower water (less than half of the wavelength), their wavelength decreases which causes their height to increase!
Waves in Shallow Water • Waves always approach the shoreline at an angle • As the wave enters water, the part of the wave that “hits” the shallow shoreline first, slows down (due to friction) and the part of the wave that isn’t hitting the shoreline keeps moving at the same speed. • The wave crest direction “bends” due to the difference in speed. • Shoreline waves REFRACT & hit the shore almost parallel to shore BUT NOT PARALLEL!!!!!
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CURRENTS • All of this wave physics and refraction leads us to what we really NEED to know… • Phenomena ---Ever notice how when you get out of the ocean after swimming you’re farther down the beach from where you went in?!?!
• VIF!!! LONGSHORE CURRENTS – move parallel to shoreline & carry sand down the beach (erosion) • Their direction is determined by examining the direction of the wave crests that are hitting the shore when looking from above.
Longshore Current: VIF!!!! transportation of sediments parallel to the beach…this is the current that can transport you parallel to the beach as well!
• SWASH – water moving ONTO the beach • BACKWASH – water moving back off beach – Pulls sand from the beach into the water – UNDERTOW – a strong backwash – very dangerous for Ocean small children!
Which direction is the longshore current moving in this photo?
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Human’s build Jetties, Groins and Breakwaters to prevent erosion and build up the width of beaches by forcing deposition. Which direction is the longshore current moving in this photo? Draw an arrow.
FYI & Safety! • RIP CURRENTS – very strong currents that move OUTWARD from the shore • The geology of the area under the water creates them. • The WORST thing to do if caught in a rip current is to panic & try to swim directly to shore! The current is too strong & you will fatigue and drown! Swim across the current (parallel to the shore) to escape the current!
FYI - Littoral current is another name for longshore current…
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SHORELINE FEATURES Very energetic waves easily erode soft rocks found along deep water shorelines Sea Cliffs, Sea Arches, Sea Caves, and Sea Stacks are commonly found off the coast of Maine, California, Oregon, Hawaii, Canada and Australia. Pick out the headlands, cliffs, arches, caves and stacks on the following slides!!!!
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Haystack Rock, OR
People!!!
Less energetic waves deposit a lot of sediments along the eastern shores of the USA! • Longshore currents deposit large amounts of sediment over time. • A SANDBAR is formed when ocean currents deposit sand near the shore. Sandbars may take many different forms… • 1) BARRIER ISLANDS are LARGE sandbars parallel to shore (Fire Island, NY & the Outer Banks, NC)
– Barrier islands protect the shoreline from the full strength of waves – These shoreline features are NOT permanent! They are constantly being built up and destroyed by waves! – Most of the Eastern Coast of the USA has Barrier Islands and flat sandy beaches.
Barrier Islands… think Fire Island, Long Island and Outer Banks, No. Carolina
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Spit: sandbar that is connected to land on one side of a bay
Bay: indentation of shoreline creating a body of water connected to an ocean
Baymouth Bar – a sandbar (overgrown spit) that completely closes access to a bay, thus closing it off from the main body of water creating a lagoon
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Think – San Francisco Bay…Hudson Bay…
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NAME:_______________________________________________
Date:_________________
Per #:_______
Investigating Coastal Processes GO TO SITE: https://ees.as.uky.edu/sites/default/files/elearning/module14swf.swf R EAD THE O PENING PARAGRAPH. C LICK O N THE O VERVIEW LINK B EACH A NATOMY:
T ASK # 1: L ABEL THE M AIN COMPONENTS O F A BEACH SYSTEM
C LICK O N THE RIGHT A RROW N EXT TO B EACH A NATOMY, IT SHOULD N OW SAY W AVE ANATOMY. P RESS THE START BUTTON TO SEE BREAKERS F ORM . P RESS I T S EVERAL T IME T O S EE T HE P ROCESS R EPEAT F OR A B ETTER U NDERSTANDING O F I T . T ASK # 2: D EFINE THE KEY TERMS O F THE A NATOMY O F A W AVE – U SE THE BLACK ARROWS AT THE FAR FIGHT SCROLL U P A ND D OWN TO R EAD T HE I NFORMATION Crest: Trough: Wave Height: Page 26 of 45
Wavelength: Amplitude: Breaker: T ASK#3: C LICK THE RIGHT A RROW AFTER W AVE ANATOMY. IT SHOULD N OW SAY W AVE M OTION . R EAD THE PARAGRAPH AND F OLLOW T HE D IRECTIONS . Waves break because the top of the wave orbitals keep moving at the ______________________________________, while the bottom of the wave oribitals __________________________ due to the friction from the ocean floor. T ASK # 4: CLICK O N THE RIGHT ARROW A FTER W AVE M OTION . IT SHOULD NOW SAY W AVE REFRACTION . R EAD THE PARAGRAPH A ND A NSWER T HE F OLLOWING Q UESTIONS . Why do waves refract inward towards the beach?_________________________________________________________ __________________________________________________________________________________________________ What are the names of the 2 structures that humans build that make the water more shallow and slows down the waves? ______________________ and _________________________ T ASK#5: CLICK O N THE RIGHT ARROW AFTER W AVE REFRACTION . IT SHOULD SAY LONGSHORE CURRENT. W ATCH THE ANIMATION A ND R EAD T HE P ARAGRAPH . A NSWER T HE F OLLOWING Q UESTION .
Define Longshore current: __________________________________________________________________________ _________________________________________________________________________________________________ Does the longshore current run in the same direction or opposite direction as the incoming wave crests? ______________________________________________________________ Task #6: CLICK O N THE RIGHT ARROW A FTER LONGSHORE CURRENT. IT SHOULD SAY RIP CURRENTS. W ATCH THE ANIMATION A ND R EAD T HE P ARAGRAPH . A NSWER T HE F OLLOWING Q UESTION .
What would you do to escape a rip current?_____________________________________________________________
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T ASK # 7: CLICK O N THE RIGHT ARROW A FTER RIP CURRENTS. IT SHOULD SAY COASTAL D EPOSITIONS. W ATCH THE A NIMATION AND READ T HE P ARAGRAPH . L ABEL THE FOLLOWING O N THE D IAGRAM : W AVE CREST, LONGSHORE CURRENT, AREA O F D EPOSITION (SEVERAL), AREA O F EROSION (SEVERAL). T ASK # 8: C LICK O N THE RIGHT A RROW A FTER C OASTAL D EPOSITION. R EAD A BOUT H OW A SEA STACK COULD BE FORMED FROM A H EADLAND . T ASK # 9: CLICK O N THE RIGHT ARROW A FTER COASTAL DEPOSITIONS. IT SHOULD SAY COASTAL EROSIONS LANDFORMS. WATCH T HE A NIMATION A ND R EAD T HE P ARAGRAPH . C LICK O N T HE R IGHT A RROW A GAIN . I T S HOULD S AY C OASTAL E ROSION : CONTROLS . C LICK O N E ACH O F T HE C ONTROLS T O S EE H OW T HEY A FFECT D EPOSITION .
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T ASK # 10: FINALLY, CLICK O N M ODEL A ND SEE IF YOU CAN CREATE A COASTAL ENVIRONMENT. IN THE FOLLOWING D IAGRAM , U SE THE D IRECTION O F T HE W IND A ND W AVES T O L ABEL T HE L ONGSHORE C URRENT . T HEN , D RAW I N T HE A REA W HERE D EPOSITION I S GOING T O O CCUR U SING S HADING / DOTTED P ATTERN T O S HOW T HE S EDIMENT A CCUMULATION I N R ELATION T O T HE G ROIN ( J ETTY ). IN THE FOLLOWING D IAGRAM , U SE THE D IRECTION O F THE W IND AND W AVES TO LABEL THE L ONGSHORE CURRENT. THEN , D RAW IN THE A REA W HERE D EPOSITION I S G OING T O O CCUR U SING S HADING / DOTTED P ATTERN T O S HOW T HE S EDIMENT A CCUMULATION I N RELATION T O T HE O FFSHORE B REAKWATER .
BREAKWATER
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NAME
DATE
CLASS
Chapter 8 STUDY GUIDE
Text Pages 222–226
Ocean Shoreline
Each numbered list below gives some characteristics of one of the shoreline features in the box. Write the name of each shoreline feature above the correct list.
shoreline rocky shoreline 1.
beach barrier islands
longshore current
4. • rocks • cliffs • caves
2.
• sand deposits • separated from mainland • dunes 5.
• colliding waves • running water • parallel to shore
• smooth, gently sloping • sediment deposits • sands
3. • high tide • low tide • water’s edge A cause is something that makes something happen. An effect is what happens. Write the part of the statement that is the cause and the part that is the effect on the lines provided.
1. Shorelines change constantly because they experience the forces of tides, waves, and currents. cause: effect: 2. When constant wave motion bumps sand grains together, the corners of the sand become rounded. cause: effect: 3. The more energy a longshore current has, the more it will erode shoreline sediments. cause: effect: 4. Beaches have sand-sized particles because waves break rocks and seashells down. cause: effect:
36
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Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
NAME
DATE
CLASS
Chapter 10
Use with Section 3
ENRICHMENT
Ocean Shoreline
Shore Zone Features Many different features can develop from the deposition of sediments in a shor e zone. Study the following terms associated with shore erosion and deposition. Then use their descriptions to help you identify those featur es labeled in the illustration.
• headland—point of high land that juts out into the sea, a cape • bay—inlet of the sea that is usually smaller than a gulf • spit—load of sand that is deposited as soon as a longshore current turns into a bay • bay barrier—spit that extends across the mouth of a bay cutting the bay of f from the sea • lagoon—shallow pond that a bay can become when it is cut off from the sea Identify the features above on the illustration. Also identify the barrier island.
D F A
E
B B C
A.
D.
B.
E.
C.
F.
Page 34 of 45 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
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Test What You know About Wind, Waves… & WED Agents!
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Name _____________
Per _____
Base your answers to questions 1 through 3 on the passage and the cross section below. The passage describes the geologic history of the Pine Bush region near Albany, New York. The cross section shows the bedrock and overlying sediment along a southwest to northeast diagonal line through a portion of this are Location A shows an ancient buried stream channel and location B shows a large sand dune. The Pine Bush Region The Pine Bush region, just northwest of Albany, New York, is a 40-square mile area of sand dunes and wetlands covered by pitch pine trees and scrub oak bushes. During the Ordovician Period, this area was covered by a large sea. Layers of mud and sand deposited in this sea were compressed into shale and sandstone bedrock. During most of the Cenozoic Era, running water eroded stream channels into the bedrock. One of these buried channels is shown at location A in the cross section. Over the last one million years of the Cenozoic Era, this area was affected by glaciation. During the last major advance of glacial ice, soil and bedrock were eroded and later deposited as till (a mixture of boulders, pebbles, sand, and clay). About 20,000 years ago, the last glacier in New York State began to melt. The meltwater deposited pebbles and sand, forming the stratified drift. During the 5000 years it took to melt this glacier, the entire Pine Bush area became submerged under a large 350-foot-deep glacial lake called Lake Albany. Delta deposits of cobbles, pebbles, and sand formed along the lake shorelines, and beds of silt and clay were deposited farther into the lake. Lake Albany drained about 12,000 years ago, exposing the lake bottom. Wind erosion created the sand dunes that cover much of the Pine Bush area today.
1. How does the shape of the sand dune at location B provide evidence that the prevailing winds that formed this dune are blowing from the southwest? ____________________________________________________________________________________________ 2. Explain why the till layer is composed of unsorted sediment. ____________________________________________________________________________________________ 3. What evidence shown at location A suggests that the channel in the bedrock was eroded by running water? ____________________________________________________________________________________________ Page 41 of 45
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Name: __________________
Wind & how it weathers, erodes & deposits sediments
Page 1 of 45
Name ____________________________________ Date __________ Class ___________________
SECTION 8-6
SECTION SUMMARY
Wind Guide for Reading ◆ How does wind
cause erosion? ◆ What features result from deposition by wind?
Unit 3 Resources
W
Page 2 of 45
Science Explorer Earth Science
© Prentice-Hall, Inc.
58
ind by itself is the weakest agent of erosion. Yet wind can be a powerful force in shaping the land in areas where there are few plants to hold the soil in place. For example, in deserts few plants grow, and wind can easily move the grains of dry, light sand. The main way that wind causes erosion is by deflation. Geologists define deflation as the process by which wind removes surface materials. When wind blows over the land, it picks up particles of sediment. The stronger the wind, the larger the particles that it can pick up and move through the air. Particles that are too heavy to be picked up might skip or bounce for a short distance. Strong winds can even roll heavier sediment particles over the ground. Deflation does not usually have a great effect on the land. In deserts, though, deflation can sometimes create an area of rock fragments called desert pavement. There, wind has blown away the smaller sediment. All that remains are rocky materials that are too large and heavy to be moved by wind. Abrasion by wind-carried sand can polish rock, but it causes little erosion. At one time, geologists thought such abrasion cut the stone shapes seen in deserts. But evidence now shows that most desert landforms are the result of weathering and water erosion. All sediment picked up by wind eventually falls to the ground. This happens when wind slows down or some obstacle, such as a boulder or clump of grass, traps the windblown sand and other sediment. Wind erosion and deposition may form sand dunes and loess deposits. A sand dune is a deposit of wind-blown sand. When wind carrying sand strikes an obstacle, the result is usually a sand dune. Sand dunes can be seen on beaches and in deserts where wind-blown sediment has built up. Sand dunes come in many shapes and sizes. Sand dunes often move over time. Plant roots can help anchor a sand dune in one place. Sand dunes are most often made of the coarser sediments carried by wind. The finer sediments are often deposited in layers far from their source. This fine, wind-deposited sediment is loess. Large loess deposits are found in central China and in such states as Nebraska, South Dakota, Iowa, Missouri, and Illinois. Loess helps form fertile soil.
The desert landscape has many interesting geologic features. How do the agents of WED create this landscape?
Weathering & Erosion By Wind • Dry Climates (soil made of dry & loose sand, silt, & clay which are easily carried by wind) • Mechanical weathering by ABRASION (wind carries sediments and blows them against rocks – like sandpaper) • Sediments eroded by wind have a frosted appearance
Weathering & Erosion By Wind
Note…no solution…WHY?
• VENTIFACTS – larger rocks in arid regions shaped by wind-blown sand hitting into and abrading them. They will have a pitted surface.
– Sometimes, the wind direction varies and the rocks get abraded on all sides. – Sometimes, the sides of the rocks facing the prevailing wind are worn smooth over time and have a distinct angled side.
SAND DUNES
VIF!!!!!
• Large piles of sand deposited by wind – Usually start piling up against rocks, bushes, clumps of grass, etc…
• Side of the dune facing the wind (WINDWARD SIDE) has a long gentle slope • Side opposite (LEEWARD SIDE) is a short, steep slope – also known as the “slip face” (like if you tried to walk down it you’d slip because it’s steep…)
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You need to be able to draw the dune if given the wind direction and the wind if given the dune shape!
DEFLATION VIF!!!!
• Wind removes the top layer of soil, clay and silt, causing the ground surface to lower over time and leaving behind courser sediments. – The soil “DEFLATES” (like a bicycle tire) and there can be small depressions or “blowouts” with larger rocks creating a “pavement”. That’s when the deflation process will end as those sediments are too large to be moved by the wind.
Erosion by Wind
Deflation “pits”
• If soil is not “held down” via plant roots and sufficient moisture content, the soil can be eroded away easily by wind. – The removal of soil makes the farmland unusable. – This can create very bad dust storms when the winds increase in velocity. – This created the dustbowl in the plains states during the 1930’s (Great Depression)
Desert pavement
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Erosion by Wind • Today, a common place people experience dust storms is in Phoenix and Tuscon, Arizona. • These storms are called Haboobs and occur during the dry summers in the southwest. • They can be very scary and dangerous – especially for drivers!
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Waves, longshore currents & Shoreline Erosional & Depositional Features Page 11 of 45
Name ____________________________________ Date __________ Class ___________________
SECTION 8-5
SECTION SUMMARY
Waves Guide for Reading ◆ What gives ocean
waves their energy? ◆ How do ocean waves shape a coast?
Unit 3 Resources
O
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Science Explorer Earth Science
© Prentice-Hall, Inc.
54
cean waves contain energy. The energy in waves comes from wind that blows across the water’s surface. As the wind makes contact with the water, some of its energy transfers to the water. The energy of a wave causes water particles to move up and down as the wave goes by. But the water particles themselves don’t move forward. Only the form of the wave moves. A wave changes as it approaches land. In the shallow water near the shore, the water actually does move forward with the wave. This forward-moving water provides the force that shapes the coast. Waves are a major force of erosion along coasts. One way waves erode is by impact. The energy in waves can break apart rocks and make cracks in rocks larger. Waves also erode by abrasion. As a wave approaches shallow water, it picks up sediment. When the wave hits land, the sediment wears away rock. Waves coming to shore gradually change direction as different parts of a wave begin to drag on the bottom. For instance, incoming waves bend as they approach a headland. A headland is a part of the shore that sticks out into the ocean. The waves concentrate their energy on the headland, and eventually wear it down, evening out the shore. When waves hit a steep, rocky coast, they strike the area again and again. Along a steep coast, waves will erode the base of the land, especially where the rock is softer. Over time the waves may erode a hollow area, called a sea cave. Eventually, waves may erode the base of the land so much that the rock above collapses. The result is a wave-cut cliff. Other landforms created by wave erosion include sea arches and sea stacks. Waves not only erode the land, they also deposit sediment. Waves shape the coast through both erosion and deposition. Deposition occurs when waves slow down and the water drops its sediment. As waves reach the shore, they drop the sediment they carry, creating a beach. A beach is an area of wave-washed sediment along a coast. Most beach sand comes from rivers that carry eroded particles of rock into the ocean. Some beaches are made of small fragments of coral or sea shells piled up by wave action. The sediment on a beach usually moves after it has been deposited. Waves usually hit a beach at an angle, creating a current that runs parallel to the coastline. As repeated waves hit the beach, some of the sediment moves down the beach with the current, in a process called longshore drift. One result of longhore drift is the formation of a spit, a beach that projects like a finger into the water. Incoming waves carrying sand may build up sandbars, long ridges of sand parallel to the shore. A barrier beach is similar to a sandbar, but a barrier beach forms when storm waves pile up sand above sea level. Barrier beaches are found in many places along the Atlantic coast of the United States.
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What Creates Waves? • Wind blowing the surface of the water causing it to “pile up” • HEIGHT depends on 3 things: 1 – wind speed 2 – wind duration - length of time the wind blows over the water 2 – distance the wind blows over the open water – “FETCH”
Why is the wave height so great in the Southern Ocean?
Wave Features • Waves cause surface water to rise & fall Top of the wave = CREST • Bottom of wave = TROUGH • WAVE HEIGHT is the difference between the crest and trough • WAVE LENGTH is the distance from one crest to the next crest (or trough to trough) • AMPLITUDE the distance from the baseline (sea level) to the top of the crest or bottom of the trough.
• Ocean waves transmit the energy that the wind transferred through them. The water molecules don’t move through the ocean, just the energy!
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Waves in Shallow Water • BREAKERS – waves that enter shallow water, slow down & “break” – The bottom of the wave “scrapes” along the bottom of ocean & slows down due to friction, this reduces its wavelength. – The reduction in wavelength (horizontal) increases the wave height (vertical) – (Conservation of energy.) – The crest (top) of the wave continues forward at the same speed & falls over onto the beach. (The crest is not moving faster, it just appears to move faster because the bottom part of the wave is moving slower!!!)
As waves enter shallower water (less than half of the wavelength), their wavelength decreases which causes their height to increase!
As waves enter shallower water (less than half of the wavelength), their wavelength decreases which causes their height to increase!
Waves in Shallow Water • Waves always approach the shoreline at an angle • As the wave enters water, the part of the wave that “hits” the shallow shoreline first, slows down (due to friction) and the part of the wave that isn’t hitting the shoreline keeps moving at the same speed. • The wave crest direction “bends” due to the difference in speed. • Shoreline waves REFRACT & hit the shore almost parallel to shore BUT NOT PARALLEL!!!!!
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CURRENTS • All of this wave physics and refraction leads us to what we really NEED to know… • Phenomena ---Ever notice how when you get out of the ocean after swimming you’re farther down the beach from where you went in?!?!
• VIF!!! LONGSHORE CURRENTS – move parallel to shoreline & carry sand down the beach (erosion) • Their direction is determined by examining the direction of the wave crests that are hitting the shore when looking from above.
Longshore Current: VIF!!!! transportation of sediments parallel to the beach…this is the current that can transport you parallel to the beach as well!
• SWASH – water moving ONTO the beach • BACKWASH – water moving back off beach – Pulls sand from the beach into the water – UNDERTOW – a strong backwash – very dangerous for Ocean small children!
Which direction is the longshore current moving in this photo?
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Human’s build Jetties, Groins and Breakwaters to prevent erosion and build up the width of beaches by forcing deposition. Which direction is the longshore current moving in this photo? Draw an arrow.
FYI & Safety! • RIP CURRENTS – very strong currents that move OUTWARD from the shore • The geology of the area under the water creates them. • The WORST thing to do if caught in a rip current is to panic & try to swim directly to shore! The current is too strong & you will fatigue and drown! Swim across the current (parallel to the shore) to escape the current!
FYI - Littoral current is another name for longshore current…
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SHORELINE FEATURES Very energetic waves easily erode soft rocks found along deep water shorelines Sea Cliffs, Sea Arches, Sea Caves, and Sea Stacks are commonly found off the coast of Maine, California, Oregon, Hawaii, Canada and Australia. Pick out the headlands, cliffs, arches, caves and stacks on the following slides!!!!
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Haystack Rock, OR
People!!!
Less energetic waves deposit a lot of sediments along the eastern shores of the USA! • Longshore currents deposit large amounts of sediment over time. • A SANDBAR is formed when ocean currents deposit sand near the shore. Sandbars may take many different forms… • 1) BARRIER ISLANDS are LARGE sandbars parallel to shore (Fire Island, NY & the Outer Banks, NC)
– Barrier islands protect the shoreline from the full strength of waves – These shoreline features are NOT permanent! They are constantly being built up and destroyed by waves! – Most of the Eastern Coast of the USA has Barrier Islands and flat sandy beaches.
Barrier Islands… think Fire Island, Long Island and Outer Banks, No. Carolina
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Spit: sandbar that is connected to land on one side of a bay
Bay: indentation of shoreline creating a body of water connected to an ocean
Baymouth Bar – a sandbar (overgrown spit) that completely closes access to a bay, thus closing it off from the main body of water creating a lagoon
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Think – San Francisco Bay…Hudson Bay…
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NAME:_______________________________________________
Date:_________________
Per #:_______
Investigating Coastal Processes GO TO SITE: https://ees.as.uky.edu/sites/default/files/elearning/module14swf.swf R EAD THE O PENING PARAGRAPH. C LICK O N THE O VERVIEW LINK B EACH A NATOMY:
T ASK # 1: L ABEL THE M AIN COMPONENTS O F A BEACH SYSTEM
C LICK O N THE RIGHT A RROW N EXT TO B EACH A NATOMY, IT SHOULD N OW SAY W AVE ANATOMY. P RESS THE START BUTTON TO SEE BREAKERS F ORM . P RESS I T S EVERAL T IME T O S EE T HE P ROCESS R EPEAT F OR A B ETTER U NDERSTANDING O F I T . T ASK # 2: D EFINE THE KEY TERMS O F THE A NATOMY O F A W AVE – U SE THE BLACK ARROWS AT THE FAR FIGHT SCROLL U P A ND D OWN TO R EAD T HE I NFORMATION Crest: Trough: Wave Height: Page 26 of 45
Wavelength: Amplitude: Breaker: T ASK#3: C LICK THE RIGHT A RROW AFTER W AVE ANATOMY. IT SHOULD N OW SAY W AVE M OTION . R EAD THE PARAGRAPH AND F OLLOW T HE D IRECTIONS . Waves break because the top of the wave orbitals keep moving at the ______________________________________, while the bottom of the wave oribitals __________________________ due to the friction from the ocean floor. T ASK # 4: CLICK O N THE RIGHT ARROW A FTER W AVE M OTION . IT SHOULD NOW SAY W AVE REFRACTION . R EAD THE PARAGRAPH A ND A NSWER T HE F OLLOWING Q UESTIONS . Why do waves refract inward towards the beach?_________________________________________________________ __________________________________________________________________________________________________ What are the names of the 2 structures that humans build that make the water more shallow and slows down the waves? ______________________ and _________________________ T ASK#5: CLICK O N THE RIGHT ARROW AFTER W AVE REFRACTION . IT SHOULD SAY LONGSHORE CURRENT. W ATCH THE ANIMATION A ND R EAD T HE P ARAGRAPH . A NSWER T HE F OLLOWING Q UESTION .
Define Longshore current: __________________________________________________________________________ _________________________________________________________________________________________________ Does the longshore current run in the same direction or opposite direction as the incoming wave crests? ______________________________________________________________ Task #6: CLICK O N THE RIGHT ARROW A FTER LONGSHORE CURRENT. IT SHOULD SAY RIP CURRENTS. W ATCH THE ANIMATION A ND R EAD T HE P ARAGRAPH . A NSWER T HE F OLLOWING Q UESTION .
What would you do to escape a rip current?_____________________________________________________________
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T ASK # 7: CLICK O N THE RIGHT ARROW A FTER RIP CURRENTS. IT SHOULD SAY COASTAL D EPOSITIONS. W ATCH THE A NIMATION AND READ T HE P ARAGRAPH . L ABEL THE FOLLOWING O N THE D IAGRAM : W AVE CREST, LONGSHORE CURRENT, AREA O F D EPOSITION (SEVERAL), AREA O F EROSION (SEVERAL). T ASK # 8: C LICK O N THE RIGHT A RROW A FTER C OASTAL D EPOSITION. R EAD A BOUT H OW A SEA STACK COULD BE FORMED FROM A H EADLAND . T ASK # 9: CLICK O N THE RIGHT ARROW A FTER COASTAL DEPOSITIONS. IT SHOULD SAY COASTAL EROSIONS LANDFORMS. WATCH T HE A NIMATION A ND R EAD T HE P ARAGRAPH . C LICK O N T HE R IGHT A RROW A GAIN . I T S HOULD S AY C OASTAL E ROSION : CONTROLS . C LICK O N E ACH O F T HE C ONTROLS T O S EE H OW T HEY A FFECT D EPOSITION .
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T ASK # 10: FINALLY, CLICK O N M ODEL A ND SEE IF YOU CAN CREATE A COASTAL ENVIRONMENT. IN THE FOLLOWING D IAGRAM , U SE THE D IRECTION O F T HE W IND A ND W AVES T O L ABEL T HE L ONGSHORE C URRENT . T HEN , D RAW I N T HE A REA W HERE D EPOSITION I S GOING T O O CCUR U SING S HADING / DOTTED P ATTERN T O S HOW T HE S EDIMENT A CCUMULATION I N R ELATION T O T HE G ROIN ( J ETTY ). IN THE FOLLOWING D IAGRAM , U SE THE D IRECTION O F THE W IND AND W AVES TO LABEL THE L ONGSHORE CURRENT. THEN , D RAW IN THE A REA W HERE D EPOSITION I S G OING T O O CCUR U SING S HADING / DOTTED P ATTERN T O S HOW T HE S EDIMENT A CCUMULATION I N RELATION T O T HE O FFSHORE B REAKWATER .
BREAKWATER
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NAME
DATE
CLASS
Chapter 8 STUDY GUIDE
Text Pages 222–226
Ocean Shoreline
Each numbered list below gives some characteristics of one of the shoreline features in the box. Write the name of each shoreline feature above the correct list.
shoreline rocky shoreline 1.
beach barrier islands
longshore current
4. • rocks • cliffs • caves
2.
• sand deposits • separated from mainland • dunes 5.
• colliding waves • running water • parallel to shore
• smooth, gently sloping • sediment deposits • sands
3. • high tide • low tide • water’s edge A cause is something that makes something happen. An effect is what happens. Write the part of the statement that is the cause and the part that is the effect on the lines provided.
1. Shorelines change constantly because they experience the forces of tides, waves, and currents. cause: effect: 2. When constant wave motion bumps sand grains together, the corners of the sand become rounded. cause: effect: 3. The more energy a longshore current has, the more it will erode shoreline sediments. cause: effect: 4. Beaches have sand-sized particles because waves break rocks and seashells down. cause: effect:
36
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Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
NAME
DATE
CLASS
Chapter 10
Use with Section 3
ENRICHMENT
Ocean Shoreline
Shore Zone Features Many different features can develop from the deposition of sediments in a shor e zone. Study the following terms associated with shore erosion and deposition. Then use their descriptions to help you identify those featur es labeled in the illustration.
• headland—point of high land that juts out into the sea, a cape • bay—inlet of the sea that is usually smaller than a gulf • spit—load of sand that is deposited as soon as a longshore current turns into a bay • bay barrier—spit that extends across the mouth of a bay cutting the bay of f from the sea • lagoon—shallow pond that a bay can become when it is cut off from the sea Identify the features above on the illustration. Also identify the barrier island.
D F A
E
B B C
A.
D.
B.
E.
C.
F.
Page 34 of 45 Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
29
Test What You know About Wind, Waves… & WED Agents!
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Name _____________
Per _____
Base your answers to questions 1 through 3 on the passage and the cross section below. The passage describes the geologic history of the Pine Bush region near Albany, New York. The cross section shows the bedrock and overlying sediment along a southwest to northeast diagonal line through a portion of this are Location A shows an ancient buried stream channel and location B shows a large sand dune. The Pine Bush Region The Pine Bush region, just northwest of Albany, New York, is a 40-square mile area of sand dunes and wetlands covered by pitch pine trees and scrub oak bushes. During the Ordovician Period, this area was covered by a large sea. Layers of mud and sand deposited in this sea were compressed into shale and sandstone bedrock. During most of the Cenozoic Era, running water eroded stream channels into the bedrock. One of these buried channels is shown at location A in the cross section. Over the last one million years of the Cenozoic Era, this area was affected by glaciation. During the last major advance of glacial ice, soil and bedrock were eroded and later deposited as till (a mixture of boulders, pebbles, sand, and clay). About 20,000 years ago, the last glacier in New York State began to melt. The meltwater deposited pebbles and sand, forming the stratified drift. During the 5000 years it took to melt this glacier, the entire Pine Bush area became submerged under a large 350-foot-deep glacial lake called Lake Albany. Delta deposits of cobbles, pebbles, and sand formed along the lake shorelines, and beds of silt and clay were deposited farther into the lake. Lake Albany drained about 12,000 years ago, exposing the lake bottom. Wind erosion created the sand dunes that cover much of the Pine Bush area today.
1. How does the shape of the sand dune at location B provide evidence that the prevailing winds that formed this dune are blowing from the southwest? ____________________________________________________________________________________________ 2. Explain why the till layer is composed of unsorted sediment. ____________________________________________________________________________________________ 3. What evidence shown at location A suggests that the channel in the bedrock was eroded by running water? ____________________________________________________________________________________________ Page 41 of 45
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