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Chapter 7: Erosion and Deposition

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1 Chapter 7: Erosion and Deposition
7.1: Forces wear down and build up Earth’s surface 7.2: Moving water shapes land 7.3: Waves and wind shape land 7.4: Glaciers carve land and move sediments

2 7.3: Waves and wind shape land
Before, you learned: Stream systems shape Earth’s surface Groundwater creates caverns and sinkholes Now, you will learn: How wave currents shape shorelines How wind shapes land Book, p.158: Pillars of Rock, Port Campbell, Australia: Why do you think these are left over from large areas of rock? The pillars are made of hard rock that was among softer or fractured rock that was easier to weather and disintegrate

3 Waves and currents shape shorelines
Port Campbell pillars formed by movement of water Continuous action of waves breaking against the cliffs 2 cm/year, and still eroding Force of wave: powered by wind, can wear away rocks and transport sand Force of wind: can change the look of land

4 Shorelines Can be flat, low, high, steep, rocky, sandy…
High rock cliff: waves crash and wear away bottom rocks Low coastlines build up Similar to when a stream flows into an ocean or lake, sediment is deposited near its mouth This sediment mixes with sediment from waves beating against the coast, building up beaches Describe movement of sediment and water along the shore: Longshore drift Longshore current

5 Shorelines – Longshore drift
Longshore drift: zigzag movement of sand along a beach Wind blows across water and may hit the shoreline at an angle Carries sand to shore, and gravity pulls the water and sand back out to the water The sand gradually moves down the beach Moves large amounts of sand along a beach: shrink/grow

6 Shorelines – Longshore current
Longshore current: movement of water along a shore as waves strike the shore at an angle Direction may change from day to day as wave direction changes

7 Oceans, aside Ocean waves are a movement of energy, not water
A cork in water impacted by a wave moves - it rises and falls on the wave but does not move forward Water waves move energy, not material A message in a bottle thrown to sea may arrive cross the sea by currents, rather than waves

8 Sandbars and Barrier Islands
Longshore currents can deposit sand along shorelines This sand builds up to form sandbars A ridge of sand built up by the action of waves and currents If the sandbar is built up above the water’s surface and is joined to the land, it is called a “spit” Strong longshore currents that mostly move in one direction over time build up the sandbar into barrier islands A long narrow island that develops parallel to a coast Forms a barrier between the ocean waves and the shore of the mainland Common along gently sloping coasts: New Jersey, North Carolina, Gulf of Mexico Constantly change shape


10 Wind shapes land Sand dunes…far from a desert or ocean!
Created by wind: Dune: a mount of sand built up by wind Like water, wind can transport and deposit sediment Especially powerful in dry regions where soil is not held in place (few plants) Near Lake Michigan

11 Wind Shapes Land Dune formation:
Strong wind picks up and transports sand particles – deposits the sand which builds to dunes Can start as a ripple then grow larger Can form as wind-carried sand settles around a rock, log, or other obstacle Need: strong winds AND constant supply of loose sand Vary in size an d shape up to 300 meters (1000 ft), curved, straight, mounds Typically have a gentle slope facing the wind, and steep on the other side



14 Loess Wind also changes soil by depositing dust
Loess: deposits of fine wind-blown sediment Can build up over thousands or millions of years Forms good soil for growing crops Some deposits 300 meters thick! Ex: China: deposits are 2 million years old Central U.S.: between 8-30 m ( ft) deep

15 Desert Pavement Wind can also remove dust
It blows away sand, silt, and gravel, leaving behind a layer of stones and gravel Called “desert pavement” because it looks like a cobblestone pavement What remains is too heavy to be picked up by wind

16 Coastline video: http://scienceblips. dailyradar

17 Snow Line Elevation and Latitude p.251

18 Mount kenya is very close to the equator
Mount kenya is very close to the equator. Estimate the snow line elevation on mount kenya. Mount rainier is at 47 degrees north latitude and is 4389 meters tall. Can there be glaciers on mount rainier? If so, estimate the elevation above which the glaciers form. Mount washington in new hampshire is at 45 degrees north latitude and is 1917 meters tall. Can there be glaciers on mount washington? If so, estimate theeir lowest elevation. Challenge: temperatures are hotter at the equator than at 28 degrees north latitude. Why is the snow line lower at the equator in Ecuador?

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