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Chapter 9 Erosion PowerPoint

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Chapter 9 Erosion PowerPoint

  1. 1. Wearing Down and Building Up •Weathering breaks down earth’s surface into sediments. “Breaks” •Erosion is when sediments are transported. “Takes” •Deposition is when sediments “settle out” or are “dropped” by whatever is carrying them. This can build up landforms or fill in areas. “Makes” •Principle of Uniformitarianism- Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface today and in the past.
  2. 2. • Have you ever seen a “muddy” stream or river? • The water appears “muddy” because it is carrying small particles of sediment! Erosion from running water is at work!
  3. 3. Runoff and Erosion •After it rains, some of the water that does not soak into the ground becomes runoff. •More runoff = more erosion.
  4. 4. Streams and Rivers •Streams and creeks form from runoff. •Rivers form when streams come together. •A tributary is a stream or river that flows (along with any sediment it is carrying) into a larger river. •Exs. Pine creek is a tributary to the Allegheny river. •As water moves through streams and rivers, it picks up sediment and carries it! Erosion is happening!
  5. 5. Today you are going on a river trip! You are going to follow a river from start to finish and discover many things along the way! Pick your boat of choice:
  6. 6. River Erosion •You start your journey at the river’s source which is often a steep mountain stream. You will end your journey at the river’s mouth which is when it reaches the sea.
  7. 7. River Erosion •Wow! At the river’s source, you notice the water is fast flowing and follows a straight and narrow course. You barely have to paddle! •It erodes deep into the mountain, eventually forming a V-shaped valley. As it cuts into the earth, the water continues to pick up sediment.
  8. 8. River Erosion • You are at the bottom of the mountain and you notice a fan- shaped deposit. You realize that this must be an Alluvial fan. • When a stream comes to the bottom of a mountain water slows down, spreads out, and drops or deposits its sediment in a fan shape.
  9. 9. River Erosion •As the river flows, you notice there are deep canyons, gorges and waterfalls carved by the river. •The “Grand Canyon” was slowly carved out of the Colorado Plateau by the Colorado River over millions of years. Grand Canyon of PA
  10. 10. River Erosion •Waterfalls are created when softer rock erodes before overlying harder rock, creating a steep drop. •Be careful, rocks that have broken off create rapids! World Record Holder-Costa Rica
  11. 11. Erosion by Rivers •The paddling is getting tough!! Now you are lower on the river’s course and closer to the sea, you notice it slows down and spreads out. It is no longer fast and narrow. It erodes a wide area on its sides called a flood plain. This is where water goes when it overflows the river banks. •You notice that the land along the flood plain is flat and you notice a lot of farms so it must be very fertile. •Although land along a floodplain may be appealing, what are some potential problems with living along it?
  12. 12. Erosion by Rivers • You are moving so slowly and you notice you are no longer taking a straight path! Instead, the river meanders or forms loop like bends. •You move to the outside of the curve because you notice the water moves faster on the outside and slower on the inside curve. •Therefore erosion happens along the outside and where the water is slowing down, along the inside, sediment that the water is carrying gets deposited and forms cute little beaches! •Yum! You stop along one of these beaches for a snack!
  13. 13. Erosion by Rivers •As you are moving, you notice a strange C- shaped lake! •When meanders get too curved, the river is able to “break through” and takes a straight course again. The meander gets cutoff as sediment builds up. This is called an oxbow lake. The lake looks like a C!
  14. 14. Deposits by Rivers •You made it! You have reached the ocean! •Sediment that is eroded away by rivers and streams is deposited at the river’s mouth as a river slows down forming a landform called a delta. •Delta -Rivers slow as they meet the sea. The sediment is deposited which forms new land. They take on a triangular shape and are named after the Greek letter ∆. •The city of New Orleans is built on land created by a river!
  15. 15. Groundwater Erosion •Rain water that does not evaporate or become runoff soaks into the ground and is called groundwater. •Groundwater can be in the form of underwater streams but most of the time it is held in the pore spaces of rocks.
  16. 16. Groundwater Erosion •Carbon dioxide can dissolve in water making it acidic. This acidic water can weather and dissolve limestone underground forming a cave. •Once the groundwater in the cave lowers, the cave is filled with air. •When water containing dissolved limestone (main mineral is calcite) drips from the ceiling and hits the air, the water evaporates and leaves behind the limestone again forming a Stalactite. •When this water drips to the floor it builds up a Stalagmite.
  17. 17. Ceiling - Stalactite Ground - Stalagmite
  18. 18. Groundwater Erosion • Karst topography is found in many parts of the United States where the bedrock is made up of layers of limestone that have been eroded by acidic water. • Karst topography has caves and sinkholes (sinkholes are caves where the roof has collapsed)
  19. 19. Glaciers – “Rivers of Ice” •Glacier-A large, slow moving mass of ice. Glaciers form when more snow falls each year than melts so it builds up.
  20. 20. How Glaciers Form and Move •A continental glacier is a glacier that covers much of a continent or large island. Antarctica and Greenland are large continental glaciers! •Continental glaciers move by spreading outwards in all directions towards the sea.
  21. 21. How Glaciers Form and Move •The last Ice Age ended around 12,000 years ago. Most of Earth’s water was in the form of ice. During the last ice age, a continental glacier covered most of northern North America. •Most of the land and water were covered under an ice sheet that was 2.5 miles thick in some places.
  22. 22. Valley Glaciers •Valley Glaciers form when snow and ice pile up high in the mountains. The ice slowly begins to move downward because of gravity. •Ex. Alaska and Glacier National Park in Montana
  23. 23. How Glaciers Form and Move •Like the force of gravity and running water, glaciers too cause both erosion and depositional features which scar and shape the land!
  24. 24. Glacial Erosion Features-How Glaciers shape the land **Remember, erosion is the transportation of sediment** 1. As a glacier moves, plucking breaks and picks up pieces of bedrock from the ground and carries them.
  25. 25. Glacial Erosion Features 2. V-Shaped valleys become U-Shaped as glaciers erode old river valleys. Glaciers can also carve a mountain peak into a sharp horn or sharp peak and leave bowl shaped depressions along mountains called cirques.
  26. 26. Glacial Erosion Features 3. Glaciers also carved depressions in the land which can fill with water to create lakes (ex. Great Lakes)
  27. 27. Glacial Erosion Features 4. As glaciers move across the land, they scratch the bedrock (remember they are carrying rocks). These are known as glacial striations.
  28. 28. Glacial Deposition Features *Remember, deposition is the dropping of sediment.* 1. As glaciers melt and retreat, they deposit the sediment that they were carrying which is a mixture of clay and boulders known as Till. How did this rock get here? 2. Many big boulders were dropped as the ice melted away at the end of the last ice age. These big, out of place boulders are known as glacial erratics. Glaciers can move huge rocks that wind or water could not move!
  29. 29. Glacial Deposition 3. The very end of the glacier pushes along a lot of rocks, so when it quits moving and begins to melt, it leaves the till in a pile. This is known as a terminal moraine.
  30. 30. Glacial Deposition •Moraine State Park, about 40 minutes North of Shaler, is the southernmost point in Pennsylvania that the glaciers reached during the last ice age. •The soil in the park is full of boulders and a mixture of rock that was stuck in the ice as it moved across Canada!
  31. 31. Glacial Deposition • Lateral moraines are parallel ridges of sediment deposited along the sides of a glacier.
  32. 32. Glacial Deposition Features 4. Often when glaciers retreat (begin to melt) they leave behind chunks of ice. These melt and create lakes called kettle lakes. Ex. Conneaut Lake in PA & Walden Pond in Concord, Massachusetts!
  33. 33. Erosion by Waves •Many ocean waves are caused by wind and can have tremendous power (we will talk about tides later this year which are caused by something else!). Some of the world’s biggest storms happen at sea!
  34. 34. Erosion by Waves •Due to constant erosion by wave action, there are many unique landforms found along the edges of the continents.
  35. 35. Erosion by Waves •Waves shape the coast through weathering (abrasion), erosion, and deposition. Waves carry sand and gravel which wear away rock like sandpaper breaking it down, transporting the sediment, and depositing it.
  36. 36. Erosion by Waves •Weathering, erosion, and deposition creates a variety of unique landforms along a coast. 1. Wave-Cut Cliffs 2. Sea Caves 3. Sea Stack 4. Sea Arch 5. Headland-land that stands out from the coast because it is made of erosion- resistant rock.
  37. 37. Deposits by Waves •Waves shape a coast when they deposit sediment, forming coastal features such as beaches, spits, and barrier beaches. 1. Beaches 2. Spit 3. Sandbar 4. Barrier Beach- large sandbar Ocean City MD and Outer Banks, NC and Cape Cod
  38. 38. Outer Banks, NC Barrier Beach Ocean City, MD Spit Sandbar
  39. 39. Deposits by Waves •Beaches are constantly being moved around and reshaped by a process known as longshore drift. •Because waves often hit the shore at an angle, then move straight back due to gravity, sand often travels down a beach in a zig-zag manner.
  40. 40. Deposits by Waves •Beaches are constantly being changed by longshore drift. •Sometimes in heavily developed areas beaches have to have sand added to them or have structures called jetties built to reduce erosion.
  41. 41. Deposits by Waves •You can tell a lot about a beach by examining its grains of sand. •What do the shape of the sand grains tell you? How much weathering the grains have been exposed to. •What do the different colors in sand tell you? What minerals/materials the beach is made from.
  42. 42. How Wind Causes Erosion •Wind erosion usually occurs in dry areas where there is little vegetation to keep sediment in place. •Ex. deserts and recently plowed farmland. •Wind erosion led to the Dust Bowl!
  43. 43. How Wind Causes Erosion •Wind wears down rock, kind of like a natural sandblasting. This is known as abrasion.
  44. 44. Wind Deposition •Wind erosion and deposition may form giant piles of sand dunes. Erg Chebbi, Morocco
  45. 45. Mass Movement- Gravity •Mass Movement is when rock is eroded by gravity. •Gravity pulls everything toward the center of the earth. •Mass movement can be triggered by earthquakes, volcanoes, heavy rainfall, etc. •The different types of mass movement include landslides, slump, creep and mudflows. K1qY8nPqcCw
  46. 46. Landslides - Problems Around Pittsburgh •Every year, tumbling rocks called landslides along Route 28 near Harmarville cause nightmares for motorists! •Also a few years ago a landslide caused Rt 65 to close for weeks after the construction of a new Walmart destabilized the land! •Pittsburgh is especially prone to landslides and mudslides because our local rocks contain a lot of clay so they easily crumble when wet.
  47. 47. Mudslides •Mudflows or mudslides - can occur when loose sediment becomes drenched after heavy rainfall. (Hurricanes) •Can also happen around volcanoes (when snow and ice melt rapidly after a volcanic eruption.)
  48. 48. Mudslide from the May 1980 eruption of Mount St. Helens.

Editor's Notes

  • Picture of the point taken by a former student. Different colors of the river showing the different types/amounts of sediment the Mon and Allegheny carry.
  • Pink Sand, BermudaGreen and Black Sand Hawaii