Presentation on theme: "23.4 Glaciers and Wind This valley glacier has bands that look like ripples. The dark bands, which include rock debris, show the glacier’s slower growth."— Presentation transcript:
23.4 Glaciers and Wind This valley glacier has bands that look like ripples. The dark bands, which include rock debris, show the glacier’s slower growth in summer. The light bands form in the winter. Red Sea
23.4 Glaciers and Wind How do glaciers form? How Glaciers Form and Move Glaciers form in places where more snow falls than melts or sublimates.
23.4 Glaciers and Wind As the layers of snow pile up, the weight on the underlying snow increases, and glacial ice is formed. The force of gravity pulls the ice downhill. Like a river, a glacier flows fastest in the middle and slowest along the sides. How Glaciers Form and Move
23.4 Glaciers and Wind There are two types of glaciers. A continental glacier is a thick sheet of ice that covers a huge area, such as a continent or large island. A glacier that occurs in a high mountain valley is called a valley glacier. How Glaciers Form and Move
23.4 Glaciers and Wind What landscape features are created by glacial erosion and deposition? Glacial Erosion and Deposition Glaciers cause many distinctive features in the landscape, including cirques, horns, U- shaped valleys, and glacial lakes. When a glacier melts, it deposits its load of sediment, creating a variety of landforms.
23.4 Glaciers and Wind Though glaciers move much more slowly than rivers, they are very effective at eroding and depositing sediment. Glaciers erode rock through abrasion and plucking. In plucking, glacial ice widens cracks in bedrock beneath the glacier. Pieces of loosened rock are then frozen to the bottom of the glacier, which carries them away. The pieces of rock that are stuck to the bottom and sides of the glacier act like sandpaper, scraping the bedrock and soil under it and along its sides. Glacial Erosion and Deposition
23.4 Glaciers and Wind As a glacier moves downhill, it loosens and lifts pieces of rock from the ground underneath. Glacial Erosion and Deposition Glacial ice
23.4 Glaciers and Wind Features Formed by Glacial Erosion A glacier can carve large bowl-shaped valleys, called cirques, out of a mountainside. If several cirques form close together, a ridge may be left between them. If several ridges connect to form a pyramid-shaped peak, the peak is called a horn. Glacial Erosion and Deposition
23.4 Glaciers and Wind The distinctive landscape near Mount Robson in British Columbia, Canada, was formed by glaciers. Glacial Erosion and Deposition
23.4 Glaciers and Wind Glaciers also widen and deepen the valleys through which they flow. When glaciers flow through V-shaped valleys, they widen them into U-shaped valleys. Glacial valleys are U-shaped because the moving ice scours the entire valley. Glacial Erosion and Deposition
23.4 Glaciers and Wind Glaciers can carve out large U-shaped valleys, such as this one in Glacier National Park, Montana. Glacial Erosion and Deposition
23.4 Glaciers and Wind Unlike valley glaciers, continental glaciers tend to level large surface areas through the scraping and grinding of thick ice. Continental glaciers can enlarge and deepen natural depressions in the surface. These depressions then fill with water when the glaciers retreat. Glacial Erosion and Deposition
23.4 Glaciers and Wind Features Formed by Glacial Deposition Glacial sediment is called till. Till is an unsorted mixture of sediment containing fragments of many sizes. Glaciers deposit till as they melt. The till forms moraines, mounds of sediment at the downhill end of the glacier and along its sides. Glacial Erosion and Deposition
23.4 Glaciers and Wind What are the effects of wind erosion and deposition? Wind Erosion and Deposition Wind erodes the land by deflation and abrasion. Features deposited by wind include sand dunes and loess deposits.
23.4 Glaciers and Wind Wind can also cause erosion and deposition. The speed of the wind determines the size of the materials it carries. A constant, strong wind can produce a large cloud of dust or sand. Wind Erosion and Deposition
23.4 Glaciers and Wind Most wind erosion occurs in dry areas, such as deserts. Wind erosion also occurs in areas where drought has caused the ground to dry out and the soil is not held in place by plants. Wind Erosion and Deposition
23.4 Glaciers and Wind How Wind Causes Erosion The wind moves small particles such as sand grains in a series of leaps called saltation. Wind lifts sand grains a short distance into the air. Gravity pulls the grains back down to the ground, where they collide with and loosen other grains. The result is that the sand grains leap-frog along. Wind Erosion and Deposition
23.4 Glaciers and Wind Wind erosion moves particles of different sizes. Wind Erosion and Deposition Direction of Wind Large particles pushed by wind Sand grains moving by saltation Dust particles suspended in wind
23.4 Glaciers and Wind The process of deflation occurs when wind picks up and carries away loose surface material. Over time, the surface of the ground is lowered. Larger rocks are left behind, forming a rocky surface that covers much of the land in dry regions. Wind Erosion and Deposition
23.4 Glaciers and Wind Abrasion by wind occurs in much the same way as abrasion by flowing water. Wind blows sand against other rocks, slowly sandblasting them away and removing the weathered particles. Wind Erosion and Deposition
23.4 Glaciers and Wind Wind deposits sand in the form of dunes. These large sand dunes are found in the Namib Desert in Africa. Wind Erosion and Deposition
23.4 Glaciers and Wind Effects of Wind Deposition When wind slows down, it drops the sediment it is carrying. Deposits formed from windblown sand are called dunes. Over time, sand dunes can move great distances, as the wind picks up sand from the back of the dune and blows it to the front. Sand dunes can take many different forms, depending on wind direction and how much sand is available. Wind Erosion and Deposition
23.4 Glaciers and Wind Deposits formed from windblown dust are called loess. Loess consists mainly of finely ground particles. The two major sources of loess are deserts and glacial deposits. A dust storm can transport tons of dust for long distances. Dust from the Sahara Desert in Africa regularly blows across the Atlantic Ocean. Wind Erosion and Deposition
23.4 Glaciers and Wind This large dust storm blew through downtown Phoenix, Arizona, in 1999. Wind Erosion and Deposition
23.4 Glaciers and Wind Assessment Questions 1.Large, bowl-shaped valleys carved by glaciers are called a.cirques. b.horns. c.moraines. d.loess.
23.4 Glaciers and Wind Assessment Questions 1.Large, bowl-shaped valleys carved by glaciers are called a.cirques. b.horns. c.moraines. d.loess. ANS:A
23.4 Glaciers and Wind Assessment Questions 2.How does wind erode land? a.plucking and abrasion b.abrasion and slumping c.deflation and abrasion d.deflation and frost wedging
23.4 Glaciers and Wind Assessment Questions 2.How does wind erode land? a.plucking and abrasion b.abrasion and slumping c.deflation and abrasion d.deflation and frost wedging ANS:C