2. Surface Water, Wind, Ice, and Land Movement

3. Stream Bed A stream’s bed is the bottom, or rock and soil not moving with the water. Surface Water Movement A stream is a moving body of water.

4. A stream load includes the living components of water, such as animals and plants, and the nonliving components, including sediments and dissolved gases. A stream carries its load in solution, suspension, or as bed load. Stream Load A stream’s load includes all the materials that the water in a stream carries. Surface Water Movement

5. A bed load includes the heavy materials that roll slowly along the bottom. Bed Load Surface Water Movement

6. Stream Load Suspension Surface Water Movement –All particles small enough to be held in the water by the turbulence of a stream’s moving water are carried in suspension. –Particles, such as silt, clay, and sand, are part of a stream’s suspended load. –The higher the volume and velocity, the more particles in suspension

7. A stream’s water moves more quickly where there is less friction and greater slope and can carry more material. The total volume of moving water also affects a stream’s carrying capacity. A stream’s carrying capacity is its ability to transport material. Surface Water Movement

8. Stream Velocity and Carrying Capacity Surface Water Movement Which area will have the greatest carrying capacity? Which area will have the least carrying capacity?

9. Floodplains develop highly fertile soils as more sediment is deposited with each subsequent flood. Floodplains-flat low land next to rivers After flooding, the floodwater recedes and its volume and speed decrease, the water drops its sediment load onto the stream’s floodplain. Surface Water Movement

10. Moving Water Carves a Path Stream banks, the ground bordering the stream on each side, hold the moving water within the confines of the stream channel. Stream Development Headward erosion is the process by which small streams erode away the rock or soil at the head of the stream.

11. Formation of Stream Valleys As a stream actively erodes its path through the sediment or rock, a V-shaped channel develops. Young Stream! Stream Development A stream continues to erode until it reaches its base level, the elevation at which it enters another stream or body of water. Over time, a V-shaped valley will be eroded into a broader valley that has gentle slopes. Old Stream

12. Meandering Streams A stream’s slope, or gradient, decreases as it nears its base level, and as a result the channel gets wider causing water to build up within the stream channel. Stream Development Sometimes, the water begins to erode the sides of the channel and the stream starts to bend or wind. A meander is a bend or curve in a stream channel caused by moving water.

13. Meandering Streams Water in the straight parts of a stream flows at different velocities, depending on the location of the water in the channel. Stream Development –In a straight length of a stream, water in the center of the channel is flowing at the maximum velocity. –Water along the bottom and sides of the channel flows more slowly because it experiences friction as it moves against the land.

14. Meandering Streams The water moving along the outside of a meander curve experiences the greatest rate of flow within the meander. Stream Development –The water that flows along this outside part of the curve continues to erode away the sides of the streambed, thus making the meander larger. –Along the inside of the meander, the water moves more slowly and deposition is dominant.

15. Meandering Streams

16. It is common for a stream to cut off a meander and once again flow along a straighter path. Stream Development The cut off meander becomes an oxbow lake, which eventually dries up. As a stream approaches its ultimate end point, the ocean, the streambed’s gradient flattens out and its channel becomes very wide. The mouth is the area of the stream that leads into the ocean or another large body of water.

17. Erosion is the removal and transport of weathered material from one location to another. Weathering is the chemical and physical processes by which rocks on or near Earth’s surface break down and change. Weathering Changes occur every day to Earth’s rocks and surface features. Weathering

18. Mechanical Weathering Mechanical and chemical weathering are the two processes that can wear down rocks and minerals. Weathering Both types of weathering occur at the same time on Earth’s landforms. Mechanical weathering, or physical weathering, is the process by which rocks and minerals break down into smaller pieces without changing their composition. Mechanical weathering does not involve any change in a rock’s composition.

19. Chemical Weathering Chemical weathering is the process by which rocks and minerals undergo changes in their composition as the result of chemical reactions. Weathering Significant agents of chemical weathering include water, oxygen, carbon dioxide, and acids. Chemical reactions between rocks and water result in the formation of new minerals and the release of dissolved substances. Some minerals, such as calcite, may dissolve completely.

20. Deposition of Sediments A stream’s velocity lessens and its sediment load drops when its gradient abruptly decreases. Stream Development In dry regions, a stream’s gradient may suddenly decrease causing the stream to drop its sediment as a fan-shaped deposit called an alluvial fan. Alluvial fans are sloping depositional features formed at the bases of slopes and composed mostly of sand and gravel.

21. Alluvial Fans- a river does not run through it!

22. Deposition of Sediments Streams also lose velocity and the ability to carry sediment when they join larger bodies of quiet water. Stream Development A delta is the triangular deposit, usually consisting of silt and clay particles, that forms where a stream enters a large body of water.

23. River Deltas -soil deposits from continual water flow into a larger body of water

24. Wind Moving air can pick up and transport Earth materials in the process of erosion. Wind Unlike water, wind can transport sediments uphill as well as downhill. As an erosional agent, wind can change landscapes in arid and coastal areas with little vegetative cover

25. Wind Deposition Formation of Dunes Wind –In wind-blown environments, sand particles tend to accumulate where an object blocks the particles’ forward movement. –A dune is a pile of wind-blown sand that develops over time. –Conditions, including the availability of sand, wind velocity, wind direction, and the amount of vegetation present under which a dune forms, determine its particular shape.

26. Wind Deposition-dune formation

27. Moving Masses of Ice A glacier is a large, moving mass of ice. Glaciers Glaciers form near Earth’s poles and at high elevations and cover only about 10 percent of Earth’s surface. Cold temperatures year-round keep fallen snow from melting. It accumulates in an area called a snowfield. The weight of the top layers exerts downward pressure that forces the snow below to recrystallize into ice.

28. Moving Masses of Ice Valley Glaciers Glaciers –Glaciers can be classified as one of two types: valley glaciers or continental glaciers. –Valley glaciers are glaciers that form in valleys in high, mountainous areas. –As valley glaciers flow downslope, their powerful carving action widens V-shaped stream valleys into U-shaped glacial valleys.

29. Erosional Features from Glaciers

30. Moving Masses of Ice Continental Glaciers Glaciers –Continental glaciers, also called ice sheets, are glaciers that cover broad, continent-sized areas. –A continental glacier is thickest at its center. –The weight of this thicker central region forces the rest of the glacier to flatten out in all directions. –Continental glaciers are confined to Greenland, northern Canada, and Antarctica.

31. Variables That Influence Mass Movements Some common types of mass movement include: Mass Movements at Earth’s Surface

32. Types of Mass Movements Creep Mass Movements at Earth’s Surface –Creep is the slow, steady, downhill flow of loose, weathered Earth materials, especially soils. –The effects of creep usually are noticeable only over long periods of time. –Loose materials on almost all slopes undergo creep. –Soil creep moves huge amounts of surface material each year.

33. Types of Mass Movements Flows Mass Movements at Earth’s Surface –In some mass movements, Earth materials flow as if they were a thick liquid. –Mudflows are swiftly moving mixtures of mud and water. –Mudflows can be triggered by earthquakes or similar vibrations and are common in volcanic regions. –Mudflows are also common in sloped, semi- arid regions that experience intense, short- lived rainstorms.

34. Types of Mass Movements Slides Mass Movements at Earth’s Surface –A landslide is a rapid, downslope movement of Earth materials that occurs when a relatively thin block of loose soil, rock, and debris separates from the underlying bedrock. –The material rapidly slides downslope as one block, with little internal mixing. –A rock slide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface

35. Types of Mass Movements Slumps Mass Movements at Earth’s Surface –A slump results when the mass of material in a landslide rotates and slides along a curved surface. –Slumps may occur in areas that have thick soils on moderate-to-steep slopes. –Slumps are common after rains and leave crescent-shaped scars on slopes.

36. Types of Mass Movements Avalanches Mass Movements at Earth’s Surface –Avalanches are landslides that occur in mountainous areas, usually on steep slopes of at least 35°, with thick accumulations of snow. –Avalanches usually occur when snow has melted, and then refrozen into an icy layer. –Snow that falls on top of this crust can eventually build up, become heavy, slip off, and slide down a slope as an avalanche. –A vibrating trigger, even from a single skier, can send such an unstable layer sliding down a mountainside.