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Deserts. Intro Deserts cover 25 % of Earth’s land surface 13 % of population live on deserts We have adapted irrigations systems to water crops.

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Presentation on theme: "Deserts. Intro Deserts cover 25 % of Earth’s land surface 13 % of population live on deserts We have adapted irrigations systems to water crops."— Presentation transcript:

1 Deserts

2 Intro Deserts cover 25 % of Earth’s land surface 13 % of population live on deserts We have adapted irrigations systems to water crops

3 Why deserts Exists the equator – The air absorbs moisture equatorial oceans and rises because it is warmer and therefore is less dense, than the surrounding air. Rising air cools as pressure decreases. But cool air cannot hold as much water as warm air so the water vapor condenses and falls as rain. This equatorial air is drier because loos of moisture and flows northward and southward at high altitudes

4 Desserts

5 Mountains: Rain-Shadow Mountains

6 Desert lakes and Desert Streams

7 Pediments and Bajadas Pediment is a broad, gently sloping surface eroded into bedrock. The bedrock surface of a pediment is covered with a thin veneer of gravel that is on the process of being transported from the mountain across the mountain to the bajada

8 The Colorado Plateau and Great Basin

9 Wind Wind Erosion Wind erosion is called deflation is a selective process. Air is much less then water, wind

10 Transport and Abrasion To move sand-sized particles, wind first pushes them along the surface. If the particle is too heavy to be lifted, it continues to move forward along the ground in a movement called creep. Smaller or lighter sediments are picked up into the wind flow when the speed (or velocity) of the wind flow is great enough to lift them up. But even after they're lifted, the particles are still subjected to the pull of gravity, so after a short period of suspension they fall back to the surface. This type of particle motion is called saltation: The particle jumps along the surface, being repeatedly lifted and dropped as it moves in response to the force of the wind flow. As the particles land, they bounce farther along and bump other which may begin to sulfate or move forward in the same manner In this way the bed load of a wind current is filled with sand-sized sediment bouncing along in the direction of the wind flow. If the surface is very hard, the bed load may extend up to 2 meters (about 6.S feet) above the surface because objects bounce higher off a more compact surface. For example, a marble onto grass, it will not bounce or move very far. But if you same marble onto pavement, it will bounce and move much farther

11 Dune Is a mound or ridge of wind –deposited sand Heights  30 to 100 m Some exceed 500 m

12 Creation bedding  Cross beds

13 Types of Sand Dunes

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16 Loess

17 Desertification

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