Deserts, Glaciers, and Climate

Assignment: Deserts, Glaciers, and Climate

About one-third of the earth's landmass is desert or semi-desert. These regions have unique geologic features not found in more humid environments. These features are most often caused by wind and water erosion in the stark desert environment. Desserts are usually created because they are located in a Rain Shadow which is a dry region downwind of mountain ranges caused by air losing its moisture as it passes over mountains.

Desert areas usually have Internal Drainage. When streams drain toward landlocked basins rather than flowing eventually to the sea. When the water from these basins dries it is called a playa. Because of the factors above, deserts often have less vegetation to prevent erosion, which in turn leads to further barrenness through Deflation -- the removal of silt and sand particles from the land surface by wind.

Below are some geologic features and unique characteristics of the desert regions: Alluvial Fan, a large, fan-shaped pile of sediment -- unconsolidated gravel, sand, silt and clay -- forming at the base of narrow canyons onto a flat plain at the foot of a mountain range. Arroyo is a dry desert gully, usually a small, narrow canyon with steep walls and flat, gravel strewn floor. Bajada, a broad, sloping depositional surface at the base of a mountain range caused by the coalescing of alluvial fans. Blowout is a depression in the land surface caused by wind erosion. Butte, a narrow, flat-topped hill of resistant rock with very steep sides. Probably formerly a mesa. Desert Pavement, a thin, surface layer of closely packed pebbles. Desert Varnish is a hard, dark, shiny coating on rocks caused by chemical/biological action. Dunes are mounds of loose sand grains shaped by the wind.

Flash Flood is a sudden local flood of high discharge and short duration. Hoodoo, a bizarre-shaped column or pillar caused by differential erosion on rocks of different hardness. Loess is deposit of wind-blow silt and clay...