Test: Biogeography: World Environment - 2 - UPSC MCQ

Seif dunes, or longitudinal dunes, are long narrow ridges of sand lying parallel to the direction of the prevailing winds. These dunes can be over a hundred miles long and are formed by the action of wind on sand particles.

Dunes are hills of sand formed by the accumulation of sand and shaped by the movement of winds. These landforms are a striking characteristic of erg or sandy deserts and can be classified as active or live dunes and inactive or fixed dunes.

Barchan dunes are crescent or moon-shaped live dunes that advance steadily in the particular direction of prevailing winds. They are initiated by a chance accumulation of sand across an obstacle and occur transversely to the wind.

Temporary lakes in arid or semi-arid areas are called Playas, Salina, or Salars. These lakes are formed by intermittent streams flowing into depressions and contain a high percentage of salts due to high evaporation and lower precipitation.

Pediment is an erosional plain formed at the base of the surrounding mountain scarps in desert depressions. It is characterized by steep slopes and is often found alongside Bajada, which is a depositional feature made up of alluvial material.

Abrasion, the sandblasting effect of winds against rock surfaces, is responsible for the formation of rock pillars with mushroom-like shapes. These pillars are known as mushroom rocks or rock pedestals.

Ventifacts are pebbles that are faceted and edged by sandblasting. They are rock fragments weathered from mountains and are shaped and polished thoroughly by wind abrasion.

Yardangs are rock formations that consist of vertical bands of hard and soft rocks aligned in the direction of prevailing winds. Wind abrasion excavates the bands of softer rocks into long, narrow corridors, separating the steep sided overhanding ridges of hard rocks.

Mesas are flat, table-like land masses with a very resistant horizontal top layer and very steep sides. They are formed in canyon regions and may eventually be reduced in area to become isolated flat-topped hills called Buttes.

Loess is a landform characterized by a yellow, friable (softly crumbled) material rich in lime, very coherent, extremely porous, and usually very fertile. It is formed by the deposition of fine dust blown beyond the desert limits onto neighboring lands.