What are the characteristics found in arid environments that contribute to the formation of unique desert landscapes?

Answer 1

In dry regions, mechanical weathering is more prominent and processes such as salt wedging are more common than those that require an abundance of water. In arid regions, the bedrock is exposed to more erosive forces since there is very little soil covering it. The bedrock allows little water to permeate so there is substantial runoff when it rains.

Another well-known aspect of deserts is the relative abundance of sand. In these sand covered regions, the water sinks into the ground and inhibits overland flow. Erosion occurs with storms where there are heavy rains that can move the sand and create wind-blown sand formations. However, rainfall in arid areas is usually intense, but short-lived. Floods and flash flooding are common. Because of the lack of moisture, most streams are ephemeral and the debris from flooding creates a mantle of alluvium.

Desert vegetation is sparse and spiny due to the lack of rainfall. Most vegetation consists of widely-spaced shrubs and grasses. Additionally, there is little surface water in desert regions. Most streams that flow through arid regions are exotic streams. The water that feeds these streams comes from an adjacent humid region or higher elevation. These streams diminish downstream as the water seeps into the ground, evaporates or is tapped for irrigation of adjacent farmlands.

Permanent lakes are uncommon in arid regions. Occasionally, the dry lakebed can fill up because of rainfall and then it becomes a temporary playa lake. Many permanent lakes in desert regions are saline lakes. The high evaporation leads to the accumulation of dissolved salts in the soil.

Differential erosion is more prominent in the desert. Differences in rock hardness produce resistance to erosion in some areas and the abundance of erosion in adjacent structures. Steep rock faces are evidence of differential erosion.

A depositional feature found in arid lands is a piedmont. A piedmont is a zone at the foot of a mountain range and is an area of fluvial deposition. The change in slope from the steep mountainside to the piedmont results in slowing of streams flowing down the mountain slope. The slower stream flow allows more materials to deposit in this zone.

Landscape surfaces distinctive to desert areas include ergs, regs, and the hamada. Ergs are large areas covered with loose sand usually with numerous dune formations. Regs are stony desert coverings often referred to as desert pavement. The loose material has been blown away by the wind, leaving pebbles that fit together and seal off lower levels from erosion. The hamada is a barren surface of exposed bedrock with little loose material on the surface.

Desert varnish is a dark, shiny coating composed mostly of iron and manganese oxides. The varnish is a consequence of biochemical processes and important to dating rocks since the longer the surface is exposed, the darker the color and the older the rocky surface.

Wind is an important erosional and depositional process in the desert and is called an aeolian process. The effects in aeolian processes are either deflation or abrasion. Deflation occurs when loose particles are shifted along the ground or in the air. No significant features are created by deflation.

Abrasion occurs when windblown particles shape an existing landform. The result is pitting, etching, or polishing of the surface. Rocks that are sandblasted and shaped by this process are known as ventifacts. Wind carries particles of sand and dust differently based on their size. The finest, lightest particles are suspended above the surface. Saltation is a term that refers to the movement of particles above the surface in a lower, curved arc. Traction moves larger particles, too heavy for saltation, by pushing them along the ground.