Key Terms: Desert Systems & Processes

Transport Mechanisms: Wind moves sediment through three distinct modes based on particle size. Suspension carries the finest dust high in the air; saltation involves medium-sized grains bouncing along the surface; and surface creep occurs when larger particles roll or slide due to the impact of saltating grains.

Erosional Processes: Deflation is the removal of loose, fine-grained particles by wind, often leaving behind a concentrated layer of larger rocks known as desert pavement. Abrasion is the 'sandblasting' effect where wind-blown grains wear down exposed rock surfaces.

Deposition: Occurs when wind velocity drops below the threshold required to carry a specific grain size. This leads to the formation of Ergs (vast sand seas) or localized dune systems.

Ephemeral vs. Exogenous Rivers: Ephemeral rivers (or wadis) are temporary streams that flow only after heavy rainfall, characterized by high energy and rapid flash flooding. Exogenous rivers (like the Nile) originate in humid regions outside the desert and possess enough volume to survive the high evaporation rates of the arid landscape.

Fluvial Erosion and Deposition: Despite low rainfall, water is a primary sculptor of desert landscapes. Gully erosion carves deep channels during storms, while alluvial plains are formed where sediment-laden water spreads out and loses energy, depositing its load.

Salinisation: High evaporation rates cause dissolved salts to be drawn to the surface through capillary action. As the water evaporates, it leaves behind a toxic, crusty layer of salt that inhibits vegetation and alters soil structure.

Landscape Types: Deserts are categorized by their surface material. An Erg is a sand sea; a Hamada is a high, rocky plateau stripped of sand; and a Reg (or Serir) is a stony plain covered in gravel.

Weathering Mechanisms: Block disintegration occurs when rocks break along joints due to thermal stress, whereas crystal growth (salt weathering) involves the expansion of salt crystals in rock pores, exerting internal pressure that shatters the rock.

Analyze the Budget: When discussing landform change, always reference the sediment budget. If a question asks why a dune is shrinking, explain it in terms of outputs exceeding inputs within that specific sediment cell.

Process-Form Links: Be prepared to link specific processes (like saltation) to specific landforms (like barchan dunes). Always explain the 'how'—for example, how saltation leads to the accumulation of sand on the windward slope.

Avoid the 'Waterless' Myth: A common mistake is assuming water is irrelevant in deserts. In reality, fluvial processes are often the most powerful agents of erosion because desert surfaces lack vegetation to slow down runoff, leading to high-magnitude, low-frequency change.