Definition: Deserts are continental environments characterized by low precipitation. Often, they are seasonally hot, but not always. Their general characteristics:

Major transport media:

Being dry, deserts are places where day by day, the wind tends to overshadow water as the dominant transport medium. Water is still the overall dominant medium, but it is sporadic. We will therefore discuss wind and water driven erosion, transport, and deposition separately.

Eolian erosion, transport, and deposition: The term eolian refers to the wind-dominated geological processes.

Big Concept: Air, like water is a fluid so, like water, it transports materials as bed load and suspended load. Air is much less viscous and dense; however, so only silt and clay sized particles can be carried as suspended load. The rest is bed load.

Bed load transport:

Suspended load: Silt & clay sized particles resist being taken into suspension, but once they are up, they tend to remain suspended for long periods.

Eolian erosion.

Surface textures caused by eolian erosion:

Eolian deposition: Think "sand dunes." Eolian dunes are like subaqueous dunes, only different. Any topographic irregularity can create a wind shadow in which sand will be deposited, adding to the irregularity and provoking more deposition. Presto a dune is born.

Dune morphology: A typical eolian dune forms from the deposition of saltating sand grains. Typically a dune is an ephemeral structure that migrates, divides or fuses with other dunes. It displays:

Conditions for dune formation: Most deserts are rocky, so dunes are actually rare. 10% of Sahara, tiny % of SW US. Still, in some places large amounts of sand accumulate in sand seas called ergs. Examples occur in Sahara and Empty quarter of the Arabian Penninsula. What governs the location, size, and shape of dune formation?

Depending on how these factors covary we can get four basic dune types.

Dunes in the rock record: So what happens if the water table rises beneath a dune field? The dunes can be immobilized and, eventually lithified by the precipitation of cements. The result is an eolian sandstone.
The suspended load: Loess [German - "yellowish gray soil"]: This consists of deposits of wind blown silt and clay.

Water dominated deposition in deserts:



Key concepts and vocabulary: