GEOL 1340 Unit 10 Deserts and Wind Deposits

What defines a desert?

Aridity (low precipitation), not temperature.

Are all deserts hot?

No, deserts can be extremely cold, such as polar deserts.

Subtropical Deserts Example & Characteristics

Sahara, Arabian, and Kalahari; characterized by high temperatures, very low precipitation, and warm soils.

Rain-Shadow Deserts Example & Mechanism

Eastern Oregon; formed when major mountain ranges block moisture-bearing winds, creating dry conditions on the leeward side.

Coastal Deserts Example & Mechanism

Atacama and Namib; located along western continental margins where cold ocean currents cool the overlying air, inhibiting moisture retention.

Continental Interiors Example & Characteristics

Gobi; located deep within large landmasses far from moisture sources, experiencing hot summers and cold winters.

Polar Deserts Characteristics

Antarctica; mean temperature below 10 degrees Celsius during the warmest month and annual precipitation no more than 250 mm.

Primary Weathering Type in Deserts

Physical weathering dominates because chemical weathering requires abundant moisture.

Calcrete Definition

A hard layer formed in desert soils when percolating dissolved ions precipitate calcite.

Role of Water in Deserts

Although rain is rare, water is the dominant force shaping desert landscapes.

Ephemeral Streams Definition

Streams that flow only immediately following a rare rain event, causing quick flash flood erosion.

Surface Load Composition

Coarser sand-sized grains moved via saltation and surface creep.

Suspended Load Composition

Finer dust and silt-sized particles lifted high into the atmosphere to travel long distances.

Deflation Definition

The lowering of the desert land surface caused by wind removing loose, fine-grained sediment to create blowouts.

Lag Deposits & Desert Pavement

An erosion-resistant surface layer of coarse stones left behind when wind blows away all finer sediment.

Ventifacts Definition

Stones that have been sandblasted, faceted, and polished by windblown sand.

Yardangs Definition

Large, streamlined, wind-sculpted bedrock knobs.

Talus Aprons Location & Shape

Accumulations of angular rock debris resting at the angle of repose at the base of cliffs, shaped by jointing.

Alluvial Fans Formation

Conical accumulations of sediment formed where water exiting a steep canyon spreads out and drops its sediment load.

Playas Definition

Flat-bottomed desert lakes with no outlet streams that periodically dry up, leaving behind thick salt crystal crusts.

Loess Definition

Thick blankets of windblown silt (dust) deposited downwind of deserts.

Barchan Dunes

Crescent-shaped dunes that form when sand is scarce and winds blow steadily in one direction.

Star Dunes

Pyramidal dunes with multiple ridges that form when sand is scarce and winds shift directions frequently.

Transverse Dunes

Long ridges perpendicular to moderate winds that form when there is enough sand to cover the ground.

Parabolic Dunes

U-shaped dunes with tips pointing upwind that form when strong winds breach transverse dunes and vegetation anchors the sides.

Longitudinal Dunes

Long, linear ridges parallel to strong, steady winds with abundant sand supply.

Desertification Definition

The conversion and aridification of productive, non-desert land into desert conditions due to a combination of climate change and human activities.

Role of Farming & Human Activities in Desertification

Overgrazing, unscientific land-use changes, and poor agricultural practices strip away protective vegetative cover and expose soil to severe erosion.

Aral Sea Case Study

The dramatic shrinkage of the Aral Sea due to water diversion for agriculture illustrates how human intervention triggers regional desertification.

Consequences of Desertification

Biodiversity loss, food insecurity, increased human-wildlife conflicts, and massive dust storms carrying hazardous chemicals and pathogens.

Prevention and Restoration Strategies

Protecting vegetative cover, sustainable land and water management, integrating grazing with farming, soil enrichment, planting trees, and establishing seed banks.