Geo Chapter 15

(A)eolian

“work of wind”

Eolian erosion

Removal of material in a landscape by wind. Controlled by the overall size of the particle or grain.

Intermediate particles

Move easily by bouncing

Large particles

Resist movement due to their weight

Small particles

Resist movement due to their mutual cohesiveness

Deflation

Eolian erosion from the lifting and removal of individual loose particles. Desert pavements prevent further deflation.

Abrasion

Eolian erosion from the grinding of rock surfaces with a “sandblasting” action

Desert pavement

An area dominated by pebbles and rocks due to the removal of fine sediments by wind and water, or the deposition of fine sediments and upward deposit of gravels due to cycles of swelling and shrinking. Disturbance may lead to further deflation

Blowout depression

Basins created by the removal of material, from 1-100+ meters in size.

Abrasion landforms

Vary by hardness of rock surfaces, wind velocity, and wind consistency. Limited to 1-2 meters above ground

Ventifact

A rock shaped by the abrasive force of wind-blown particles. Often pitted, polished or aerodynamically shaped.

Yardang

An elongated wind-sculpted ridge

Alveoli

Small pits in the surface of a rock, such as sandstone, caused by eolian abrasion.

Eolian transportation

The drag or frictional pull exerted on particles until they become airborne. Distance carried depends on particle size and wind speed.

Suspension

Particles carried in the turbulent flow of the air.

Saltation

Particles carried by the wind by bouncing along the surface.

Surface creep

The sliding or rolling of particles across the ground due to the impact of saltation.

Amount of deserts covered in sand

10%

Ripples

Small features of linear crests and troughs formed transversely (at right angles) to wind. An olian depositional landform.

Dune

Transient. wind sculpted ridges or hills composed of sand. An eolian depositional landform.

Erg

A sand sea or an area predominated by dunes. An eolian depositional landform.

Stoss slope

The upward, gentler slope of a dune.

Slipface

The “edge” of a dune

Leeward slope

The steeper, downward slope of a dune.

Angle of repose

The steepest angle at which particles are stable.

Barchan dunes

Crescent-shaped dunes with “horns” that point
downwind. Found in areas with consistent winds and little
directional variability, and where the sand supply is limited.

Parabolic dunes

Similar to barchan dunes, but facing upwind rather than downwind. May have vegetation on either side. Appear in areas with slightly more water/vegetation and with lower sand supply.

Transverse dunes

A long, slightly sinuous dune with an asymmetrical
ridge, and only slip face on the backside. Aligned transverse or perpendicular to the wind direction. Appear in areas where wind is typically weak.

Barchanoid ridges.

Wavy, asymmetrical dunes that form where coalescence of barchen dunes begins. Aligned transverse to the wind direction.

Longitudinal dunes

Linear, sinuous ridges that are aligned parallel with the wind direction. Average about 100 meters high and 100 kilometers long, but can reach even higher elevations.

Star dunes

A pyramid-shaped dune with three or more sinuous ridges radiating out from it. Occur where there's a lot of sand supply and a consistently changing wind direction.

Reversing dunes

A dune with an asymmetrical ridge. Intermediate between a star dune and a transverse dune.

Loess Deposits

Thick deposits of fine-grained clays and silts accumulated in various parts of the world by eolian processes. Considered fertile soils because they are thick, well drained, and capable of retaining moisture.

Dry climate prevalence

About 26% of Earth’s surface (more when considering semi-arid climates).

Climate controls of deserts

Subtropical highs (15-15 degrees N/S), rain shadows of mountains, and continentality.

Desert characteristics

High sensible heat, high ground heating, high POTET and large DEFIC of precipitation, intermittent streams

Flash flood

A sudden torrent of water that fills a channel. Common desert fluvial landform.

Wash (arroyo)

A dry stream bed

Playa

A temporary lake, existing only during wet periods, especially in deserts

Exotic streams

A stream whose headwaters originate in a different type of climate.

Alluvial fan

A fan-like deposit of sediments at the mouth of a canyon stream

Bajada

A broad slope composed of several alluvial fans.

Cross-bedding

Any time where the alignment of material in a layer of rock is at a different angle than an adjacent layer of rock material.

Basin and Range Province

An arid desert province in the Southwest US and parts of Mexico. Part of an area of internal drainage, predominant tectonic structure of normal faulting. Evaporative in their potential, leaving salt flats and salt deposits across the valley floor bottoms.

Desert varnish

Thin. dark coating composed of clay particles, iron and manganese caused by weathering and biologic action. Important for petroglyphs and cultural/historical dating.

Cliff dwellings

Habitations built in the alcoves formed commonly in sandstone by frost wedging and salt crystal growth.

Mesa

A flat-topped landform with steep sides and elevated from surroundings.

Butte

Smaller, steep-sided landform formed from weathering of mesas.

Inselburgs

Isolated remnants formed from resistant rock.

Desertification

The process of degradation of dryland ecosystems, resulting in the loss of biologic or human usefulness. A worldwide landscape degradation phenomena.

Human-driven processes of desertification

Overgrazing, abuse of soil structure (compaction.over tilling), chemical changes (soil salinization), over-watering (elevated water table), nutrient depletion, deforestation, climate change