Module 8 Eolian Systems

rain shadow deserts

A third place where eolian landscapes are found is the rain shadow deserts of the world. These are located behind mountain ranges. The mountains intercept warm moist air, so that the backside of the mountain is dominated by dry and cool air that descends down the mountain and makes the other side a desertEolian landforms are common in deserts, where vegetation is sparse.

Weathering is a necessary first step before eolian landscapes can form. Why?

Before wind can erode away soil and sand particles, weathering has to first create those particles. Small unconsolidated particles are produced by weathering. They are then further eroded away by the wind.

deflation basin

Deflation basins are left behind after the wind removes the surface sediment

desert pavement

Desert pavement is made of lag deposits that harden together over time

subtropical desert

Eolian landscapes are most common in the subtropical desert areas of the world; those parts of the world where vegetation is sparse and there is an abundant supply of loose, unconsolidated sediment. In these subtropical regions, dry descending air makes for dry deserts on the ground. The low moisture level means that the soil is easily blown away by wind.

Eolian landforms are also common in dry areas with very little humidity. How does the air's moisture level affect wind erosion?

Humid climates discourage wind erosion. High humidity means more rainfall, more vegetation, and more moist soil. Moist, vegetated soil is much harder for wind to erode away than dry, bare soil. Water holds soil particles together and gives them greater cohesion.

ventifacts

Pebbles that are shaped and polished by the wind are called ventifacts.

rain shadow desert

Rain shadow deserts form on the back sides of mountains.

sand dunes

Sand dunes need three things to form: -an adequate supply of loose sand -wind to blow the sand -something that causes the sand to settle like a rock or clump of grass

cross beds

The bands are cross-beds. They represent different stages of sand deposition in a sand dune.

lag deposists

The large deposits left behind are the lag deposits. Wind usually removes only sand and dust-sized particles. Larger sediment is left behind; this is called the lag deposit. Lag deposits harden together to form desert pavement, like you see in this image. Desert pavement acts like a protective covering that keeps the soil from further deflation

Eolian landforms are common in deserts, where vegetation is sparse. What effect does vegetation have on the wind's ability to shape the landscape?

Vegetation holds the soil down, acting like an anchor that keeps it from blowing away in the wind. If there is no vegetation at all, such as in extreme desert environments, the soil easily blows away

coastal environments

While eolian landscapes are most common in the subtropical deserts, they are also found in coastal environments, where winds are high and there is an abundant supply of loose sand on the ground.

loess

Wind not only deposits sand in sand dunes; it also deposits accumulations of silt and clay (dust). Loess blankets many regions throughout the world. It is composed mostly of silt-sized grains, but clay particles may also be present. Loess deposits are commonly found away from deserts, because the loess is blown away from them.

yardangs

Yardangs are long linear ridges shaped by abrasive wind erosion.

eolian systems

environments shaped by wind. Because they are driven by wind, eolian systems derive all their energy from the Sun—since incoming solar radiation affects all of Earth's winds.

abrasion

or the sandblasting action of wind-blown sand. Both sediment removal and abrasion work to erode eolian environments. Sandblasting. Wind abrasion is like sandblasting. Wind-blown grains of sand impact rock surfaces and small particles are knocked off the rock. Pebbles that have been shaped and polished by the wind are called ventifacts. The abrasive action of sand can also leave grooves and polished surfaces on desert pavement. Though less common, wind abrasion does produce larger landforms in some desert regions linear ridges, called yardangs. Yardangs, like the ones shown here, resemble the hull of a boat. Facing the wind is a steep blunt face that gradually gets lower and narrower through abrasive erosion. Yardangs form only in the driest areas of deserts.

deflation

the removal of loose particles of sand from a particular area. It is the most significant type of wind erosion. It occurs only where loose material is exposed at the surface. The feature left behind after the removal of sand is called a deflation basin. These landscape features can cover several hundred kilometers in area and are associated with many of the world's deserts.