Deserts - Final exam review

Middle-latitude deserts

- Located in the deep interiors of continents - High mountains in the path of the prevailing winds produce a rainshadow desert.

_____is the most effective erosive agent on deserts not_____.

WATER is the most effective erosive agent on deserts not WIND.

Geologic Processes in Arid Climates

Weathering • Not as effective as in humid regions • Mechanical weathering produces unaltered rock and mineral fragments. • Some chemical weathering in deserts produce: - Clay - Thin soils - Oxidized minerals

Basin and Range - Evolution of a Desert Landscape

Characterized by interior drainage • Landscape evolution in the Basin and Range region • Uplift of mountains—block faulting Interior drainage into basins produces: - Alluvial fans - Bajadas - Playas and playa lakes Ongoing erosion of the mountain mass - Produces sediment that fills the basin - Diminishes local relief - Produces isolated erosional remnants called inselbergs

What factor limits the depths of blowouts?

Damp ground and vegetation, this happens when blowouts are lowered to the water table

Distribution and Causes of Dry Lands

Dry regions cover 30% of Earth's land surface. Two climatic types are commonly recognized. 1. Desert or arid 2. Steppe or semiarid Dry lands are concentrated in two regions. 1. Subtropics • Low-latitude deserts • In the vicinities of the Tropics of Cancer and Capricorn • Areas of high pressure and sinking air that is compressed and warmed

Why is rock weathering reduced in deserts?

Lack of moisture and the scarcity of organic acids from decaying plants.

Middle latitude deserts are most common in the ______ hemisphere.

Middle latitude deserts are most common in the NORTHERN hemisphere.

Match dune types:

Parabolic dunes - Dunes whose tips point into the wind Parabolic dunes - Often form along coast where strong winds create a blowout Transverse dunes - Long sand ridges oriented at right angles to the wind Barchan dune - Solitary dunes whose tips point downward Longitude dunes - Long sand ridges that are oriented more or less parallel to the prevailing wind Star dunes - An isolated dune consisting of three or four sharp-crested ridges diverging from a central high point Barchanoid dunes - Scalloped rows of sand oriented at right angles to the wind

Role of water in arid climates

Practically all streambeds are dry most of the time. Desert streams are said to be ephemeral. - Carry water only during periods of rainfall - Different names are used for desert streams in various regions. • Wash and arroyo (western United States) • Wadi (Arabia and North Africa) • Donga (South America) • Nullah (India) Desert rainfall - Rain often occurs as heavy showers. - Because desert vegetative cover is sparse, runoff is largely unhindered and flash floods are common. - Poorly integrated drainage systems and streams lack an extensive system of tributaries. - Most of the erosion work in a desert is done by running water.

What is the most important erosional agent of the desert?

Running water

Wind deposits

Significant depositional landforms are created by wind in some regions. Two types of wind deposits: 1. Dunes • Mounds or ridges of sand • Often asymmetrically shaped • Windward slope is gently inclined and the leeward slope is called the slipface. • Slow migration of dunes in the direction of wind movement • There are several types of sand dunes, including barchan, barchanoid, transverse, longitudinal, parabolic, and star dunes. 2. Loess » Blankets of windblown silt » Two primary sources are deserts and glacial outwash deposits. » Extensive deposits occur in China and the central United States.

Why is the Aral Sea shrinking?

The main reason why the Aral Sea has shrunk so dramatically is because water from the rivers flowing to it has been diverted for irrigation. Human activity has been the main cause Desertification has increased Salinity has increased Dust storms increased Desert which surrounds the Aral has recaimed more and more of the basin.

2 hypotheses used to explain the formation of desert pavement:

The surface is a layer of coarse pebbles and gravels, called desert pavement, too large to be moved by the wind. Deflation removes the finer particles until none available, deflation ends.

Why is wind erosion more important in arid regions?

Transportation and deposition of sediment

Wind in the Desert

Transportation of sediment by wind Differs from that of running water in two ways: 1. Wind is less capable of picking up and transporting coarse materials. 2. Wind is not confined to channels and can spread sediment over large areas. Mechanisms of transport 1. Bed load • Saltation—skipping and bouncing along the surface • About 25% of the sand transported in a sandstorm is moved this way. 2. Suspended load

Wind erosion

Wind is a relatively insignificant erosional agent with most erosion in a desert performed by intermittent running water. Mechanisms of wind erosion 1. Deflation • Lifting of loose material • Deflation produces blowouts (shallow depressions) and desert pavement (a surface of coarse pebbles and cobbles). 2. Abrasion • Produces ventifacts (stones with flat faces) and yardangs (wind sculpted ridges) 3. Limited in vertical extent