13 Deserts

Learning Objectives

By the end of this chapter, students should be able to:

  • Explain the defining characteristic of a desert and distinguish between the three broad categories of deserts.
  • Explain how geographic features, , atmospheric circulation, and Coriolis Effect influence where deserts are located.
  • List the primary desert and processes.
  • Identify desert landforms.
  • Explain how desert landforms are formed by and .
  • Describe the main types of sand and the conditions that form them.
  • Identify the main features of the desert (United States).
The hot deserts are all near 30 north or south latitude.
Figure 13.1: World hot deserts (BWh indicated in red).

Approximately 30% of the Earth’s surface consists of deserts, which are defined as locations of low . While extremes are often associated with deserts, they do not define them. Deserts exhibit extreme temperatures because of the lack of moisture in the , including low humidity and scarce cloud cover. Without cloud cover, the Earth’s surface absorbs more of the Sun’s energy during the day and emits more heat at night.

There is a dry and wet side to the mountain due to air movement.
Figure 13.2: Mountainous areas in front of the prevailing winds create a rain shadow.

Deserts are not randomly located on the Earth’s surface. Many deserts are located at latitudes between 15° and 30° in both hemispheres and at both the North and South Poles, created by prevailing wind circulation in the . Sinking, dry air currents occurring at 30° north and south of the equator produce that create deserts like the African Sahara and Australian Outback.

There are several ranges, some more snowy than others.
Figure 13.3: In this image from the ISS, the Sierra Nevada Mountains are perpendicular to prevailing westerly winds, creating a rain shadow to the east (down in the image). Note the dramatic decrease in snow on the Inyo Mountains.

Another type of desert is found in the rain shadow created from prevailing winds blowing over mountain ranges. As the wind drives air up and over mountains, atmospheric moisture is released as snow or rain. Atmospheric pressure is lower at higher elevations, causing the moisture-laden air to cool. Cool air holds less moisture than hot air, and occurs as the wind rises up the mountain. After releasing its moisture on the windward side of the mountains, the dry air descends on the leeward or downwind side of the mountains to create an arid region with little called a rain shadow. Examples of rain-shadow deserts include the Western Interior Desert of North America and of Chile, which is the Earth’s driest, warm desert.

Finally, , such as vast areas of the Antarctic and Arctic, are created from sinking cold air that is too cold to hold much moisture. Although they are covered with ice and snow, these deserts have very low average annual . As a result, Antarctica is Earth’s driest .


Video 13.1: Rain shadow.

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13.1 The Origin of Deserts

13.1.1 Atmospheric Circulation

Geographic location, atmospheric circulation, and the Earth’s rotation are the primary causal factors of deserts. Solar energy converted to heat is the engine that drives the circulation of air in the and water in the oceans. The strength of the circulation is determined by how much energy is absorbed by the Earth’s surface, which in turn is dependent on the average position of the Sun relative to the Earth. In other words, the Earth is heated unevenly depending on and . is a line circling the Earth parallel to the equator and is measured in degrees. The equator is 0° and the North and South Poles are 90° N and 90° S respectively (see the diagram of generalized atmospheric circulation on Earth). is the angle made by a ray of sunlight shining on the Earth’s surface. Tropical zones are located near the equator, where the and are close to 0°, and receive high amounts of solar energy. The poles, which have latitudes and angles of incidence approaching 90°, receive little or almost no energy.

An illustration of the earth with three generalized circulation cells shown for each hemisphere.
Figure 13.4: Generalized atmospheric circulation.

The figure shows the generalized air circulation within the . Three cells of circulating air span the space between the equator and poles in both hemispheres, the , the Ferrel or Midlatitude Cell, and the . In the located over the tropics and closest to the equatorial belt, the sun heats the air and causes it to rise. The rising air cools and releases its contained moisture as tropical rain. The rising dried air spreads away from the equator and toward the north and south poles, where it collides with dry air in the Ferrel Cell. The combined dry air sinks back to the Earth at 30° . This sinking drier air creates belts of predominantly high pressure at approximately 30° north and south of the equator, called the horse latitudes. Arid zones between 15o and 30o north and south of the equator thus exist within which desert conditions predominate. The descending air flowing north and south in the Hadley and Ferrel cells also creates prevailing winds called near the equator, and in the temperate zone. Note the arrows indicating general directions of winds in these zones.

The area covers most of Nevada, easternmost California, southern Idaho, and western Utah.
Figure 13.5: USGS Map of the Great Basin Desert.

Other deserts, like the that covers parts of Utah and Nevada, owe at least part of their origin to other atmospheric phenomena. The , while somewhat affected by sinking air effects from global circulation, is a rain-shadow desert. As westerly moist air from the Pacific rises over the Sierra Nevada and other mountains, it cools and loses moisture as condensation and on the upwind or rainy side of the mountains.

It is in west-central South America
Figure 13.6: Map of the Atacama desert (yellow) and surrounding related climate areas (orange).

One of the driest places on Earth is the of northern Chile. The occupies a strip of land along Chile’s just north of 30°S, at the southern edge of the trade-wind belt. The desert lies west of the Andes Mountains, in the rain shadow created by prevailing blowing west. As this warm moist air crossing the Amazon meets the eastern edge of the mountains, it rises, cools, and precipitates much of its water out as rain. Once over the mountains, the cool, dry air descends onto the . Onshore winds from the Pacific are cooled by the Peru (Humboldt) ocean current. This super-cooled air holds almost no moisture and, with these three factors, some locations in the have received no measured for several years. This desert is the driest, non-polar location on Earth.

The sinking air is centered just north of Greenland, close to the north pole.
Figure 13.7: The polar vortex of mid-November, 2013. This cold, descending air (shown in purple) is characteristic of polar circulation.

Notice in the figure that the polar regions are also areas of predominantly high pressure created by descending cold dry air, the . As with the other cells, cold air, which holds much less moisture than warm air, descends to create . This is why historically, land near the north and south poles has always been so dry.

13.1.2 Coriolis Effect

Animation illustrating a ball thrown on a rotating disc. Viewed from the perspective of a stationary viewer on the disc, it appears to follow a curved path.
Figure 13.8: In the inertial frame of reference of the top picture, the ball moves in a straight line. The observer, represented as a red dot, standing in the rotating frame of reference sees the ball following a curved path. This perceived curvature is due to the Coriolis Effect and centrifugal forces.

The Earth rotates toward the east where the sun rises. Think of spinning a weight on a string around your head. The speed of the weight depends on the length of the string. The speed of an object on the rotating Earth depends on its horizontal distance from the Earth’s of rotation. Higher latitudes are a smaller distance from the Earth’s rotational , and therefore do not travel as fast eastward as lower that are closer to the equator. When a fluid like air or water moves from a lower to a higher , the fluid maintains its momentum from moving at a higher speed, so it will travel relatively faster eastward than the Earth beneath at the higher latitudes. This factor causes deflection of movements that occur in north-south directions.

Effect of gravity and the centripetal force to produce the Coriolis Effect on an E-W moving mass on the rotating Earth
Figure 13.9: Forces acting on a mass moving East–West on the rotating Earth that produce the Coriolis Effect.

Another factor in the Coriolis effect also causes deflection of east-west movement due to the angle between the centripetal effect of Earth’s spin and gravity pulling toward the earth’s center (see figure 13.9). This produces a net deflection toward the equator. The total Coriolis deflection on a mass moving in any direction on the rotating Earth results from a combination of these two factors.

Since each hemisphere has three atmospheric cells moving respectively north and south relative to the Earth beneath them, the Coriolis effect deflects these moving air masses to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The Coriolis effect also deflects moving masses of water in the ocean currents.

For example, in the northern hemisphere , the lower altitude air currents are flowing south towards the equator. These are deflected to the right (or west) by the Coriolis effect. This deflected air generates the prevailing that European sailors used to cross the Atlantic Ocean and reach South America and the Caribbean Islands in their tall ships. This air movement is mirrored in the in the southern hemisphere; the lower altitude air current flowing equatorward is deflected to the left, creating that blow to the northwest.

Illustration of the Earth with circles showing the Coriolis deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Figure 13.10: Inertia of air masses caused by the Coriolis Effect in the absence of other forces.

In the northern Mid-Latitude or Ferrel Cell, surface air currents flow from the horse latitudes ( 30°) toward the North Pole, and the Coriolis effect deflects them toward the east, or to the right, producing the zone of westerly winds. In the southern hemisphere Mid-Latitude or Ferrel Cell, the poleward flowing surface air is deflected to the left and flows southeast creating the Southern Hemisphere .

Another Coriolis-generated deflection produces the . At 60o north and south , relatively warmer rising air flows poleward cooling and converging at the poles where it sinks in the polar high. This sinking dry air creates the , the driest deserts on Earth. Persistence of ice and snow is a result of cold temperatures at these dry locations.

Warm currents are red, blue currents are blue.
Figure 13.11: Gyres of the Earth’s oceans.

The Coriolis effect operates on all motions on the Earth. Artillerymen must take the Coriolis effect into account on ballistic trajectories when making long-distance targeting calculations. Geologists note how its effect on air and currents creates deserts in designated zones around the Earth as well as the surface currents in the ocean. The Coriolis effect causes the ocean to turn clockwise in the northern hemisphere and counterclockwise in the southern. It also affects by creating high-altitude, polar jet that sometimes push lobes of cold arctic air into the temperate zone, down to as far as 30° from the usual 60°. It also causes low pressure systems and intense tropical storms to rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.


Video 13.2: The Coriolis effect.

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13.2 Desert Weathering and Erosion

There is an arch and spires
Figure 13.12: Weathering and erosion of Canyonlands National Park has created a unique landscape, including arches, cliffs, and spires.

takes place in desert climates by the same means as other climates, only at a slower rate. While higher temperatures typically spur faster , water is the main agent of , and lack of water slows both mechanical and . Low levels also mean less  as well as . When  does occur in the desert, it is often heavy and may result in in which a lot of material may be dislodged and moved quickly.

The rock is dark brown with petroglyphs
Figure 13.13: Newspaper rock, near Canyonlands National Park, has many petroglyphs carved into desert varnish.

One unique product in deserts is . Also known as desert patina or rock rust, this is thin dark brown layers of clay and iron and manganese that form on very stable surfaces within arid environments. The exact way this material forms is still unknown, though cosmogenic and biologic mechanisms have been proposed.

The left of the picture is full of brown dust
Figure 13.14: A dust storm (haboob) hits Texas in 2019.

While water is still the dominant agent of in most desert environments, wind is a notable agent of and in many deserts. This includes suspended traveling in , or large dust storms, that frequent deserts. Deposits of windblown dust are called . deposits cover wide areas of the midwestern United States, much of it from rock flour that melted out of the during the last . Loess was also blown from desert regions in the West. Possessing lower energy than water, wind transport nevertheless moves sand, silt, and dust. As noted in chapter 11, the load carried by a fluid (air is a fluid like water) is distributed among and . As with water, in wind these components depend on wind velocity.

Sand grains bouncing and splashing out other grains in saltation.
Figure 13.15: Diagram showing the mechanics of saltation.

Sand size material moves by a process called in which sand grains are lifted into the moving air and carried a short distance where they drop and splash into the surface dislodging other sand grains which are then carried a short distance and splash dislodging still others.

Windblown sand grains showing rounding and frosted surfaces due to transport b wind.
Figure 13.16: Enlarged image of frosted and rounded windblown sand grains.

Since saltating sand grains are constantly impacting other sand grains, wind blown sand grains are commonly quite well rounded with frosted surfaces. is a cascading effect of sand movement creating a zone of wind blown sand up to a meter or so above the ground. This zone of saltating sand is a powerful agent in which features are effectively sandblasted. The fine-grained is effectively sorted from the sand near the surface carrying the silt and dust into . Wind is thus an effective agent separating sand and dust sized (≤70 µm) particles (see chapter 5). When wind velocity is high enough to slide or roll materials along the surface, the process is called .

A large rock has slid over the playa surface leaving a track in the mud.
Figure 13.17: A “sailing stone” at Racetrack Playa in Death Valley National Park, California.

One extreme version of movement was shrouded in mystery for years: . Also called and , these are large moving boulders along flat surfaces in deserts, leaving trails. This includes the famous example of the Racetrack in Death Valley National Park, California. For years, scientists and enthusiasts attempted to explain their movement, with little definitive results. In recent years, several experimental and observational studies have confirmed that the stones, imbedded in thin layers of ice, are propelled by friction from high winds. These studies include measurements of actual movement, as well as re-creations of the conditions, with resulting movement in the lab.

Huge sand mass that looks polished against a blue sky.
Figure 13.18: Wind-carved ventifact in White Desert National Park, Egypt.
Large rock standing on a base narrowed by sandblasting.
Figure 13.19: A yardang near Meadow, Texas.

The zone of saltating sand is an effective agent of through sand abrasion. A outcrop which has such a sandblasted shape is called a . Rocks and boulders lying on the surface may be blasted and polished by saltating sand. When predominant wind directions shift, multiple sandblasted and polished faces may appear. Such wind abraded desert rocks are called .

Photo of land level lowered by wind causing a blowout.
Figure 13.20: Blowout in Texas.

In places with sand and silt accumulations, clumps of vegetation often anchor on the desert surface. Yet, winds may be sufficient to remove materials not anchored by vegetation. The bowl-shaped depression remaining on the surface is called a .


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13.3 Desert Landforms

Looking down on semi-circular fan-shaped deposit where a stream emerges from a canyon in Death Valley
Figure 13.21: Aerial image of alluvial fan in Death Valley.

In the American Southwest, as  emerge into the valleys from the adjacent mountains, they create desert landforms called fans. When the  emerges from the narrow canyon, the flow is no longer constrained by the canyon walls and spreads out. At the lower slope angle, the water slows down and drops its coarser load. As the channel fills with this conglomeratic material, the is deflected around it. This deposited material deflects the  into a  of radial distributary channels in a process similar to how a  is made by a  entering a body of water. This process develops a of radial distributaries and constructs a fan shaped feature called an fan.

Photo of mountain where alluvial fans have coalesced into an apron of sedimant along the mountain front.
Figure 13.22: Bajada along Frisco Peak in Utah.

fans continue to grow and may eventually coalesce with neighboring fans to form an apron of along the mountain front called a .

Rounded mountain in a desert
Figure 13.23: Inselbergs in the Western Sahara.

As the mountains erode away and their accumulates first in fans, then , the mountains eventually are buried in their own erosional debris. Such buried mountain remnants are called , “island mountains,” as first described by the German geologist Wilhelm Bornhardt (1864–1946).

Satellite image of desert dry lake or playa surrounded by mountains.
Figure 13.24: Satellite image of desert playa surrounded by mountains.

Where the desert valley is an enclosed , i.e. entering it do not drain out, the water is removed by evaporation and a dry lake is formed called a .

Photo of dry wash that carries water only after rains.
Figure 13.25: Dry wash (or ephemeral stream).

are among the flattest of all landforms. Such a dry lake may cover a large area and be filled after a heavy thunderstorm to only a few inches deep. lakes and desert that contain water only after rainstorms are called intermittent or . Because of intense thunderstorms, the volume of water transported by drainage in arid environments can be substantial during a short of time. Desert soil structures lack organic matter that promotes infiltration by absorbing water. Instead of percolating into the , the  compacts the ground surface, making the  hydrophobic or water-repellant. Because of this hardpan surface, may gather water across large areassuddenly filling with water from storms many miles away.

Formerly dry wash now a violent torrent after heavy rain in the area
Figure 13.26: Flash flood in a dry wash.

High-volume  flows, called , may move as sheet flows or , as well as be channeled through normally dry or canyonsFlash floods are a major factor in desert . Dry channels can fill quickly with , creating a mass of water and debris that charges down the and even overflowing the banks.  pose a serious hazard for desert travelers because the storm activity feeding the may be miles awayPeople hiking or camping in  that have been bone dry for months, or years, have been swept away by sudden . 

13.3.1 Sand

The Sahara Desert, a sea of sand or erg.
Figure 13.27: Sahara Desert, a sand sea or erg.

The popular concept of a typical desert is a broad expanse of sand. Geologically, deserts are defined by a lack of water and arid regions resembling a sea of sand belong to the category of desert called an . An  consists of fine-grained, loose sand grains, often blown by wind, or  forces, into . Probably the best known  is the Rub’ al Khali, which means Empty Quarter, of the Arabian Peninsula. Ergs are also found in the Great Sand Dunes National Park (Colorado), Little Sahara Recreation Area (Utah), White Sands National Monument (New Mexico), and parts of Death Valley National Park (California).  are not restricted to deserts, but may form anywhere there is a substantial supply of sand, including as far north as 60° N in Saskatchewan, Canada, in the Athabasca Sand Dunes Provincial Park. Coastal  exist along lakes and oceans as well, and examples are found in Oregon, Michigan, and Indiana. 

Diagram shows wind direction moving right and sand moving the same way swooping under.
Figure 13.28: Formation of cross bedding in sand dunes.

An internal cross section of a sand shows a feature called . As wind blows up the windward side of the , it carries sand to the crest depositing layers of sand parallel to the windward (or “stoss”) side. The sand builds up the crest of the and pours over the top until the leeward (downwind or slip) face of the reaches the , the maximum angle which will support the slip face. are unstable features and move as the sand erodes from the stoss side and continues to drop down the leeward side covering previous stoss and slip-face layers and creating the cross . Mostly, these are reworked over and over again, but occasionally, the features are preserved in a depression, then lithified. Shifting wind directions and abundant sand sources create chaotic patterns of cross like those seen in Zion National Park of Utah.

Image of cross bedding in ancient sand dunes at Zion National Park, Utah.
Figure 13.29: Cross beds in the Navajo Sandstone at Zion National Park.

In the  , Utah was covered by a series of with the thickest being in Southern Utahwhich lithified into (see chapter 5). Perhaps the best known of these   is the Navajo Sandstone of age. This  formation consists of dramatic cliffs and spires in Zion National Park and covers a large part of the Colorado Plateau. In Arches National Park, a later series of sand  covered the Navajo Sandstone and lithified to become the Entrada Formation also during the . of overlying layers exposed fins of the underlying Entrada Sandstone and carved out weaker parts of the fins forming the arches. 

Windblown sand grains showing rounding and frosted surfaces due to transport b wind.
Figure 13.30: Enlarged image of frosted and rounded windblown sand grains.

As the cements that hold the grains together in these modern sand cliffs disintegrate and the freed grains gather at the base of the cliffs and move down the washes, sand grains may be recycled and redeposited. These sand may represent ancient sands recycled many times from origins in the early , just passing now through another cycle of and . An example of this is Coral Pink Sand Dunes State Park in Southwestern Utah, which contains sand that is being eroded from the Navajo Sandstone to form new .

Dune Types

Satellite image of a field of bnarchan dunes, eqach showing the fcharacteristic shape of sand wings wrapped around the bare dune court. The wionmgs point in the direction of prevailing winds.
Figure 13.31: NASA image of barchan dune field in coastal Brazil.

are complex features formed by a combination of wind direction and sand supply, in some cases interacting with vegetation. There are several types of representing variables of wind direction, sand supply and vegetative anchoring. Barchan or crescent form where sand supply is limited and there is a fairly constant wind direction. Barchans move downwind and develop a crescent shape with wings on either side of a crest. Barchans are known to actually move over homes, even towns.

Long linear parallel dune ridges that form in the direction of prevailing winds.
Figure 13.32: Satellite image of longitudinal dunes in Egypt.

 or form where sand supply is greater and the wind blows around a dominant direction, in a back-and-forth manner. They may form ridges tens of meters high lined up with the predominant wind directions.

Parabolic dunes anchored by vegetation such that wind blows out the central part and leaves sand wings pointing back from prevailing wind direction
Figure 13.33: Parabolic dunes.

form where vegetation anchors parts of the sand and unanchored parts . shape may be similar to barchan but usually reversed, and it is determined more by the anchoring vegetation than a strict parabolic form.

A dune with a central peak and many ridges formed by shifting winds
Figure 13.34: Star dune in Namib Desert.

form where the wind direction is variable in all directions. Sand supply can range from limited to quite abundant. It is the variation in wind direction that forms the star.


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13.4 The Great Basin and the Basin and Range

Map of the Great Basin occupying Utah west of the Wasatch Mountains, most of Neada, southeast Oregon and esxtending into southern California.
Figure 13.35: The Great Basin.

The Great Basin is the largest area of interior in North America, meaning there is no outlet to the ocean and all remains in the or is evaporated. It covers western Utah, most of Nevada, and extends into southeastern California, southern Oregon, and southern Idaho. Because there is not outlet to the ocean, in the Great Basin deliver to lakes and within the . A subregion within the Great Basin is the which extends from the Wasatch Front in Utah west across Nevada to the Sierra Nevada Mountains of California. The basins and ranges referred to in the name are  and , formed by  blocks from crustal , as discussed in chapter 2 and chapter 9. The of the entire area has stretched by a factor of about 2, meaning from end to end, the distance has doubled over the past 30 million years or so. Valleys without outlets form individual basins, each of which is filled with leading into . During the recent , The climate was more humid and while glaciers were forming in some of the mountains, formed covering large areas (see section 14.4.3). During the , valleys in much of western Utah and eastern Nevada were covered by Lake Bonneville. As the became arid after the , Lake Bonneville dried leaving as a remnant the Great Salt Lake in Utah.

The desert has a small town
Figure 13.36: Typical Basin and Range scene. Ridgecrest, CA sits just east of the southern Sierra Nevada Mountains.

The desert of the extends from about 35° to near 40° and results from a rain shadow effect created by westerly winds from the Pacific rising and cooling over the Sierras becoming depleted of moisture by on the western side. The result is relatively dry air descending across Nevada and western Utah.

A journey from the Wasatch Front southwest to the Pacific Ocean will show stages of desert landscape evolution from the block mountains of Utah with sharp peaks and fans at the mouths of canyons, through landscapes in Southern Nevada with along the mountain fronts, to the landscapes in the Mojave Desert of California with subdued sticking up through a sea of coalesced . These landscapes illustrate the evolutionary stages of desert landscape development.

13.4.1 Desertification

World map showing desertification vulnerability
Figure 13.37: World map showing desertification vulnerability.

When previously arable land suitable for agriculture transforms into desert, this process is called Plants and -rich  (see chapter 5) promote   and water retention. When an area becomes more arid due to changing environmental conditions, the plants and  become less effective in retaining water, creating a  loop of . This self-reinforcing loop spirals into increasingly arid conditions and further enlarges the desert regions.

may be caused by human activities, such as unsustainable crop cultivation practicesovergrazing by livestock, overuse of groundwater, and global change. Human-caused desertification is a serious worldwide problem. The world map figure above shows what areas are most vulnerable to . Note the red and orange areas in the western and midwestern regions of the United States, which also cover large areas of arable land used for raising food crops and animals. The creation of the Dust Bowl in the 1930s (see chapter 5is a classic example of a high-vulnerability region impacted by humancaused . As demonstrated in the Dust Bowl, conflicts may arise between agricultural practices and conservation measuresMitigating  while allowing farmers to make a survivable living requires public and individual education to create community support and understanding of sustainable agriculture alternatives.


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Summary

Approximately 30% of Earth’s surface is arid lands, the location of which is determined by , atmospheric circulation, and terrain. The arid belts between 15o and 30o north and south latitudes are produced by descending air masses associated with major cells in the and include the major deserts like the Sahara in Africa and the Middle East. lie behind mountain ranges or long land expanses in zones of prevailing winds like the deserts of western North America, the Atacama of South America, and the Gobi of Asia. Dry descending air also creates the at the poles.

Major atmospheric circulation involves the , midlatitude or Ferrel cells, and the in each hemisphere. Warmed and rising air in the rains back on the tropics and moves toward the poles as dryer air. That air meets the dryer equatorward moving air of the Ferrel cells. This dry air descends in the arid zones, called the horse latitudes, to produce the arid belts in each hemisphere. Rotation of the Earth creates the Coriolis Effect that deflects these moving air masses to produce zones of prevailing winds, the in the subtropics and the in the midlatitudes. A combination of , rain shadow, and cold adjacent ocean currents causes the of northern Chile, the driest desert on Earth.

in deserts takes place just as in other climes only slower because of less water. is a product unique to desert environments. As in more humid climes, water is the main agent of although wind is a notable agent. Large dust storms called transport large amounts of that may accumulate in sand seas called or finer grained deposits. Sand transport occurs mainly by in which grain to grain impact causes frosting of grain surfaces. Sandblasting by persistent winds produces stones with polished surfaces called and sculpted features called .

Landforms produced in desert environments include fans, , , and . Windblown sand can accumulate as . The forms of , like barchans, parabolic, longitudinal, and , relate to the abundance of sand supply and wind direction as well as presence of vegetation. The internal structure of shows . in an ancient desert leave in places like Zion and Arches national parks in Utah showing shifting wind directions in these ancient environments. in desert regions may carry water only after storms and pose risk of .

The Great Basin of North America is an enclosed with no to the ocean. The only exit for there is by evaporation. Travels in the Great Basin show stages of development of desert landscapes from and fans, to , to which are eroded mountains buried in their own erosional debris.

Poor land management can result in dying vegetation and loss of moisture producing an accelerating process of in which once productive land is degraded into unproductive desert. This is a serious worldwide problem.


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Text References

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Figure References

Figure 13.1: World hot deserts (Koppen BWh). Peel, M. C., Finlayson, B. L., and McMahon, T. A.; adapted by Me ne frego. 2011. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:Koppen_World_Map_BWh.png

Figure 13.2: Mountainous areas in front of the prevailing winds create a rain shadow. domdomegg. 2015. CC BY 4.0. https://commons.wikimedia.org/wiki/File:Rainshadow_copy.svg

Figure 13.3: In this image from the ISS, the Sierra Nevada Mountains are perpendicular to prevailing westerly winds, creating a rain shadow to the east (down in the image). NASA. 2003. Public domain. https://earthobservatory.nasa.gov/images/3273/southern-sierra-nevada-and-owens-lake

Figure 13.4: Generalized atmospheric circulation. NASA. 2009. Public domain. https://commons.wikimedia.org/wiki/File:Earth_Global_Circulation.jpg

Figure 13.5: USGS Map of the Great Basin Desert. USGS. 2012. Public domain. https://commons.wikimedia.org/wiki/File:Central_Basin_and_Range_ecoregion.gif

Figure 13.6: Map of the Atacama desert (yellow) and surrounding related climate areas (orange). cobaltcigs. 2010. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:Atacama_map.svg

Figure 13.7: The polar vortex of mid-November, 2013. NOAA. 2014. Public domain. https://commons.wikimedia.org/wiki/File:November2013_polar_vortex_geopotentialheight_mean_Large.jpg

Figure 13.8: In the inertial frame of reference of the top picture, the ball moves in a straight line. Hubi. 2003. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Corioliskraftanimation.gif

Figure 13.9: Forces acting on a mass moving East–West on the rotating Earth that produce the Coriolis Effect. Kindred Grey. 2022. CC BY 4.0.

Figure 13.10: Inertia of air masses caused by the Coriolis Effect in the absence of other forces. Kes47. 2015. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Coriolis_effect.svg

Figure 13.11: Gyres of the Earth’s oceans. Canuckguy; adapted by Shadowxfox and Popadius. 2012. Public domain. https://commons.wikimedia.org/wiki/File:Corrientes-oceanicas-en.svg

Figure 13.12: Weathering and erosion of Canyonlands National Park has created a unique landscape, including arches, cliffs, and spires. Rick. 2005. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Mesa_Arch_Canyonlands_National_Park.jpg

Figure 13.13: Newspaper rock, near Canyonlands National Park, has many petroglyphs carved into desert varnish. Cacophony. 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Newspaper_Rock_Full.jpg

Figure 13.14: A dust storm (haboob) hits Texas in 2019. Jakeorin. 2019. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Haboob_in_Big_Spring,_TX.jpg

Figure 13.15: Diagram showing the mechanics of saltation. NASA. 2002. Public domain. https://commons.wikimedia.org/wiki/File:Saltation-mechanics.gif

Figure 13.16: Enlarged image of frosted and rounded windblown sand grains. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:CoralPinkSandDunesSand.JPG

Figure 13.17: A “sailing stone” at Racetrack Playa in Death Valley National Park, California. Lgcharlot. 2006. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Racetrack_Playa_in_Death_Valley_National_Park.jpg

Figure 13.18: Wind-carved ventifact in White Desert National Park, Egypt. Christine Schultz. 2003. Public domain. https://commons.wikimedia.org/wiki/File:Weisse_W%C3%BCste.jpg

Figure 13.19: A yardang near Meadow, Texas. United States Department of Agriculture. 2000. Public domain. https://commons.wikimedia.org/wiki/File:Yardang_Lea-Yoakum_Dunes.jpg

Figure 13.20: Blowout in Texas. Leaflet. 1996. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Blowout_Earth_TX.jpg

Figure 13.21: Aerial image of alluvial fan in Death Valley. USGS. 2005. Public domain. https://commons.wikimedia.org/wiki/File:Alluvial_Fan.jpg

Figure 13.22: Bajada along Frisco Peak in Utah. GerthMichael. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:FriscoMountainUT.jpg

Figure 13.23: Inselbergs in the Western Sahara. Nick Brooks. 2007. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Breast-Shaped_Hill.jpg

Figure 13.24: Satellite image of desert playa surrounded by mountains. Robert Simmon, using Landsat data from the U.S. Geological Survey and NASA. 2013. Public domain. https://earthobservatory.nasa.gov/images/80913/eye-exam-for-a-satellite

Figure 13.25: Dry wash (or ephemeral stream). Finetooth. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Dry_Wash_in_PEFO_NP.jpg

Figure 13.26: Flash flood in a dry wash. USGS. 2016. Public domain. https://www.usgs.gov/media/images/a-flooded-river-australia

Figure 13.27: Sahara Desert, a sand sea or erg. Wsx. 2004. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Sahara_Desert_in_Jalu,_Libya.jpeg

Figure 13.28: Formation of cross bedding in sand dunes. David Tarailo, GSA, GeoCorps Program. 2015. Public domain. https://commons.wikimedia.org/wiki/File:Formation_of_cross-bedding.jpg

Figure 13.29: Cross beds in the Navajo Sandstone at Zion National Park. Roy Luck. 2010. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Sandstone_showing_Cross-bedding_Zion_National_Park_Utah_USA.jpg

Figure 13.30: Enlarged image of frosted and rounded windblown sand grains. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:CoralPinkSandDunesSand.JPG

Figure 13.31: NASA image of barchan dune field in coastal Brazil. NASA. 2003. Public domain. https://earthobservatory.nasa.gov/images/3889/coastal-dunes-brazil

Figure 13.32: Satellite image of longitudinal dunes in Egypt. NASA. 2012. Public domain. https://earthobservatory.nasa.gov/images/78151/linear-dunes-great-sand-sea-egypt

Figure 13.33: Parabolic dunes. Po ke jung. 2011. CC BY 3.0. https://commons.wikimedia.org/wiki/File:Parabolic_dune.jpg

Figure 13.34: Star dune in Namib Desert. Dave Curtis. 2005. CC BY-NC-ND 2.0. https://flic.kr/p/4N5Fa

Figure 13.35: The Great Basin. Kmusser; adapted by Hike395. 2022. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Great_Basin_map.gif

Figure 13.36: Typical Basin and Range scene. Matt Affolter (QFL247). 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:RidgecrestCA.JPG

Figure 13.37: World map showing desertification vulnerability. USDA. 1998. Public domain. https://commons.wikimedia.org/wiki/File:Desertification_map.png

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