Wind Action & Desert Landscapes

WIND ACTION AND DESERT LANDSCAPES

Sandip Patil LA 9106 Geology Seminar Guide: Prof. Madhukara

Geology & Geomorphology

Wind Action & Desert Landscapes

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Wind Action Circulation of air over the earth surface is due to the differential heating between the equatorial & Polar Regions, and the fact that hot air being lighter rises above the cold air. Hence air heated at the equator would rise & reach the Polar Regions, where the chilled air would descend to the equatorial regions. The simple process of rising of hot air & descending of cool air over the earth’s surface is made complex by the rotation of the earth. Rotation creates a deflecting force on the winds, known as Coriolis force. Global wind systems The Coriolis force creates a complex global wind circulation pattern. Prevailing winds are winds which come about as a consequence of global circulation patterns. These include the Trade Winds, the Westerlies, the Polar Easterlies, and the jet streams. The global wind circulation system is divided into three cells, cell A between the equator and 30° latitude, cell B between 30° and 60° latitude, and cell C between 60° and the pole. Due to heating, air at the equator rises up into the atmosphere, and leaving behind a low pressure area. Coriolis force deflects these winds to the east. When it reaches the 30° latitude, crowding of air due to reduction in surface area of earth is sufficient to create a high pressure zone, and push the air downwards. These are

Sandip Patil

Coriolis force Any matter moving freely over the earth’s surface from equator to the poles, would pass through areas having varying rotational speeds. At the equator, the rotational speed is maximum (1600km/hr) and stationary at the poles. Hence the matter would tend to travel eastwards faster than the earth’s surface. Similarly the movement from poles to the equator would be deflected westwards. Thus there is a deflection towards the right in the Northern Hemisphere & to the left in the southern Hemisphere.

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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known as horse latitudes. The descending air divides into Trade winds blowing towards the equator and completing the convection in cell A, deflected westwards, and the disorderly westerlies that spiral towards the poles in cell B, and are responsible for cyclones due to their sinuous courses. Surface winds are already blowing from the poles downwards in cell C due to cooling of air. These meet the westerlies at 60° latitude, forming a disturbed and variable zone known as Polar front. The colder polar air tends to form a wedge, becoming cloudy and a source of rain or snow, accompanied by strong winds. The polar front advances to lower latitudes in winter, and recedes to higher ones in summer, its range being wider over the oceans. Seasonal winds only exist during specific seasons. Synoptic winds are associated with largescale events such as warm and cold fronts. They include the geostrophic wind, the gradient wind, and the cyclostrophic wind. Synoptic winds occupy the lower boundary of "forecastable" winds. As a result of the Coriolis force, winds in the northern hemisphere always flow clockwise around a high pressure area and counterclockwise around a low pressure area (the reverse occurs in the southern hemisphere). At the same time, winds always flow from areas of high pressure to areas of low pressure. These two forces are opposite but not equal, and the path that results when the two forces cancel each other runs parallel to the isobars. Wind following this path is known as geostrophic wind. Winds are said to be truly geostrophic only when other forces (e.g. friction) acting on the air are negligible, a situation which is often a good approximation to the large-scale flow away from the tropics. In certain circumstances, the Coriolis force acting on moving air may be almost or entirely overwhelmed by the centripetal force. Such a wind is said to be cyclostrophic, and is characterized by rapid rotation over a relatively small area. Hurricanes, tornadoes, and typhoons are examples of this type of wind. Mesoscale winds Winds at the next lowest level of magnitude typically arise and fade over time periods too short and over geographic regions too narrow to predict with any long-range accuracy. They include such phenomena as the cold wind outflow from thunderstorms. This wind frequently advances ahead of more intense thunderstorms and may be sufficiently energetic to generate local weather of its own. Microscale winds Microscale winds take place over very short durations of time - seconds to minutes - and spatially over only tens to hundreds of metres. The turbulence following the passage of an active front is composed of microscale winds, and it is microscale wind which produces convective events such as dust devils. Though small in scope, microscale winds can play a major role in human affairs. Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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Winds by effect In classical terminology, Aeolian winds, or winds producing Aeolian action, are winds which produce geologic changes. Modern tornadoes and hurricanes might at times be considered to produce such changes. Large scale erosion, dune formation, and other geologic and topographic effects influenced by wind are still referred to as Aeolian activity. Local winds Differential heating is the motive force behind land breezes and sea breezes, also known as on- or offshore winds. Land is a rapid absorber/radiator of heat, whereas water absorbs and releases heat more slowly. Hence, in locations where sea and land meet, heat absorbed over the day will be radiated more quickly by the land at night, cooling the air. Over the sea, heat is still being released into the air at night, making it rise. This convective motion draws the cool land air in to replace the rising air, resulting in a land breeze in the late night and early morning. During the day warm air over the land rises, pulling cool air in from the sea to replace it, giving a sea breeze during the afternoon and evening. Mountain and valley breezes are due to a combination of differential heating and geometry. When the sun rises, the tops of the mountain peaks receive first light, while through the day, the mountain slopes take on a greater heat load than the valleys. This results in a temperature inequity between the two, and as warm air rises off the slopes, cool air moves up out of the valleys to replace it. This upslope wind is called a valley breeze. The opposite effect takes place in the afternoon, as the valley radiates heat. The peaks, long since cooled, transport air into the valley in a process that is partly gravitational and partly convective and is called a mountain breeze. Mountain breezes are one example of what is known more generally as a katabatic wind. These are winds driven by cold air flowing down a slope, and occur on the largest scale in Greenland and Antarctica. Because katabatic refers specifically to the vertical motion of the wind, this group also includes winds which form on the lee side of mountains, and heat as a consequence of compression. Such winds may undergo a temperature increase of 20 °C or more. Among the most well-known of these winds are the chinook of Western Canada and the American Northwest, the Swiss föhn, California's infamous Santa Ana wind, and the French Mistral. The opposite of a katabatic wind is an anabatic wind, described above as valley wind. Orographic wind refers to air which undergoes orographic lifting due to barriers like mountain ranges, and descends on the leeward sides. A notable result is high rainfall on windward slopes, and desert like landscape on the leeward side.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

The Thar Desert near Jaisalmer, High desert in Eastern India United States Deserts About one-fifth of Earth's land surface is desert. A desert is a geological region that receives little precipitation. Generally deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 inches). 'True deserts' where vegetation cover is exceedingly sparse and rainfall is exceedingly rare and infrequent, correspond to the 'hyper arid’ regions of the earth. Deserts are a part of a wider classification of regions that, on an average annual basis, have a moisture deficit (i.e. they can potentially lose more than is received). These areas are collectively called 'dry lands' and extent over almost half of the earth's land surface. Because desert is a vague term, the use of 'dry land', and its subdivisions of hyper arid, arid, semiarid and dry-sub humid, are to be preferred (as approved by the United Nations). Deserts often have high biodiversity, including animals that remain hidden during daylight hours to control body temperature or to limit moisture needs. Deserts usually have an extreme temperature range. Most deserts have a low temperature at night because the air is contains little moisture and therefore holds little heat. As soon as the sun sets, the desert cools quickly. Cloudless skies increase the release of heat at night.

Oregon,

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The Agasthiyamalai hills, creates a rain shadow region

Evapotranspiration Evapotranspiration is the combination of water loss through atmospheric evaporation, coupled with the evaporative loss of water through the life processes of plants. Potential evapotranspiration, is the amount of water that could evaporate in any given region. The water budget of an area can be calculated using the formula: “P-PE+/-S”, wherein P is precipitation, PE is potential evapotranspiration rates and S is amount of surface storage of water. Tucson, Arizona receives about 300 mm of rain per year, however about 2500 mm of water could evaporate over the course of a year, about 8 times more water than actually falls. Rates of evapotranspiration in Alaska are much lower, so while it receives minimal precipitation, it is designated as specifically different from the definition of a desert: a place where evaporation exceeds precipitation.

The most widely accepted system of classification is based on the amount of precipitation an area receives: • Extremely arid lands: at least 12 consecutive months without rainfall (deserts) • Arid lands: have less than 250 millimeters of annual rainfall (deserts) • Semiarid lands: mean annual precipitation 250 - 500 millimeters (steppes) However, a desert cannot be accurately described through lack of rainfall. For example, Phoenix, Arizona receives less than 250 millimeters (10 inches) of precipitation per year, and is immediately recognized as being located in a desert. The North Slope of Alaska's Brooks Range also receives less than 250 millimeters of precipitation per year, but is not generally recognized as a desert region. The difference lies in "potential evapotranspiration." Geographical Classification of Deserts Trade Wind Deserts: The trade winds in two belts on the equatorial sides of the Horse Latitudes heat up as they move toward the Equator. These dry winds dissipate cloud cover, allowing more sunlight to heat the land. Most of the major deserts of the world lie in areas crossed by the trade winds. The world's largest desert, the Sahara of North Africa, which has experienced temperatures as high as 57° C, is a trade wind desert. Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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Mid-Latitude Deserts: Midlatitude deserts occur between 30° and 50° latitudes, pole ward of the subtropical high pressure zones. These deserts are in interior drainage basins far from oceans and have a wide range of annual temperatures. The Sonoran Desert of southwestern North America is a typical midlatitude desert. Rain-shadow Deserts: Rain shadow deserts are formed because tall mountain ranges prevent moisture-rich clouds from reaching areas on the lee, or protected side, of the range. Air masses lose much of their moisture as they move over a mountain range. A desert is formed in the leeside "shadow" of the range. Coastal Deserts: Coastal deserts generally are found on the edges of continents near the Tropics of Cancer and Capricorn. They are affected by cold ocean currents that parallel the coast. Because local wind systems dominate the trade winds, these deserts are less stable than other deserts. Winter fogs, produced by upwelling cold currents, frequently blanket coastal deserts and block solar radiation. Coastal deserts are relatively complex because they are at the juncture of terrestrial, oceanic, and atmospheric systems. A coastal desert, the Atacama of South America, is the Earth's driest desert. In the Atacama, measurable rainfall--1 millimeter or more of rain--may occur as infrequently as once every 5-20 years. Monsoon Deserts: "Monsoon," derived from an Arabic word for "season," refers to a wind system with pronounced seasonal reversal. Monsoons develop in response to temperature variations between continents and oceans. The southeast trade winds of the Indian Ocean, for example, provide heavy summer rains in India as they move onshore. As the monsoon crosses India, it loses moisture on the eastern slopes of the Aravalli Range. The Rajasthan Desert of India and the Thar Desert of Pakistan are parts of a monsoon desert region west of the range. Polar Deserts: Polar deserts are areas with annual precipitation less than 250 millimeters and a mean temperature during the warmest month of less than 10° C. Polar deserts on the Earth cover nearly 5 million square kilometers and are mostly bedrock or gravel plains. Sand dunes are not prominent features in these deserts, but snow dunes occur commonly in areas where precipitation is locally more abundant. Temperature changes in polar deserts frequently cross the freezing point of water. This "freeze-thaw" alternation forms patterned textures on the ground, as much as 5 meters in diameter. Montane deserts: Montane deserts are arid places with a very high altitude; the most prominent example is found north of the Himalaya, in parts of the Kunlun Mountains and the Tibetan Plateau. Many locations within this category have elevations exceeding 3,000 meters. These places owe their high aridity (the average annual precipitation is often less than 40mm) to being very far from the nearest available sources of moisture. Vegetation Most desert plants are drought- or salt-tolerant, such as xerophytes. Some store water in their leaves, roots, and stems. Other desert plants have long tap roots that penetrate to the water table if present. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion. Even small fungi and microscopic plant organisms found on the soil surface can be a vital link in preventing erosion and providing support for other living organisms. Deserts typically have a plant cover that is sparse but enormously diverse. The Sonoran Desert of the American Southwest has the most complex Flora of Baja California Desert, Cataviña ,Mexico desert vegetation on Earth. The giant saguaro Sandip Patil Department of Landscape Architecture, CEPT University LA - 9106

Geology & Geomorphology

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cacti provide nests for desert birds and serve as "trees" of the desert. Saguaro grows slowly but may live 200 years. When fully grown, saguaro is 15 meters tall and weighs as much as 10 tons. Although cacti are often thought of as characteristic desert plants, other types of plants have adapted well to the arid environment. They include the pea and sunflower families. Cold deserts have grasses and shrubs as dominant vegetation. Water Rain does fall occasionally in deserts, and desert storms are often violent. A record 44 millimeters of rain once fell within 3 hours in the Sahara. Though little rain falls in deserts, deserts receive runoff from ephemeral, or short-lived, streams fed considerable quantities of sediment for a day or two. Although most deserts are in basins with closed or interior drainage, a few deserts are crossed by 'exotic' rivers that derive their water from outside the desert. Such rivers infiltrate soils and evaporate large amounts of water on their journeys through the deserts, but their volumes are such that they maintain their continuity. The Nile River, the Colorado River, and the Yellow River are exotic rivers that flow through deserts to deliver their sediments to the sea. Deserts may also have underground springs, rivers, or reservoirs that lay close to the surface, or deep underground. Plants that have not completely adapted to sporadic rainfalls in a desert environment may tap into underground water sources that do not exceed the reach of their root systems. Lakes form where rainfall in interior drainage basins is sufficient. Desert lakes are generally shallow, temporary, and salty. Because these lakes are shallow and have a low bottom gradient, wind stress may cause the lake waters to move over many square kilometers. When small lakes dry up, they leave a salt crust or hardpan. The flat area of clay, silt, or sand encrusted with salt that forms is known as a playa. When the occasional precipitation does occur, it erodes the desert rocks quickly and powerfully. Winds are the other factor that erodes deserts - they are constant yet slow. Mineral resources Some mineral deposits are formed, improved, or preserved by geologic processes that occur in arid lands as a consequence of climate. Ground water leaches ore minerals and redeposits them in zones near the water table. This leaching process concentrates these minerals as ore that can be mined. Evaporation in arid lands enriches mineral accumulation in their lakes. Playas may be sources of mineral deposits formed by evaporation. Water evaporating in closed basins precipitates minerals such as gypsum, salts (including sodium nitrate and sodium chloride), and borates. The minerals formed in these evaporite deposits depend on the composition and temperature of the saline waters at the time of deposition. The Atacama Desert of South America is unique among the deserts of the world in its great abundance of saline minerals. Sodium nitrate has been mined for explosives and fertilizer in the Atacama since the middle of the 19th century. Nonmetallic mineral resources and rocks such as beryllium, mica, lithium, clays, pumice, and scoria occur in arid regions. Sodium carbonate, sulfate, borate, nitrate, lithium, bromine, iodine, calcium, and strontium compounds come from sediments and near-surface brines formed by evaporation of inland bodies of water, often during geologically recent times. Some of the more productive petroleum areas on Earth are found in arid and semiarid regions of Africa and the Mideast, although the oil fields were originally formed in shallow marine environments. Recent climate change has placed these reservoirs in an arid environment. Other oil reservoirs, however, are presumed to be Aeolian in origin and are presently found in humid environments. Desert Landscapes Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called Reg or hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation. Bottom lands may be saltcovered flats. Aeolian processes are major factors in shaping desert landscapes. Cold deserts have similar features but the main form of precipitation is snow rather than rain. Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Being dry, deserts are ideal places for human artifacts and fossils to be preserved. Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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Sand covers only about 20 percent of Earth's deserts. Most of the sand is in sand sheets and sand seas. There are 6 forms of deserts: • Mountain and basin deserts; • Hamada deserts, which comprise of plateau landforms; • Regs which consist of rock pavements; • Ergs which are formed by sand seas; • Intermontane Basins; and • Badlands located at the margins of arid lands comprising of clay-rich soil. Nearly all desert surfaces are plains where Aeolian deflation has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles. The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. Bedrock outcrops commonly occur as small mountains surrounded by extensive erosional plains. Aeolian Processes Aeolian processes pertain to the activity of the winds and are commonly referred to as wind erosion. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation and a large supply of unconsolidated sediments. Although water is much more powerful than wind, Aeolian processes are important in arid environments such as deserts. Aeolian erosion By itself, wind can only remove dry deposits. This process is known as deflation, as a result of which the land surface is lowered. The sand grains thus acquired by wind near the ground surface, become powerful agents of erosion, a process known as abrasion. Wind thus erodes the Earth's surface by deflation and abrasion. Deflation is the lifting and removal of loose, fine-grained particles, as a result of the turbulent eddy action of the wind. Almost half of Earth's desert surfaces are stony deflation zones and have desert pavement landscape. The rock mantle in desert pavements protects the underlying material.

The sand and rock of China's Turpan Depression

Blow Outs Deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Sand grains are rolled or skipped along the surface and comprise the bed load. In such a way, the entire bed is lowered, in some cases up to one metre, resulting in shallow depressions called blowouts. This depression may be a few metres to as much as a kilometer across. Blowouts are also found on rock surfaces subjected to disintegration by weathering. Abrasion is the wearing down of surfaces by the grinding action and sand blasting of windborne particles. Larger particles are rounded, but the finer particles, about 0.06-0.2mm in diameter, are usually angular. Winnowing action of wind sorts these particles according to their sizes. Wind-driven grains abrade landforms. Grinding by particles carried in the wind creates grooves or small depressions and creates ventifacts. Sculpted landforms, called yardangs, up to tens of meters high and kilometers long are streamlined by desert winds. The famous sphinx at Giza in Egypt is believed to be a modified yardang.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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Undercutting is a marked feature of wind abrasion, being most effective within 30-60 cms of the surface where saltating sand is abundant. Alcoves and caverns may be hollowed along the base of escarpments. Rocks formed by undercutting are known as Pedestal Rock. Joints are attacked and opened up, forming outlines of Rock Towers or pinnacles, left isolated near receding walls of escarpment.

Cathedral Spire, Garden of Gods, USA

Undercutting, Arches National Park, USA

Aeolian transportation Particles are transported by winds through suspension, saltation, and creep. Small particles may be held in the atmosphere in Suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air. Typical winds near Earth's surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze. Saltation moves small particles in the direction of the wind in a series of short hops or skips. Sand-size particles are lifted no more than one centimeter above the ground, and are transported at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. Surface creep accounts for as much as 25 percent of grain movement in a desert. Saltating grains hit larger grains that are too heavy to hop, but creep forward as they are pushed forward. Transportation generally follows the following pattern: Dust smaller particles Sand medium particles Pebbles larger particles Sandip Patil

suspension saltation creep

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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Dust Storm Aeolian turbidity currents are better known as dust storms. Air over deserts is cooled significantly when rain passes through it. This cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward and sweeps up surface debris in its turbulence as a dust storm. Dust storms blowing over desert surfaces lift great quantity of fine dust into the air. As much as a thousand metric tones of dust may be suspended in a cubic kilometer of air. Dust from a single storm may be traced as much as four thousand kilometers away. In the Thar Desert, continued trampling of fine textured soils produces a blanket of dusty hot air that hangs over the region for a long period, and may extend upto nine kilometers into the atmosphere. Crops, people, villages, and possibly even climates are affected by dust storms. Some dust storms are intercontinental, a few may circle the globe, and occasionally they may engulf entire planets. Small whirlwinds, called dust devils, are common in arid lands and are thought to be related to very intense local heating of the air that result in instabilities of the air mass. Dust devils may be as much as one kilometer high. Aeolian Deposition Wind-deposited materials hold clues to past as well as to present wind directions and intensities. These features help us understand the present climate and the forces that molded it. Wind-deposited sand bodies occur as sand sheets, ripples, and dunes. Sand Sheets Sand sheets are flat, gently undulating sandy plots of sand surfaced by grains that may be too large for saltation. They are expanses of horizontally laid Aeolian sand devoid of dunes. The surface is usually rippled. Pits generally display layers of two distinct grain sizes. This is due to the fact that larger grains are transported by creep, while smaller ones saltate. Dunes are absent due to presence of strong winds, and if the winds are sand-laden, even ripple formation is suppressed. Sand sheets are formed on borders of deserts having scanty vegetation. Movement of sand may be suppressed by desert pavements, vegetation, etc. Sand sheets form approximately 40 percent of Aeolian depositional surfaces. The Selima Sand Sheet, which occupies 60,000 square kilometers in southern Egypt and northern Sudan, is one of the Earth's largest sand sheets. The Selima is absolutely flat in some places; in others, active dunes move over its surface. Ripples Wind blowing on a sand surface ripples the surface into crests and troughs whose long axes are perpendicular to the wind direction. The average length of jumps during saltation corresponds to the wavelength, or distance between adjacent crests, of the ripples. In ripples, the coarsest materials collect at the crests. This distinguishes small ripples from dunes, where the coarsest materials are generally in the troughs.

Wind-blown sand moves up the gentle upwind side of the dune by saltation or creep. When the buildup of sand accumulating at the top of the slipface at the brink exceeds the angle of repose, a small avalanche of grains slides down the slipface. Grain by grain, the dune moves downwind.

Accumulations of sediment blown by the wind into a mound or ridge, dunes have gentle upwind slopes on the wind-facing side. The downwind portion of the dune, the lee slope, is commonly a steep avalanche slope referred to as a slipface. Dunes may have more than one slipface. The minimum height of a slipface is about 30 centimeters.

Oasis As sand is blown across flat desert plains, it may scour out hollows where the rocks are softer. However, the depth of these depressions is restricted by presence of underground water. If a water soaked layer is reached, the particles of sand will bind together. They will be too heavy to be carried or picked up by wind. Vegetation will start appearing, creating the rare landscape of oasis. Oases are Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. Oases are often the only places in deserts that support crops and permanent habitation. Loess Loess is an accumulation of winnowed dust transported by wind. Most of the dust carried by dust storms is in the form of silt-size particles. The thickest known deposit of loess, 335 meters, is on the Loess Plateau in China. In Europe and in the Americas, accumulations of loess are generally from 20 to 30 meters thick. Particles in loess vary between 0.01-0.05 mm. Some loess may be washed down by rain, although they are most common where wind loses velocity, eg. Wind over mountains entering plains.

Loess Deposits

Desert Varnish Desert varnish is a dark coating on rocks found in arid regions, composed dominantly of fine-grained clay minerals containing black manganese oxide and red iron oxide. Varnish can be a prominent feature in many landscapes. It often coats canyon walls. Earlier it was believed varnish was made from substances drawn out of the rocks it coats. Microscopic and observations show that a major part of varnish is clay which could only arrive by wind. Clay acts as a substrate to catch additional substances that chemically react together when the rock reaches high temperatures in the desert sun. Wetting by dew is also important in the process. Desert varnish has a high concentration of manganese, 50 to 60 times more abundant than elsewhere. This enrichment is thought to be caused by biochemical processes (many species of bacteria use manganese). The clay minerals represent the clays found locally in the region where the varnish develops. Black manganese oxide (birnesite) and red iron oxide (hematite) add color. Desert varnish forms only on physically stable rock surfaces that are no longer subject to frequent precipitation, fracturing or sandblasting.

Desert Varnish

Pteroglyphs have been created by chipping away varnish to expose lighter rock & thus draw. (Photo: Indian Pteroglyph Park, New Mexico, USA.)

Desert varnish often obscures the identity of the underlying rock, and different rocks have varying abilities to accept and retain varnish. Limestones, for example, typically do not have varnish because they are too water soluble and therefore do not provide a stable surface for varnish to form. Shiny, dense and black varnishes form on basalt, fine quartzites and metamorphosed shales due to these rocks' relatively high resistance to weathering. Desert Pavement A desert pavement is a desert surface that is covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size, formed by the gradual removal of the sand, dust and other fine grained material by the wind and intermittent rain. Frequently the stones are polished by the Sandip Patil Department of Landscape Architecture, CEPT University LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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abrasion of wind-borne dust and may even be shaped by the wind, becoming ventifacts. Desert pavement surfaces are often coated with desert varnish. Desert pavements are only one or two fragments thick that form a mosaic in a matrix of fine sediment. Coarse fragments are alluvial pebbles, gravel, and cobbles, or debris weathered from bedrock. Desert pavements cover areas ranging from a few square meters to hundreds of square kilometers. They occur mostly in sand-poor regions, such as desert plains Dreikanter (Ventifacts) near bedrock outcrops, on plateaus, in dry wadis and Isolated pebbles or rock fragments lying terraces, and on alluvial fans. Evolution of the surface is on the desert surfaces are beveled on due to accretion And deflation due to wind action, water sorting, and windward side until a smooth surface is upward migration of coarse particles by freezing/thawing cut. If the direction of wind changes or by wetting/drying cycles. seasonally, or pebble is shifted by some Some older pavement areas are remarkably smooth and flat with no large fragments protruding above the surface. Such areas are commonly found on smaller fans; low, arched fans; outer reaches of large fans and outwash flats; terraces and flood plains along drainage courses. In young pavement areas, many of the larger fragments are cobbles and boulders about 15 to 30 cm across or larger, which protrude significantly above the surrounding terrain. Exposed surfaces of the coarse fragments are commonly coated with desert varnish. Little vegetation is present except where soils have developed beneath the pavement.

means, more than one face is cut in, and each pair meets in a sharp edge.

Diagram representing the various landscapes created in the deserts.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Desert Pavement

Wind Action & Desert Landscapes

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Salt lake and evaporite basins in Qaidam Depression, China (highest desert in the world)

Salt pan Salt pan is a flat expanse of ground covered with salt and other minerals, usually shining white under the sun, where water pools when it rains. A salt pan would be a lake or a pond if it was in a location in a climate where the rate of water evaporation wasn't faster than the rate of water precipitation. If the water is unable to drain into the ground, it sits on the surface until it evaporates. When the water evaporates, it leaves behind whatever minerals were dissolved in it. Over thousands of years, the minerals accumulate until the surface is white with it. Salt pans can be dangerous. The crust of salt can conceal a quagmire of mud that can engulf a truck. The Qattara Depression in the eastern Sahara desert contains many such traps. High salinity will also lead to a unique flora and fauna in the lake in question. If the amount of water flowing into a lake is less than the amount evaporated, the lake will eventually disappear and leave a salt flat or playa. Playa Playa is a dry lake-bed, generally the shore of, or remnant of, an endorheic lake. An endorheic basin is a watershed from which there is no outflow of water, either on the surface as rivers, or underground by flow or diffusion through rock or permeable material. Any precipitation that falls in such a basin remains there permanently, leaving the system only by evaporation. Playa consists of fine-grained sediments infused with alkali salts. Their surface is generally very dry, hard and smooth in the summer months, but wet and very soft in the winter months. While the playa itself will be devoid of vegetation, they are commonly ringed by salt-tolerant plants that provide critical winter fodder for herbivores. Many playas contain shallow lakes in the winter, especially during wet years. If the layer of water is thin and is moved around the playa by the wind, an exceedingly hard and smooth surface can develop. Thicker layers of water can result in a "cracked-mud" surface.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes

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A playa lake in the Thar Desert, Rajasthan, India.

Yardang A yardang is a rock ridge feature caused by wind and water erosion found in deserts and may form very unusual shapes. Yardangs form as the result of preferential erosion of surrounding media. In desert environments, mildly cemented "cores" of sediment form the basis for the structure. Loose sediment surrounding the cemented section erodes faster, leaving the core behind. Yardangs are elongate, with their long axis parallel to the Yardangs of Lut desert, Iran. (Largest on the earth) prevailing wind direction. One side is almost always steeper than the other, similar to the shape of a dune. However, in yardangs the blunt, steeper side is the windward side while the shallower slope is on the leeward side. Yardangs are classified on basis of size as: • Mega-yardangs can be several kilometers long and hundreds of meters high. A large concentration of mega-yardangs is found near the Tibesti Mountains in the central Sahara. • Meso-yardangs are generally a few meters high and 10 to 15 meters long. They are more common, and can be found throughout the Sahara. • Micro-yardangs are only a few centimeters high. Alluvial Fan An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial fan. Owing to the slowing of flow any solid material carried by the water is dropped. As this reduces the capacity of the channel, the channel will change Sandip Patil

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direction over time, gradually building up a slightly mounded or shallow conical fan shape. The deposits are in general poorly-sorted. Plants are often concentrated at the base of alluvial fans and many have long tap roots (30-50 feet) to reach water. The long-rooted plants are called phreatophytes. The water at this level is derived from water that has seeped through the fan and hit an impermeable layer that funneled the water to the base of the fan where it is concentrated and sometimes forms springs and seeps if the water is close enough to the surface.

Pediment Any relatively flat surface of bedrock (exposed or veneered with alluvial soil or gravel) that occurs at the base of a mountain or as a plain having no associated mountain is known as a pediment. Pediments, sometimes mistaken for groups of merged alluvial fans, are most conspicuous in basin-and-range-type desert areas throughout the world. The angle of a pediment's slope is generally from 0.5° to 7°. Its form is slightly concave, and it is typically found at the base of hills in arid regions where rainfall is irregular and intense for brief periods of time. There is frequently a sharp break of slope between the pediment and the steeper hillside above it. Water passes across the pediment by laminar sheet flow, but if this is disturbed, the flow becomes turbulent and gullies develop.

Pediment

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Inselberg Weathering and dissection consumes almost all the mountains over a period of time. Mountains are reduced to a few large bedrock knobs projecting above surrounding pediment and sediment filled basin, known as an inselberg.

Ayer’s Rock, Australia

Mesa In arid regions, erosion strips away successive rock layers, leaving behind plateaus capped by hard rock layers. Cliffs retreat near perpendicular surfaces since weak shale formations exposed at cliff base are rapidly washed away by storm runoff. When weakened, the rock in the upper cliff face breaks away along vertical joint fractures, producing mesas. A mesa can also be described as a table topped plateau bordered on all sides by cliffs. Butte A mesa reduced in area by retreat of cliffs forming the rim, it maintains the top. This retained landform is butte, and may collapse over a period of time. Mesas and buttes are erosional landforms created by water, and seen prominently in Monument Valley in USA.

Sandip Patil

Department of Landscape Architecture, CEPT University

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Sand Deposition Factors controlling the form of sand accumulations are: ƒ Nature, extent and rate of erosion of sediment source ƒ Sizes of sand grains and associated fragments ƒ Strength, variance, duration and direction of wind ƒ Texture of transportation and deposition surfaces Three main forms of sand deposition are: ƒ Sand Drifts in form of cliff shadow regions, protruding rocks or vegetation ƒ Dunes, transverse and longitudinal ƒ Sand sheets in interdune and extradune areas Sand Dunes A dune is a mound or ridge of wind-blown sand rising to a definite summit or crest. Bare dunes are subject to shifting location and size based on their interaction with the wind. The "valley" or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes. Dunes have a remarkable capability to collect sand from nearby areas. Sand is transported over relatively hard and smooth interdune areas more readily than over dunes where wind experiences drag. Thus saltating sand is blown obliquely towards existing dunes and intervening surface is swept bare. This factor also dictates the shape of the dune. Dunes also form under the action of water flow (alluvial processes), on sand or gravel beds of rivers, estuaries and the sea-bed. The word 'dune' derives from a medieval Germanic word - "dun", a hill. Dunes are classified on the basis of shape as: Transverse Dunes These dunes have a long, low- angle windward slope rising to a crest. A much steeper leeward slope is formed by sand coming to rest at its natural angle of repose of about 34° in the wind shadow part. When sand accumulates further, there is an avalanche wherein the coarsest and roundest grains surface and travel farthest, while the slope, known as slip-face, is reduced to 30°. Ripple is a low angle climbing deposition seen over sand sheets and transverse dunes. Cross winds may form large ripples across slip-face.

Crescentic Dunes The most common dune form on Earth is the crescentic. Mounds generally are wider than long. The slipface is on the dune's concave side. These dunes form under winds that blow from one direction. If the sand is short in supply, a series of smaller cresent shaped dunes known as barchans are formed. They may migrate through continuous transport of sand, towards the leeward directions. Some types of crescentic dunes move faster over desert surfaces than any other type of dune. A group of dunes moved more than 100 meters per year in China's Ningxia Province. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometers, are in China's Taklamakan Desert. Longitudinal Dunes Longitudinal dunes elongate parallel to the prevailing wind, caused by a larger dune having its smaller sides blown away. They are sharp-crested and common in the Sahara. They range up to 300 m in height and 300 km in length. They are thought to develop from barchans if a change of wind direction occurs. The new wind direction will lead to the development of a new wing and the overdevelopment of one of the original wings. If the prevailing wind then becomes dominant for a lengthy period of time the dune will revert to its barchan form, with one exaggerated wing. Should the strong wind then return the exaggerated wing will further extend so that eventually it will be supplied with sand when the prevailing wind returns. The wing will continue to grow under both wind conditions, thus producing a seif dune. On a seif dune the slip face develops on the side facing away from the strong wind. Linear Dunes Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometers long. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors. Some linear dunes merge to form Y-shaped compound dunes. Many form in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement. Sandip Patil Department of Landscape Architecture, CEPT University LA - 9106

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Star Dunes Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 meters tall and may be the tallest dunes on Earth. Dome Dunes Oval or circular mounds generally lacking a slipface, dome dunes are rare and occur at the far upwind margins of sand seas. Parabolic Dunes U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts. Unlike crescentic dunes, their crests point upwind. The elongated arms of parabolic dunes follow rather than lead because they have been fixed by vegetation, while the bulk of the sand in the dune migrates forward.

Barchans

Longitudinal Dunes

Parabolic Dunes Linear Dunes

Star Dunes

Transverse Dunes

Sandip Patil

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Reversing Dunes Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions. All these dune shapes may occur in three forms: simple, compound, and complex. Simple dunes are basic forms with a minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed, and complex dunes are combinations of two or more dune types. A crescentic dune with a star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed. Dune types Sub-aqueous dunes Sub-aqueous (underwater) dunes form on a bed of sand or gravel under the actions of water flow. They are commonly found in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as the upstream slope is eroded and the sediment deposited on the downstream or lee slope. These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding. Lithified dunes A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or eolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the hue of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns. Coastal dunes Dunes form on coasts where the backshore can support and onshore winds encourage the accumulation of sand blown inland from off a beach. Any part of the upper beach, once dry, can lose sand to the wind, especially if the sand is fine, and dune formation proceeds in the direction towards which the predominant wind direction is blowing. Deposition may start when sand is trapped behind surface irregularities or vegetation. Dunes provide privacy and shelter from the wind. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most such cases the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Sand Dune Arch Arches are a kind of desert formation found in the Arches National Park in USA. The national park lies atop an underground salt bed, which is basically responsible for the arches and spires, balanced rocks, sandstone fins, and eroded monoliths in the area. Thousands of feet thick in places, this salt bed was deposited over the Colorado Plateau some 300 million years ago when a sea flowed into the region and eventually evaporated. Over millions of Delicate Arch, Arches National Park, USA Sandip Patil Department of Landscape Architecture, CEPT University LA - 9106

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years, the salt bed was covered with residue from floods and winds and the oceans that came in intervals, much of which was compressed into rock. Salt under pressure is unstable, and the salt bed below was no match for the weight of this thick cover of rock. It shifted, buckled, liquefied, and repositioned itself, thrusting the earth layers upward into domes. As this subsurface movement of salt shaped the earth, surface erosion stripped away the younger rock layers. Over time water seeped into the superficial cracks, joints, and folds of these layers. Ice formed in the fissures, expanding and putting pressure on surrounding rock, breaking off bits and pieces. Winds later cleaned out the loose particles. A series of free-standing fins remained. Wind and water attacked these fins until, in some, the cementing material gave way and chunks of rock tumbled out. Many damaged fins collapsed, while others, with the right degree of hardness and balance, survived despite their missing sections, forming arches. Desertification One of the biggest problems posed by sand dunes is their encroachment on human habitats. Sand dunes move through a few different means, all of them helped along by wind. One way that dunes can move is through saltation, where sand particles skip along the ground like a rock thrown across a pond might skip across the water's surface. When these skipping particles land, they may knock into other particles and cause them to skip as well. With slightly stronger winds, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of meters through such sheet flows. And like snow, sand avalanches, falling down the steep slopes of the dunes that face away from the winds, also moving the dunes forward. Conservation Dune habitats provide niches for highly specialized plants and animals, including numerous rare and endangered species. Due to human population expansion dunes face destruction through recreation and land development, as well as alteration to prevent encroachment on inhabited areas. Some countries, notably the USA and Great Britain have developed extensive programs of dune protection.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

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Wind Action & Desert Landscapes

Annexure 1:

20

Kalahari Desert

Located in southern Africa, the Kalahari covers an area of over 700,000sq km (270,300sq miles). Stretching over parts of Namibia, South Africa and much of Botswana, its high altitude at 500l,500m (l,600^4900ft) means that the coldest nights can be extreme. The highlands of Angola and the Okavango river valley form a border to the north, while South Africa's Orange River is a southern boundary. The Kalahari is the world's second largest protected area. The sun bakes the Kalahari region for most of the year. Massive rippled sand dunes and vast, featureless dry lakes make up much of the landscape. The whole area is essentially semi-desert and supports a surprising range of wildlife. Summer rains in the north bring life-giving water to the Okavango River which forms a swampy network of lakes and lagoons, carpeting the land with vegetation. The lush north also attracts herds of grazing animals, and hence hunters such as wild dogs, hyenas and lions. Herds of wildebeest, springbok, gemsbok, eland and zebra travel vast distances through the Kalahari Desert. The breeding of many species coincides with the wet season, when food is more plentiful for their offspring. Although some herds may stay around the fringes of flood water, many head south at the beginning of the rainy season in October to avoid the flooding and search for the leaves and grasses that will provide them with essential moisture. In April, they brave the threat from predators and the harsh drought conditions, and begin their journey north again. Plant Food and Shelter The scrubby terrain and clumps of tough, lowgrowing grasses typify the desert landscape of the southern Kalahari. In the hottest, most inhospitable regions, only plants with deeper or tuber-like roots manage to survive, providing food for the toughest or most adaptable desert animals. Some plants have even adapted to the drought conditions by germinating and producing seeds within four weeks of a rain shower. With its melon-like fruit, the tsamma is a vital creeping plant for animals seeking moisture. In the central area, thornbushes and acacia trees grow more abundantly. The white-browed sparrow weaver resourcefully makes grass stem nests over the prickly spikes of one species of acacia - the winter-thorn tree - and is happy to share its home with up to a hundred other pairs of weavers. The rains of the northern Kalahari ensure the growth of African ebony, Sandip Patil

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sycamore, fig and the ancient baobab tree with its many trunks. These woodlands with their lush vegetation attract wonderfully varied wildlife, such as lions, elephants, giraffes and antelopes. Huge termite mounds a few metres high break up the sparse southern landscape of the Kalahari. In some areas they form island towers of baked earth, where the rest of the desert's softer soil and sand has eroded during the rainy months. The termites' muItichambered nests house several million members, and have airconditioned towers and an elaborate system of interconnecting underground tunnels. In their highly structured societies, termites organize a division of labour with strictly defined duties. Foragers find food, construction workers help build and repair the nest, soldiers protect the colony from attack and nurses tend the young. At the heart of this empire lies the immense single queen, lying deep in the mound away from danger. HABITAT

CLIMATE BIODIVERSITY HABITAT

Semi-arid; extensive sandy plains, dunes and salt pans; trees, scrub, grasses; south much sparser than north Low rainfall; hottest period December-March, up to 46°C;-14°C at coldest Great range of adaptable wildlife, especially in the north Stable

The lack of regular rain has always posed a challenge to the San or Bushmen of the Kalahari. They survived by gathering food and hunting game on foot with simple hunting tools, such as bows and arrows with poisoned tips. Women and children gather fruit and nuts, as well as roots and tubers from desert plants. Some of the older hunting traditions have Wildebeest are hunted by the San, hunter-gatherers of the Kalahari, who have replaced the traditional poison-tipped arrow with the shotgun. Illegal hunting, for example of elephants for ivory, is a problem even the Danger of Flooding. Now one of the two great African desert areas, the Kalahari was fertile in prehistoric times. Global warming is a possible future danger for plant and animal species. If the floodplains of the Okavango delta north of the Kalahari are inundated, many species will be seriously affected. Heavier rains in the northern regions change local habitats, the delicate balance of the region and its wildlife will be upset.

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

Wind Action & Desert Landscapes Annexure 2:

22

Namib Desert

The Namib is a long, narrow coastal desert 1,300km long and 30-140km wide on the southwestern coast of Africa. Covering the entire coastline of Namibia, it reaches north into Angola and south into South Africa. It is one of the most arid places on earth but not the hottest, the cold ocean currents and sea fogs acting as cooling agents. Washed by the Atlantic Ocean, the Namib Desert is a land of contrasts. The Kuiseb River divides the rocky plains of the north from the sands of the south which contain some of the world's tallest dunes. The sun beats down by day but without the cover of cloud to trap the day's heat, night temperatures plummet. Few mammals are year-round residents of the Namib but those that tough it out include the short-tailed rock hare, the gerbi! and the springbok, an antelope adapted to survive in drought conditions. But perhaps the most specialized of all is Grant's golden mole which is found nowhere else. Living in the dunes, this insecl eater is an expert burrower which seems to swim through the sand. During November and December Africa's largest carnivore, the lion, moves into the Namib to prey on the newborn pups of the Cape fur seal, closely followed by brown hyenas and jackals who squabble over the leftovers. Among the most ingenious of the Namib's invertebrates are the dune beetles. They leave their hideyholes on cold, foggy mornings to climb to the top of a dune. Facing the sea, they bend their heads to the sand and wait for the fog's moisture to condense into droplets on their bodies and roll down to their mouths. The antlion larva digs pits in the sort sand and waits for ants to drop in to supply it with lunch. If an ant tries to escape it is blasted with sand. The golden wheel spider escapes its predators by tucking itself into a ball and rolling down a dune away from trouble. A surprising number of plants grow in the Namib. The secret of their success is the ability to wait for rain or to store enough moisture to keep them going. Dotted ail over the desert is the welwitschia, which is thought to live for up to 2,000 years and grows nowhere else. Special pores open to receive condensed fog water which is then routed quickly to the stem for storage. Many desert plants' seeds have a special coating that keeps them viable underground; only a really good soaking will wash the coating off and allow them to sprout. It is often years before they come alive but when they do the desert is briefly turned into a blaze of colour. Few amphibians can tolerate the dry desert but the African bullfrog copes by burying itself in the mud of a drying river bed and sleeping, sometimes for years, wrapped in a bag thai it excretes from its skin. As soon as enough rain falls, it eats the bag and embarks on a frenzy of feeding and mating. But it is the reptiles that predominate here, such as the shovel-nosed lizard which has fringed feel to help it move easily across the sand.

Sandip Patil

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The plumage of most birds living in such an open habitat has to act as camouflage against predators like chanting goshawks and other raptors. Difficult to see until it moves is the dune-dwelling Gray's lark. But the real master of disguise is the bustard, which has several other features that equip it for life in the Namib. It is equally at home in the heat and cold and, like Gray's lark, eats almost anything without the need to drink. But probably its biggest asset is the ability to see through the camouflage of prey and predators. HABITAT CLIMATE BIODIVERSITY

Sandy and gravelly coastal desert Maximum temperature 35°C (95°F) in high summer; annual average 16-18°C{61-64°n. Nights much cooler Many endemic species of flora and fauna specially adapted to cope with arid conditions.

Until its independence in 1990, Namibia was controlled by South Africa which resettled some of its black population along the northeastern fringes of the Namib Desert. This policy continued until the end of the 1970s, by which time overexploitation of the land by the new settlers resulted in much of it becoming useless. One of its effects was the decline of some of the desert's wildlife including Ruppell's bustard. In the south along the Diamond Coast problems still exist for the dune animals as mining for precious gems and uranium continues to put pressure on them. Much of the Namib Desert is now a national park known as the Namib-Naukluft. At nearly 50,000 sq km, it extends from the Angolan border in a narrow strip along the length of the Skeleton Coast to an area around Walvis Bay. South of Walvis Bay the park extends inland to encompass some of the semiarid regions and as far south as Luderitz. Due to the persuasive powers of an entomologist studying Namib beetles, the park is home to a research institute to study the wildlife.

Sandip Patil

The Skeleton Coast was so named because bones of shipwrecked sailors once scattered its shores.

The elephant's foot plant germinates during storms, sending down a root in just one day and growing rapidly, it may then not grow again for years.

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Annexure 3: A list of major deserts of the world Africa: • Sahara – in northern Africa. The world's largest desert after Antarctica. • Kalahari – desert in southern Africa. • Namib – desert in southern Africa. Antarctica: • Antarctica The interior of the continent is the world's largest desert. Asia: • Gobi – desert of Mongolia. • Taklamakan – desert in China. • Ordos – desert of China. • Taklamakan – Xinjiang Uighur Autonomous Region of the People's Republic of China. • Kara Kum – deserts in Central Asia. • Kyzyl Kum – Kazakhstan and Uzbekistan. • Thar-Cholistan desert in India and Pakistan. Australia: • Gibson Desert – central Australia • Great Sandy Desert – northwestern Australia • Great Victoria Desert – central Australia • Simpson Desert – central Australia • Tanami Desert – northern Australia • Little Sahara – Kangaroo Island, South Australia Europe: • Tabernas Desert – Almería, Spain • Bledowska Desert – Lesser Poland Voivodeship, Poland • Pooma Desert Holland • Davit Gareji – Kakheti, Georgia Latin America: • La Guajira Desert – in northern Colombia and some of northwestern Venezuela. • Atacama – desert in Chile. The driest desert on Earth. • Patagonian Desert. Middle East: • Al-Dahna Desert – west of the Eastern Province, Saudi Arabia • Dasht-e Kavir – central Iran. • Dasht-e Lut – southeastern Iran. • Empty Quarter, Arabian Peninsula – the world's largest sand desert • Judean Desert – eastern Israel and West Bank. • Nefud Desert – northern Saudi Arabia • Negev – southern Israel • Desert of Sin / Zin Desert (Bible usage) – Sinai Peninsula. North America: • Mojave desert. • Great Basin desert. • Sonoran desert. • Chihuahuan desert.

Sandip Patil

Department of Landscape Architecture, CEPT University

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25

Annexure 4: Names for specific winds in certain regions In ancient Greek mythology, the four winds were personified as gods, called the Anemoi. These included Boreas, Notos, Euros, and Zephyros. The Ancient Greeks also observed the seasonal change of the winds, as evidenced by the Tower of the Winds in Athens. In modern usage, many local wind systems have their own names. For example: Alizé Alizé Maritime Amihan Bayamo Bora Chinook Etesian/Meltemi Föhn Fremantle Doctor Gilavar Gregale Habagat Harmattan Halny Khamsin Khazri Kosava Levanter Libeccio Marin Mistral Nor'easter Nor'wester Santa Ana winds Simoom Sirocco Southerly Buster Tramontane Vendavel Zonda wind

(northeasterly across central Africa and the Caribbean) (a wet, fresh northerly wind across west central Africa) (northeasterly wind across the Philippines) (a violent wind on Cuba's southern coast) (northeasterly from eastern Europe to Italy) (warm dry westerly off the Rocky Mountains) (northerly across Greece and Turkey) (warm dry southerly off the northern side of the Alps and the North Italy) (afternoon sea breeze from the Indian Ocean which cools Perth during summer) (south wind in the Absheron Peninsula) (northeasterly from Greece) (southwesterly wind across the Philippines) (dry northerly wind across central Africa) (in northern Carpathians) (southeasterly from north Africa to the eastern Mediterranean) (cold north wind in the Absheron Peninsula) (strong and cold southeasterly season wind in Serbia) (easterly through Strait of Gibraltar) (southwesterly towards Italy) (south-easterly from Mediterranean to France) (cold northerly from central France and the Alps to Mediterranean) (eastern United States) (Brings rain to the West New Zealand, and warm dry winds to the East New Zealand) (southern California) (strong, dry, desert wind that blows in the Sahara, Palestine, Jordan, Syria, and Arabia) (southerly from north Africa to southern Europe) (rapidly arriving low pressure cell that dramatically cools Sydney during summer) (cold northwesterly from Pyrenees or northeasterly from Alps to the Mediterranean) (westerly through Strait of Gibraltar) (on the eastern slope of the Andes in Argentina)

Annexure 5: Meteorological instruments to measure wind speed and/or direction Anemometer (measures wind speed, either directly, e.g. with rotating cups, or indirectly, e.g. via pressure differences or the propagation speed of ultrasound signals) Rawinsonde (GPS-based wind measurement is performed by the probe) Weather balloon (passive measurement, balloon position is tracked from the ground visually or via radar; wind profile is computed from drift rate and the theoretical speed of ascent) Weather vane (used to indicate wind direction) Windsock (primarily used to indicate wind direction, may also be used to estimate wind speed by its angle)

Sandip Patil

Department of Landscape Architecture, CEPT University

LA - 9106

Geology & Geomorphology

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26

Annexure 6: World’s Highest Dunes

Dune

Height from Base (meters)

Notes Highest in Africa

383

Star Dune

230

2,730

Dune of Pilat Mount Tempest

105

130

Bay of Arcachon, Aquitaine, France

280

280

Moreton Bay, Brisbane, Australia

Highest in North America Highest in Europe Highest in Australia

500

2,020

Badain Jaran Desert, Alashan Plain, Inner Mongolia, Gobi Desert, China

World's Tallest Dunes?

Sandip Patil

~1,980

Location Isaouane-n-Tifernine Sand Sea, Algerian Sahara Sossuvlei Dunes, Namib Desert, Namibia Great Sand Dunes National Park, Colorado, USA

Highest Dune Big Daddy/ Dune 7

Badain Jaran Dunes

465

Height from Sea Level (meters)

Department of Landscape Architecture, CEPT University

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Bibliography Book References: • Tarbuck J., Earth Science, • Wonders of the World, Reader’s Digest • Duff, Holmes’ Principles of Geology, • Strange Worlds, Amazing Places • Wildlife Cards • Gaia Atlas of Planet Management Media References: • Director, Funny People, movie based on animal studies in the Kalahari Desert CEPT University Seminar Reports: • Verma Praveen K., Deserts: Geology & Resources, (unpublished) • Bade Kanchan, Wind Action & Desert Landscape, (unpublished) • Prabhu M., Wind Actions & Related Forms, (unpublished) • Puri, Anuradha, Deserts: Changing Landscapes sandblasted by winds, (unpublished) • Gulawani Ameeta, and others, Wind Erosion & Desert Landscapes, (unpublished) Internet References: • www.atlas.aaas.org • www.caltech.edu • www.tec.army.mil • www.usgs.gov • www.wikipedia.com ƒ

Sandip Patil

Atlas of Population and Environment, American Association of Adavancement of Science Caltech Desert processes working group, Knowledge Sciences Inc. United States Geological Service, publications Free online encyclopaedia Articles on Wikipedia are contributed by various users, and contain references from internet, published and unpublished sources. Acknowledgement is made for the same.

Department of Landscape Architecture, CEPT University

LA - 9106