Desert and Winds

Chapter 19 Deserts and Winds : 

Chapter 19 Deserts and Winds

Distribution and causes of dry lands : 

Distribution and causes of dry lands Dry regions cover 30 percent of Earth’s land surface Two climatic types are commonly recognized Desert or arid Steppe or semiarid

Desert and steppe regions of the world : 

Desert and steppe regions of the world Figure 19.2

Distribution and causes of dry lands : 

Distribution and causes of dry lands Dry lands are concentrated in two regions Subtropics Low-latitude deserts In the vicinities of the Tropics of Cancer and Capricorn Areas of high pressure and sinking air that is compressed and warmed

Subtropical high pressure belts and dry regions : 

Subtropical high pressure belts and dry regions Figure 19.3

Distribution and causes of dry lands : 

Distribution and causes of dry lands Dry lands are concentrated in two regions Middle-latitudes Located in the deep interiors of continents High mountains in the path of the prevailing winds produce a rainshadow desert

Rainshadow desert : 

Rainshadow desert Figure 19.4

Slide 8: 

Table 19.A

Geologic processes in arid climates : 

Geologic processes in arid climates Weathering Not as effective as in humid regions Mechanical weathering produces unaltered rock and mineral fragments Some chemical weathering in deserts does produce Clay Thin soils Oxidized minerals

Geologic processes in arid climates : 

Geologic processes in arid climates Role of water in arid climates Practically all streambeds are dry most of the time Desert stream are said to be ephemeral Carry water only during periods of rainfall Different names are used for desert streams in various region Wash and arroyo (western United States) Wadi (Arabia and North Africa)

Geologic processes in arid climates : 

Geologic processes in arid climates Role of water in arid climates Desert streams are said to be ephemeral Different names are used for desert streams in various regions Donga (South America) Nullah (India) Desert rainfall Rain often occurs as heavy showers

Geologic processes in arid climates : 

Geologic processes in arid climates Role of water in arid climates Desert rainfall Because desert vegetative cover is sparse, runoff is largely unhindered and flash floods are common Poorly integrated drainage systems and streams lack an extensive system of tributaries Most of the erosion work in a desert is done by running water

A dry channel contains water only following heavy rain : 

A dry channel contains water only following heavy rain Figure 19.5

Basin and Range: Evolution of a desert landscape : 

Basin and Range: Evolution of a desert landscape Characterized by interior drainage Landscape evolution in the Basin and Range region Uplift of mountains – block faulting Interior drainage into basins produces Alluvial fans Bajadas Playas and playa lakes

Basin and Range: Evolution of a desert landscape : 

Basin and Range: Evolution of a desert landscape Landscape evolution in the Basin and Range region Ongoing erosion of the mountain mass Produces sediment that fills the basin Diminishes local relief Produce isolated erosional remnants called inselbergs

Inselbergs in southern California : 

Inselbergs in southern California

Wind in the desert : 

Wind in the desert Transportation of sediment by wind Differs from that of running water in two ways Wind is less capable of picking up and transporting coarse materials Wind is not confined to channels and can spread sediment over large areas

Wind in the desert : 

Wind in the desert Transportation of sediment by wind Mechanisms of transport Bedload Saltation – skipping and bouncing along the surface About 20 to 25 percent of the sand transported in a sandstorm is moved this way Suspended load

Wind in the desert : 

Wind in the desert Wind erosion Wind is a relatively insignificant erosional agent with most erosion in a desert performed by intermittent running water Mechanisms of wind erosion Deflation Lifting of loose material Deflation produces blowouts (shallow depressions) and desert pavement (a surface of coarse pebbles and cobbles)

Formation of a desert blowout : 

Formation of a desert blowout Figure 19.12

Formation of desert pavement : 

Formation of desert pavement Figure 19.13

Wind in the desert : 

Wind in the desert Wind erosion Mechanisms of wind erosion Abrasion Produces ventifacts (stones with flat faces) and yardangs (wind sculpted ridges) Limited in vertical extent

Wind in the desert : 

Wind in the desert Wind deposits Significant depositional landforms are created by wind in some regions Two types of wind deposits Dunes Mounds or ridges of sand Often asymmetrically shaped Windward slope is gently inclined and the leeward slope is called the slip face

Formation of sand dunes : 

Formation of sand dunes Figure 19.13

Sand dunes in the western United States : 

Sand dunes in the western United States

Wind in the desert : 

Wind in the desert Wind deposits Two types of wind deposits Dunes Slow migration of dunes in the direction of wind movement Several types of sand dunes including barchan, transverse, longitudinal, parabolic and star dunes

Wind in the desert : 

Wind in the desert Wind deposits Two types of wind deposits Loess Blankets of windblown silt Two primary sources are deserts and glacial outwash deposits Extensive deposits occur in China and the central United States

End of Chapter 19 : 

End of Chapter 19