Final Study Guide 12 Flashcards
Deserts and Desertification
What is desertification?
- The process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture. Such as sand dunes moving often and desert taking over. Increase in temperature and change in wind pattern drive desertification.
- Desertification is the expansion of desert areas (deserts: Deserts are, according to some climatologist, a “dry” region, i.e one in which yearly rainfall is less than the potential evaporation rate in that region).
- Process governed by:
> how close to certain temp range likely for turning land into a desert
> type of vegetation→ taking away vegetation in which roots normally stabilize ground. No stabilization = deflation (easier to erode the ground material)
What determines the geographic location of deserts?
Mainly things such as rain fall amount, wind/atmospheric circulation, temperature, climate, and orographics (rain shadow effect)
What are the possible impacts of sandstorms, locally and globally?
- Sand storms interrupt air/ground traffic, create big wind/season climate variations, destroy vegetation, low visibility and diseases.
- Carry sand to different places locally and even across oceans to help enrich soils and sustain beaches.
- The sand from these storms stays in the atmosphere and is dangerous because it settles at the deepest part of your lungs
- Seasonal climate variation
- Drastic changes in weather and climate due to changes in albedo
- Air pollution is enhanced by sandstorms
> Beijing and Gobi Desert
Desert
- “dry” regions in which yearly rainfall is less than the potential evaporation rate in that region
> features: topography, latitude, away from oceans, human impact
> Develop because of: atmospheric circulation, location within continental interiors, or orographic (rain shadow) deserts.
Sandy desert
Ex: Great Sandy Desert, Australia
Rocky desert
- Ex: Mojave in CA
- Cacti
Devil’s racetrack
huge boulders that leave a track on the surface of a dried lake bed
Sandstorms
- Jets of sand being transported by wind
- Seasonal
- Interrupt air traffic
- Enhance air pollution
Particulate smog
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Precipitation
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Evaporation
The change of state from a liquid to a gas form. This typically happens with liquids that come in contact with energy or heat and rise into the air as vapor
Low Latitude Desert
- closer to the equator where the sun is hotter and heats sand more
- Hot sand heats air→air rises→prevents cool, moisture filled air from lowering and prevents precipitation
Orographic desert
- Desert caused by a rain shadow
- Receive little moisture due to rain shadow
Rain Shadow
- dry area on the side of a mountain away from the wind
- Mountains block the passage of rain-producing weather systems and cast a dry shadow
Kalahari
Large, semi-arid, sandy desert in southern Africa
Sahara
- World’s hottest desert and third largest
- Huge sand dunes
Gobi
- a type of desert, the advance of Gobi Desert Dunes in China
- Rock floor desert plain
Trade winds
- Prevailing pattern of easterly surface winds found in the tropics (near the equation), within the lower portion of earth’s atmosphere
- Blow from northeast in the northern hemisphere and from the southeast in the southern hemisphere
- East→West
Westerlies
- Prevailing pattern of winds in middle latitude between 30-60 degrees
- Blows West→East
- Affects ocean currents
Taklamakan
- Desert in China
- Shifting sand desert with lots of dunes
- Lies in rain shadow of Himalayas→cold desert climate
Sierra Nevada
- Snowy mountain range in CA and NV
- Casts a rain shadow into the Great Basin
Vulnerability
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Desertification
The process by which fertile land becomes desert
Wind erosion
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Settling velocity
the faster settling velocity = thicker particles
Turbulence
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Wind shadow
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Dune formation
- Dunes can form in different ways, but often from saltation
- Saltation: particle transport by wind or water
Vortex
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Stream lines
direction of wind movement
Slip face
Also known as “Lee face” , side of mountain that does not get wind
Deposition
the laying down of sediment carried by wind, water, or ice. Sediment can be transported as pebbles, sand & mud, or as salts dissolved in water. Salts may later be deposited by organic activity (e.g. as sea-shells) or by evaporation
Critical angle
34 degrees
Sand stone
- clastic sedimentary rock composed mainly of sand-sized minerals or rock grains
- Rock formations of sandstone are porous enough to store large quantities of liquids–good aquifers as they also filter out pollutants
Barchan
Crescent shaped dunes with horns pointing downwind
Transverse dune
Linear dune that moves perpendicular to the wind
Longitudinal Dune
Linear dune that moves parallel to the wind
Avalanche
rapid flow of snow down a sloping surface
Desert Pavement
- packed surface coating of rocks, usually above a layer of windblown dust
- Two proposed ways:
> Deflation→remove finer particle→desert pavement established→deflation ends
> Weathered pebbles on bedrock→wind-blown silt accumulated and sifts downward through coarse particles→silt continues to accumulate→makes desert pavement
Desert varnish
- A layer of minerals formed over long times, by means of chemical interactions between the rock and the little humidity you find in deserts
- Very slow process; 1mm can take up to 1,000 years
Deflation
- Wind or water picks up and carries small particles
- Three types:
> Surface Creep: larger, heavier particles, slide or roll across the ground
> Saltation: particles are lifted a short height into the air, bounce, and transported
> Suspension: very small & light particles are lifted in the air and carried a long way by the wind
