Hot Deserts

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105 Terms

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Desert
A large barren area with minimal precipitation and high temperatures. 1/5 of earth’s surface, often running in parallel belts either side of the equator in mid-low latitudes, mostly in the northern hemisphere to the west of continents
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Aridity Index
Ratio between precipitation and evapotranspiration
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Hyper-arid
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Arid
An area 100-250mm of rain, with a 0.05-0.20 aridity index 
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Semi-arid
250-500mm precipitation, 0.20-0.50 aridity index 
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Water balance
Precipitation = evaporation +/- soil water storage + runoff
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Continentality
The way a large land mass affects weather and climate, with air masses losing moisture as it travels inland, leading to less precipitation and vegetation
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Relief
Air descends on the leeward side of a slope, causing it to become warmer and drier
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Global oceanic circulation 
The large-scale movement of water, with warm water carried towards the poles, cooling and sinking, and eventually returning to the surface, carried back to the tropics 
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Inter-tropical convergence zone (ITCZ) 
A band of low pressure around the Earth which generally lies near to the equator
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Atmospheric processes
Air is heated at the equator, rising, cooling, condensing and eventually sinking, producing a high pressure air mass which warms due to compression as it descends This produces a stable air mass, creating an anticyclone
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Hadley Cell 
0-30° Beginning at the equator, where solar radiation warms the air causing it to rise through convection. This rising air causes low pressure at the surface
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Ferrell Cell 
30-60° latitude, with cold air sinking at 30 and rising at 60 
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Diurnal temperature range 
The difference between the hottest and coldest point over a 24-hour period: high due to little cloud cover
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Potential evapotranspiration (PET) 
The amount of water that would be evaporated if sufficient water is available 
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Humidity
How much water vapour is in an air particle 
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Soil profile
Vertical cross-section of the soil 
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Capillary movement
Water moving upwards through soil pores 
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Aridisols
Reddish-yellow to grey-brown in colour, thin
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Raw mineral soils
Coarse texture, rocky due to physical weathering. Calcium/sodium salts accumulate near the surface due to water existing, little leaching causes little variation between horizons. Slightly alkaline, unproductive
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Sierozem
Grey desert soils, developing below vegetation, calcium-rich horizons can develop below, with rich accumulations of calcium carbonate lightening the soil. Often used for cultivation
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Leaching
Removal of nutrients by water
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Xerophyte
Plants that have adapted to live in desert environments with thick, waxy cuticles, and small/spiky/no leaves reducing water loss
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Phreatophyte 
Plants with long roots to tap into the ground water 
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Halophyte
Plants adapted to saline soils
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Ephermals
Plants with short life cycles, appearing after storms and becoming dormant during dry spells
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Angle of incidence
The angle formed by a ray or wave on a surface and a line perpendicular to the surface at the point of incidence
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Insolation
The amount of short-wave radiation reaching the earth’s surface, some radiated back due to little cloud cover
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Rain shadow 
An area forced to become a desert due to mountain ranges blocking rain 
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Sediment
Small material usually consisting of sand  
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Sediment cell
The movement of sediment
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Sediment budget
Relative amount of sediment in each part of the system 
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Weathering
The breakdown or decay of rocks as a result of the weather 
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Thermal fracture
Weathering due to expansion and contraction of the outer surface of rocks due to intense temperatures 
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Exfoliation
The peeling/flaking of the outer skin of the rocks due to intense hot and cold temperatures
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Chemical weathering
Absorption of carbon dioxide in the atmosphere, breaking down rocks
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Mass movement
The movement of a large amount of material downwards due to gravity 
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Erosion
The wearing away of material
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Denudation
Wearing away of the surface by weathering and erosion
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Rill erosion
Sheet wash forming a path
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Sheet erosion
Water flowing as a sheet, washing away particles
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Gully erosion
Rills becoming wider and deeper
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Splash erosion
The force of rainwater displacing soil particles
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Bank erosion
Fast water wearing away the sides of streams
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Hydraulic action
The force of water into cracks of rock
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Abrasion
Transported material hits exposed surfaces, carving and sculpting it, affected by the particle size/nature, the lithology of the ground and the directon/frequency/velocity of the wind
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Corrosion
Fragments of rock carried by water
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Solution
The dissolving of soluble rocks
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Wind
Driven by atmospheric circulation, seasonal or trade winds. Caused by: air is heated, rises and cooler air moves to replace, high angle of incidence, limited cloud cover and vegetation
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Traction
The rolling of sediment over the surface
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Saltation
Sand-sized particles bounce along the surface
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Suspension
Fine particles held in the air
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Deposition
When waves run out of energy to carry and transport sediment
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Hydration
The process of absorbing water
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Hydrolysis
The chemical breakdown due to a reaction with water
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Oxidation
The addition of oxygen
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Crust
Thin layer of material on top of soil 
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Duricrust or hardpan 
A mineral crust formed on the surface of soil due to evaporation of groundwater
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Desert varnish
A dark coating found on rocks exposed to the sun
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Block/granular disintegration
The breaking down of rocks made of grains into sand grains 
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Loess
A wind deposit of silty material, usually yellow to brown in colour 
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Deflation
Wind erosion involving the removal of loose material from the desert floor, exposing underlying bedrock 
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Surface creep
Accounts for 25% of movement: particles hit larger ones, causing them to slide/roll along the surface, in conjunction with saltation
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Exogenous rivers
Originating outside the desert
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Endoreic rivers
Rivers that never reach the sea, draining into an inland sea instead
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Ephemeral rivers
Rivers that only flow seasonally, after a heavy rainfall event
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Distributaries
River channels branching away from the main river channel 
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Episodic flash floods
Infrequent rainfall events, causing intense surface runoff
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Sheet flooding
Flooding after a storm where water flows in sheets across a landscape rather than going into gullies and valleys 
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Channel flash flooding
Flooding that happens after a storm where water makes it way into channels
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Deflation hollows
A depression caused by wind eroding loose material from the surface 
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Reg/desert pavement
A stony desert area where rock fragments are scattered over a large plain 
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Venifacts
Sharply angled rock found on a desert pavement formed by abrasion 
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Yardang
A streamlined rock structure formed where horizontally laid rocks form elongated ridges, separated by deep grooves cut into the surface. Weaker rock is eroded by abrasion to form deep troughs, with tougher rock left upstanding
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Zeugen
Ridge formed by abrasion of vertical bands of resistant rock
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Barchan
Crescent-shaped sand dunes formed at right angles to the prevailing winds 
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Sief dunes
Linear sand dune formed parallel to prevailing winds 
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Wadis
Dry river channel formed by periodic water erosion 
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Pediments
Gently sloping, usually concave rocks surface at the foot of a mountain front
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Alluvial fan - Lucy Gray Fan
Washed out sediment is deposited, displaying stratification with finer sediment washed out onto the desert plain
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Bajada
Extensive alluvial fans can coalesce to form a continuous apron of sediment
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Playa - soda lake
Water carried onto the desert floor percolates through loose sediment, transferring as throughflow to collect in large hollows/depressions
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Inselbergs
Develop from rocks which eroding at a slower rate than surrounding rocks, consisting of erosion-resistant rock protecting the softer rock
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Scree
Small loose stones forming over a slope 
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Mesa
Table-like relic landform formed in horizontally bedded rocks 
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Butte
Smaller pinnacles of rock surrounded by flat desert plains 
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Badlands
Clay-rich soil, extensively eroded  
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Plateaux
A flat, elevated landform rising sharply above the surrounding area on one side 
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Gullies
A trench in land due to eroded water, created an accelerated stream
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Interglacial
A warm period between glacial eras
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Oasis
An area made fertile due to freshwater in an otherwise dry area
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Desertification
Turning marginal land into desert by destroying the biodiversity potential
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Ecosystems
A geographic area where a range of organisms depend on each other for life 
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Human Development Index (HDI) 
A mix of indices that show life expectancy, knowledge (adult literacy and education) and standard of living (GDP per capita) measuring development 
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Grassroots 
Using the people in a given area as the basis for a larger political or economic movement 
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Regionalisation 
Dividing an area into smaller segments, adapting to fit a smaller area 
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Globalisation 
The increased connections between places and people over the world 
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Landsat 
A satellite studying and photographing the earth's surface using remote-sensing techniques
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Mitigate 
Reduce or prevent the effects of something 
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Sustainable Solutions 
Allowing something to continue without harming the future generation’s resources