Key Terms Flashcards
Potential evapotranspiration
is the maximum amount of evaporation and transpiration which could occur if water supply was unlimited.
Solar radiation
radiation emitted from the sun
Conduction
transfer of heat loss r gain through direct contact
Convection
transfer of heat through convective movement of air
Terrestrial radiation
radiation emitted from the earth
Albedo
the percentage of solar radiation reflected, as opposed to absorbed, by the earths surface
Trade Winds
surface prevailing winds which blow fro subtropical high pressure cell towards the Equator.
Advection fog
fog created when warm moist air comes into contact with a cold surface
Inversion layer
air layer where temperature rises rather than falls with height
Inter-tropical convergence zone
an area of rising air, low pressure, converging surface Trade Winds and high temperatures coincident with the Equator.
Coriolis
deflection of global winds by the rotation of the earth
Polar front
boundary about 50 degrees N and S of the Equator where cool air from the poles meets warm air form the subtropical high pressure cells producing rain.
Alveoles
small hollows, 5 - 50 cm in size, occurring in clusters or honeycombs with thin partitions strengthened b case hardening.
Tafoni
hollows a few metres across with arch shaped entrances, often developed along lines of weaknesses such as joints and bedding planes.
Case hardening
a hard layer of salt encrusted rock formed where salts have been drawn to the surface by capillary action
pedestal rock
isolated pillar of rock with an indented profile
Inselbergs
upstanding masses of crystalline rock that project above plains in deserts and semi-arid areas
Hydrolysis
a weathering process where water reacts with minerals such as feldspars to produce clay minerals
Deflation
the entrainment and removal by wind of unconsolidated material.
Corrasion
when wind-blown sand abrades rock surfaces
Deflation hollows
large enclosed depressions partly created by deflation; for example, the Qattara Depression in the Sahara
Salt pan
flat areas encrusted with salt sometimes filled with shallow, saline lakes
Desert pavement
surface of stones resting on a finer material such as sand, silt or clay. Known as gibber plains in Australia, and stone pavements in USA. Formed where wind or water selectively removes finer material to leave behind larger stones. Alternative theories suggest that coarse material is brought to the surface by cycles of heating and cooling, freezing and thawing, and wetting and drying.
Ventifact
wind polished stones which look like brazil nuts and are a few centimeters in size
Yardang
linear ridge of clay, silt or rock sculpted by abrasion and deflation
Zeugen
a type of pedestal rock with a resistant cap of rock
Suspension
fine sediment carried within the air
Saltation
movement of sand grains in a series of hops along the ground
Surface creep
rolling or pushing of sediment along the gorund
Sand sea
extensive area of sand containing a variety of dune types
Sand dune
Mound of loose, sand-sized material created by grain on grain movement.
Sand sheet
Extensive flat or gently undulating area of sand with no significant dunes and sparse vegetation.
Ephemeral river
Temporary river which flows intermittently or seasonally.
Braiding
The tendency for a river to spit into smaller channels and deposit material when attempting to carry a heavy load.
Exogenous river
A permanent river which drives its water from beyond the desert margin.
Pediment
Gently sloping bedrock surface extending from a mountain front to the alluvial plain below. Origin controversial, could be formed by wind or water erosion.
Ecosystems
Groups of organisms (plants, animals and bacteria) which interact with one another and the environment so that material is exchanged between the living and non-living (air, soil, water) parts of the system.
Ephemerals
Plants with a short life cycle which flower after rain and then seed and die.
Succulents
Plants which store water in fleshy stems and leaves.
Transpiration
Loss of water vapour to the atmosphere mainly via plant stomata.
Stomata
Pores in leaves and sometimes stems from which vapour escapes and through which oxygen and carbon dioxide is exchanged.
Cuticle
Waxy layer covering the outer plant wall designed to reduce water loss.
Xerophyte
Pants living in dry areas which have special mechanisms to survive drought such as swollen stems, thick cuticles, sunken and sometimes closed stomata, small leaves and spines. They include cacti and shrubs such as the creosote bush.
CAM (crassulacean acid metabolism)
A process by which carbon dioxide taken in at night is stored until the day when photosynthesis can occur without the plant opening the stomata.
Phreatophytes
Plants living in dry areas who have root systems to groundwater supplies.
Halophyte
Plant adapted to growing in saline conditions such as salt marshes and salt pans.
Cyptobiotic soil crust
Grey-brown soil crust composed of cyanobacteria, lichen moss and micro fungi. Filaments of cyanobacteria bind soil particles.
Nomadism
A wandering form if existence in search of good pasture and water for livestock and the collection of fruit and roots.
Hydroponics
The growing of crops without soil.
Sahel
A semi-arid area in the sub-Saharan Africa stretching from Senegal to Ethiopia where rainfall is unreliable and droughts occur.
Desertification
The conversion or marginal land to a desert brought about by naturally occurring periods of drought together with human mismanagement of land.
Salinisation
The accumulation of salt in the soil.
