deserts

Question 1

what is a desert

Answer 1

a great deficit of moisture with low rainfall and high evaporation. less than 250mm annual
determines characteristics of soil, vegetation, weathering, landforms and life

Question 2

why do deserts occur on the centre or west coasts of continents between 15 and 30 degrees north and south of the equator

Answer 2

at 30 north and south of equator, air descends and is compressed and warmed producing an area of high pressure. As air warms it hold more water vapour causing lower atmosphere to become dry. Low relative humidity with little water for surface evaporation gives clear skies
second is the rainshadow effect where mountain ranges act as a barrier preventing moisture from trade winds reaching opposite sides of continent
3rd is the presence of cold ocean waters on the western coasts.

Question 3

3 dominant types of features of deserts

Answer 3

• Hamada: bare rock deserts
• Erg: large areas of dunes (25% of earths deserts)
• Desert pavements: form through the gradual removal of sand, dust and other fine-grained material by the wind and intermittent rain, leaving the larger fragments behind.

Question 4

Duricrusts?

Answer 4

Hard surface crusts classified by concentration of minerals

can help reduce erosion rates

Question 5

describe the 4 types of duricrusts

Answer 5

-Silcrete
rich in silica, hard and chemically stable, erosion resistant
- Calcrete CaCO3
widespread distribution
- Gypsum CaSO4.H20
most soluble, more than 250mm annual precipitation
-Ferricrete
iron rich, physically and chemically durable

Question 6

explain transport mechanisms

Answer 6

• Suspension
  very fine material raised high, can create dust storms
• Saltation
  fine and coarse particles lifted and moved
  usually around 2m high lift
• Surface Creep
  small stones and pebbles are moved by contact with smaller particles in motion from saltation

Question 7

explain 2 dominant mechanisms of erosion

Answer 7

Deflation: progressive removal of fine material by the wind leaving larger material behind
Abrasion: sandblasting action effected by materials moved by saltation, smoothens and polishes material
produces ventifacts, yardangs, and zeugens

Question 8

yardangs, ventifacts and zeugen?

Answer 8

ventifacts are individual rocks with sharp edges and smooth sides
yardangs are extensive ridges of rock seperated by troughs, aligned similar to that of the wind
zeugen tabular masses of resistant rock seperated by vertically cut trenches

Question 9

exogenous, endoreic and ephemeral rivers

Answer 9

exogenous - sources lie outside the arid zones, and are vital for sustaining life
endoreic - occurs where rivers terminate in inland lakes because of altitude below sea level
ephemeral - flows intermittently after storms, are dangerous because of presence of impermeable rock and lack of vegetation

Question 10

pediment

Answer 10

gentle sloping area of rock before highlands, formed by deposition of sediment from pluvial periods

Question 11

playas

Answer 11

shallow, ephemeral lakes formed after storms, found at lowest part of pediment