Systems And Processes In Hot Deserts

Question 1

What is abrasion?

Answer 1

Where material carried by moving wind or water hits exposed rock surfaces, thus wearing them away. Often referred to as sandblasting or sandpapering effect.

Question 2

Define aeolian?

Answer 2

Relating to the action of the wind

Question 3

Define chemical weathering ?

Answer 3

The process leading to decomposition or breaking down of rocks due to chemical reactions. This most often requires the presence of water, and/ or exposure to the air.

Question 4

Define deflation?

Answer 4

Where wind removes dry, unconsolidated (loose sand), silly and clay particles from the surface and transports them away.

Question 5

Define deposition ?

Answer 5

Occurs when the velocity of the wind decreases until it can no longer transport the grains it is carrying.

Question 6

Define endoreic streams ?

Answer 6

Where rivers occupy drainage basins that are closed and do not flow out to the sea or other rivers, but instead end inland in lakes or swamps

Question 7

Define ephemeral streams?

Answer 7

Streams that flow intermittently in hot desert areas following heavy thunderstorms

Question 8

Define exfoliation ?

Answer 8

A process of mechanical weathering that results in the breaking, splitting or peeling off of the outer rock layer. Also commonly known as onion skin weathering.

Question 9

What are exogenous streams?

Answer 9

Rivers that originate external to the desert in adjacent highlands and more humid environments, flow from outside of the desert and pass through it.

Question 10

Define insolation?

Answer 10

The incoming solar radiation that reaches the earths surface

Question 11

Define mass movement

Answer 11

The movement of material downhill under the influence of gravity, but may also be assisted by rainfall

Question 12

Define saltation

Answer 12

A process where sand sized particles are transported by bouncing and hopping along the surface

Question 13

Define sediment

Answer 13

Any naturally occour in material that has been broken down by the processes of erosion and weathering and has then been transported and subsequently deposited by the action of ice, wind or water

Question 14

Define sediment budget

Answer 14

The balance between inputs and output of sediment in the hot deserts

Question 15

Define surface creep

Answer 15

Where saltating particles return to the surface and hit larger particles that are too heavy to hop; they slowly creep (slide or roll) along the surface from a combination of the push of the saltating grain and the movement of the wind

Question 16

Define transportation

Answer 16

Transportation is the process that move material from the site where erosion took place to the site of deposition

Question 17

Define suspension

Answer 17

Transportation by wind where the smallest particles, generally less than 0.2millimetres, are held in the air

Question 18

Define thermal fracture

Answer 18

The weathering of rock resulting from its rapid and repeated heating and cooling

Question 19

Define weathering

Answer 19

The breakdown and/or decay of rock at or near the earths surface creating regolith that remains in situ until it is moved by later erosional processes. Weathering can be mechanical, biological/organic or chemical.

Question 20

Explain the relative importance of 3 different sources of energy in hot desert environments?

Answer 20

(Relative importance should consider frequency, intensity, how much impact)

1. Insolation
   -incoming solar radiation from the sun
   - at desert latitudes the sounds rays are at a high angle of incidence
   - this means the heat is concentrated on a very small area (high intensity)
   - in the desert there is little moisture so limited evaporation, so little later heat is absorbed, so there is more heat in the atmosphere (relatively), which contributes to the intensity of thermal energy in hot deserts
   - VERY FREQUENT, HAPPENS DAILY 5 HOURS
   - causes weathering and evaporation which makes sediment more mobile
2. Winds
   -created by air moving from areas of high pressure to areas of low pressure (so they move from centre of deserts outwards)
   - eg, the harmattan winds blows across the Sahara in winter months from November to March
   - can be very strong if the pressure gradient is high (big difference between high and low pressures)
   - often very intense because of the lac of vegetation means wind can blow long distances without obstruction, increasing its power (less important in semi-arid deserts)
   - NOT AS FREQUENT AS INSOLATION
   - erode, transport and involved in deposition
3. Runoff
   - VERY INFREQUENT, Peru only receives an annual precipitation of 4mm, Chicama
   - water has a more important role in some deserts eg, El Djem, Tunisia which recieves 275mm annually
   - runoff is intense during storms because there is little vegetation to intercept the rainfall and in lots of areas the ground has been baked by the sun, reducing infiltration
   - transports and erodes

Question 21

Explain the concept of a sediment cell in a hot desert landscape

Answer 21

A sediment cell is a system within the larger desert system which looks at the movement of sediment within the desert. (Inputs, stores and outputs of sediment )

Question 22

What is a sediment budget?

Answer 22

The balance between the input and output of sediment in hot deserts.

Areas dominated by erosion are a source of sediment and the system has a net sediment loss

In those dominated by transportation and deposition of sediment, the system has a net sediment gain.

Question 23

What are the sources / inputs of sediment?

Answer 23

Sediment may simply be derived from the weathering of the underlying parent rock

Sediment may be fluvial in origin, rivers may bring the sediment into deserts

Other sediments originating beyond desert margins may be aeolian and be transported in and deposited by wind as loess.

Question 24

Explain the 5 groups if geomorphological process in hot deserts ?

Answer 24

1. Weathering
   - breaking down or decay of material where it is
   - does not involve transportation, instead produces material known as regolith
   - different types - chemical and mechanical weathering
2. Mass movement
   - movement of material under the influence of gravity but may be also be assisted by rainfall
   - rock falls (small blocks of rocks become detached and fall freely) and rock slides (failure throughout the rock as a whole and the materials collapses )
3. Erosion
   - refers to the process tat wears away the land by mechanical action (eg, water and wind)
4. Transport
   - refers to the process that moves material from where erosion took place to the site of deposition
   - agents performing this is wind and water
5. Deposition
   - occurs when the velocity of the wind decreases until it no longer transports the material it is carrying.
   - as moving wind and water are not continuous present in deserts environments deposition features are common.
   - a common cause in evaporation, leaving the load behind