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Physical Geography > Deserts > Flashcards

Deserts Flashcards

1
Q

Insolation

A

Energy from sunlight

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2
Q

Diurnal range

A

Maximum temperature - minimum temperature over a 24 hour period

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3
Q

Salinisation

A

Salt in water means that when evaporation occurs and water is brought up through the soil a salty crust is left on the surface

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4
Q

How much rainfall does an area need to have to be classified as a desert?

A

less than 250 mm

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5
Q

Desert Soil characteristics

A

Dry
Sandy
Red due to oxidation
Lack of vegetation

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6
Q

Ephemeral plants

A

Seasonal plants with very short life cycles
Stay dormant until conditions are correct to support life
e.g. Arabidopsis thaliana

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7
Q

Xerophytes

A

Plants that have fully adapted to living in desert conditions
They have spines instead of leaves in order to soak up available water quickly
Thick expandable stems for water storage
Waxy skin which reduces water loss
Water storage cells within the stem of the plant
e.g. cacti

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8
Q

Halophytes

A

Plants that have adapted to living in saline conditions
These plants have deep root systems
They shed leaves during the dry season to decrease water that is required
Have small leaves which reduce transpiration water loss and the surface area of the plant being exposed to the sun
e.g. salt bushes

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9
Q

Parasitic plants

A

Plants that obtain all or part of their nutrition from another plant without contributing to the benefit of the host

They have small leaves to reduce water loss
Stems store water
Waxy surface to reduce water loss
e.g. desert mistletoe

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10
Q

Causes of deserts

A

Global atmospheric circulation
Continentality
Rain shadow effect
Cold ocean currents

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11
Q

How does global atmospheric circulation cause deserts to form?

A

Air rises at the equator, expands and cools

The air beneath this in contact with the earth heats and rises, expands and cools

This cycle repeats

This rising air moves away from the equator via the hadley cell

When this air reaches 30 degrees north and south of the equator the air has cooled and descends due to having a low density

As it reaches earth it warms up slightly again and expands

Due to this there is little cloud cover and an area of low pressure is created alongside a desert

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12
Q

How does continentality cause deserts to form ?

A

Winds bring moisture picked up from oceans

As this wind travels over continents and land masses it loses moisture

This means that in the center of large land masses deserts form

(further from coast = dryer)

e.g parts of Sahara desert

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13
Q

How does the rain shadow effect cause deserts to form?

A

Moist air from the sea rises up mountains

This air cools, condenses and forms rain or snow

Precipitation falls on the windward side of the mountain

Air passes over the mountain range and flows downhill with little moisture

The land behind the mountain is considered to be in the rain shadow and commonly forms deserts

e.g. Atacama desert

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14
Q

How do cold ocean current cause deserts to form?

A

Air above the current is cooled

Mist and fog forms

Cool moist air moves towards the coastline

When it meets the land it meets warmer air

This inhibits cloud formation and leads to low levels of precipitation and causing aridity

e.g. Atacama

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15
Q

Landscape

A

includes elements of geophysically defined landforms such as mountains, hills, vegetation and human elements

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16
Q

Landform

A

features on the earths surface that make up the terrain and landscape

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17
Q

Weathering

A

the breakdown of rock in situ

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18
Q

Mechanical Weathering

A

The granular disintegration of rocks without any chemical change taking place

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19
Q

Types of mechanical weathering

A

Granular disintegration
Block separation
Shattering
Exfoliation

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20
Q

Granular disintegration

A

Coloured minerals in rocks such as granite are heated up at different rates which breaks up the rocks

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21
Q

Block seperation

A

If rocks have clear patterns of joins whole blocks can break apart

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22
Q

Shattering

A

Rocks without joins or grains shatter to form angular fragments due to heat

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23
Q

Exfoliation

A

rocks are poor conductors of heat meaning that the outer surface of the rock continuously cools and heats. This results in the outer layer of the rock flaking away.

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24
Q

Thermal fracture

A

Intense temperature fluctuations cause rocks to expand when heated and contract when cooled
Very dependent on colour, lithology and geological structure of the rock

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25
Q

Chemical weathering

A

The processes leading to the break down of rocks due to chemical reactions
Mostly requires water or exposure to air

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26
Q

Types of chemical weathering

A

Solution
Crystal growth
Hydration

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27
Q

Solution - rock

A

Rocks containing salts are vulnerable to being dissolved
Once dissolved high rates of evaporation lead to salt deposition

28
Q

Crystal Growth

A

Occurs after the process of solution

Deposition of salts leads to growth of crystals which are capable of corroding buildings and metal structures

29
Q

Hydration

A

Occurs when rocks absorb water and begin to swell which increases pressure inside the rock an dweakens it

30
Q

Erosion

A

Weathering down and removal of material / sediment

31
Q

Types of aeolian erosion

A

Deflation
Abrasion

32
Q

Deflation

A

Small light particles are carried by the wind leaving heavy, larger rocks and sediment behind
Desert pavement is created with the rocks left behind

33
Q

Abrasion

A

Known as the ‘ sandpaper effect ‘
Sand hits the rock surface carving them into a variety of shapes
Extent of the impact depends on the strength, duration and direction of the wind, the type of rock and the rock type of the sand being carried

34
Q

Types of transport

A

Suspension
Saltation
Surface creep

35
Q

Suspension

A

Wind carries light sediment

36
Q

Saltation

A

Larger sediment bounces along the ground at a max height of 1.5m

37
Q

Surface creep

A

Large rocks roll / get pushed along the surface by wind

38
Q

Deposition

A

Occurs when wind loses energy
Commonly occurs behind rocks as they intercept the wind and cause velocity to decrease

39
Q

Aeolian landforms

A

Deflation hollows
Desert pavements
Yardangs
Ventifacts
Zeugens
Barchans
Seif dunes

40
Q

Deflation hollows

A

Depression created by strong gusty winds that erode loose material from the desert surface within a flat landscape
processes = saltation, suspension, deflation

41
Q

Desert pavements

A

Surface covered with rock fragments when rock blow away finer rock and sand leaving behind larger stones
processes = deflation, suspension

42
Q

Yardangs

A

Elongated ridges seperated by deep grooves cut into the desert surface

Weaker rocks are eroded by abrasion to form deep troughs whilst the more resistant rock forms the yardangs

43
Q

Ventifacts

A

Individual rocks commonly found on desert pavements that have at least one clearly eroded face that is aligned with prevailing wind

44
Q

Zeugens

A

Similar to yardangs but develop horizontally giving a pedestal like shape and flat top which protects the layer of less resistant rocks

45
Q

Barchans

A

Crescent shaped sand dunes found in isolation where there is a limited supply of sand and a dominant wind direction

Sand is blown up the windward side before sliding down the steeper sheltered side

46
Q

Sief dunes

A

Elongated sand dunes commonly found in desert seas
They can stretch for several hundred meters and they form parallel to wind direction
A barchan develops first and as wind changes direction one horn is lengthened and becomes a seif dune

47
Q

Exogenous river

A

Rivers that have their source outside the desert region
e.g. Nile, Colorado

48
Q

Endoreic river

A

Rivers that flow into deserts and terminate in a lake or inland sea
e.g. River Jordan

49
Q

Ephemeral river

A

Rivers that flow seasonally in desert regions and are very likely to cause flash floods
e.g. River Ugab

50
Q

Episodic flash floods

A

Infrequent rainfall events that tend to involve convection rainfall and storms meaning large volumes of water in short amount of time

51
Q

Sheet flooding

A

When water flows as a sheet across the landscape and washing away loose soil particles

52
Q

Channel flooding

A

When water is confined to a channel

53
Q

Hydraulic action

A

Sheer force of water

54
Q

Corrasion

A

Fragments of rock carried by water hit bedrock

55
Q

Solution - water

A

Dissolving of soluble rocks

56
Q

Splash erosion

A

Force of falling rainwater displacing soil particles

57
Q

Rill erosion

A

Water wears down the soil to form a definite path and forming rills

58
Q

Gully erosion

A

When the rills widen and become gullies

59
Q

Bank erosion

A

Fast water flow wears away stream sides which causes the banks to collapse and the channel to widen

60
Q

Fluvial landforms

A

Wadis
Alluvial Fans and Bajada
Pediments
Inselbergs
Playas

61
Q

Wadis

A

Dry riverbed that can take the form of a distinct channel in a lowland plain or an incised gully or valley
Have steep sides due to severe erosion and flat bottoms with sediment

62
Q

Alluvial fans and bajada

A

Collection of sediment washed out through a wadi or canyon
Sediment is deposited quickly as the river spreads from the wadi and energy is lost

63
Q

Pedmients

A

Gently sloping erosional rock surface at the foot of a mountain range which has a distinct break of slope between the mountain front and the top of the pediment

64
Q

Inselbergs

A

Thought to have been formed in past pluvial climates with high humidity levels leading to chemical weathering of exposed rocks

65
Q

Playas

A

When water flows over pediments and deposits fine material onto the desert floor
Some water will percolate through this sediment and is collected in a hollow or depression
This large surface area encourages evaporation and a salty crust and playas form

66
Q

Orbital change (natural climate change)

A

The earths orbit is an ellipse that changes every 100,000 years

This means that the distance between the earth and the sun changes meaning temperature on earth changes as well

The axis of the earth is also on a tilt which changes every 41,000 years due to the gravitational pull of the moon

When the angle of the tilt increases the climate is exaggerated

67
Q

Desertification

A

The destruction of the biological potential of the land which can lead to desert like conditions

Physical Geography (3 decks)

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