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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
Chemical weathering
The processes leading to the break down of rocks due to chemical reactions Mostly requires water or exposure to air
26
Types of chemical weathering
Solution Crystal growth Hydration
27
Solution - rock
Rocks containing salts are vulnerable to being dissolved Once dissolved high rates of evaporation lead to salt deposition
28
Crystal Growth
Occurs after the process of solution Deposition of salts leads to growth of crystals which are capable of corroding buildings and metal structures
29
Hydration
Occurs when rocks absorb water and begin to swell which increases pressure inside the rock an dweakens it
30
Erosion
Weathering down and removal of material / sediment
31
Types of aeolian erosion
Deflation Abrasion
32
Deflation
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
Abrasion
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
Types of transport
Suspension Saltation Surface creep
35
Suspension
Wind carries light sediment
36
Saltation
Larger sediment bounces along the ground at a max height of 1.5m
37
Surface creep
Large rocks roll / get pushed along the surface by wind
38
Deposition
Occurs when wind loses energy Commonly occurs behind rocks as they intercept the wind and cause velocity to decrease
39
Aeolian landforms
Deflation hollows Desert pavements Yardangs Ventifacts Zeugens Barchans Seif dunes
40
Deflation hollows
Depression created by strong gusty winds that erode loose material from the desert surface within a flat landscape processes = saltation, suspension, deflation
41
Desert pavements
Surface covered with rock fragments when rock blow away finer rock and sand leaving behind larger stones processes = deflation, suspension
42
Yardangs
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
Ventifacts
Individual rocks commonly found on desert pavements that have at least one clearly eroded face that is aligned with prevailing wind
44
Zeugens
Similar to yardangs but develop horizontally giving a pedestal like shape and flat top which protects the layer of less resistant rocks
45
Barchans
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
Sief dunes
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
Exogenous river
Rivers that have their source outside the desert region e.g. Nile, Colorado
48
Endoreic river
Rivers that flow into deserts and terminate in a lake or inland sea e.g. River Jordan
49
Ephemeral river
Rivers that flow seasonally in desert regions and are very likely to cause flash floods e.g. River Ugab
50
Episodic flash floods
Infrequent rainfall events that tend to involve convection rainfall and storms meaning large volumes of water in short amount of time
51
Sheet flooding
When water flows as a sheet across the landscape and washing away loose soil particles
52
Channel flooding
When water is confined to a channel
53
Hydraulic action
Sheer force of water
54
Corrasion
Fragments of rock carried by water hit bedrock
55
Solution - water
Dissolving of soluble rocks
56
Splash erosion
Force of falling rainwater displacing soil particles
57
Rill erosion
Water wears down the soil to form a definite path and forming rills
58
Gully erosion
When the rills widen and become gullies
59
Bank erosion
Fast water flow wears away stream sides which causes the banks to collapse and the channel to widen
60
Fluvial landforms
Wadis Alluvial Fans and Bajada Pediments Inselbergs Playas
61
Wadis
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
Alluvial fans and bajada
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
Pedmients
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
Inselbergs
Thought to have been formed in past pluvial climates with high humidity levels leading to chemical weathering of exposed rocks
65
Playas
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
Orbital change (natural climate change)
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
Desertification
The destruction of the biological potential of the land which can lead to desert like conditions

Physical Geography (3 decks)

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