Y2) TERM 1- DESERTS Flashcards

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1
Q

Describe typical hot desert characteristics

A

Typical hot desert characteristics would include dry (less than 250mm precipitation per yea), large diurnal temperature range, little biomass, and hot! (20-30oC)

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2
Q

How does atmospheric circulation cause aridity?

A

Atmospheric circulation causes aridity as high pressure (dry and cloudless) is created at the tropics due to the falling limb of the Hadley and Ferrel cells (driven by convection at the equator)

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3
Q

How does continentality cause aridity?

A

Continentality causes aridity since moisture becomes less available with distance from a large body of water – the further inland you go, the drier it gets

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4
Q

How does relief/ orography cause aridity?

A

Relief/ orography causes aridity by forcing warm and moist air to rise, cool and condense, which forms clouds (which rains!) – the leeward side therefore receives no rainfall, and is likely to be arid

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5
Q

How do cold ocean currents cause aridity?

A

Cold ocean currents cause aridity by limiting the amount of evaporation that can occur (as air is cooled, thus unable to contain much moisture) – air may be foggy, but not really “wet”!

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6
Q

What is the aridity index?

A

The Aridity index is a measure of dryness, as a ratio on precipitation vs potential evapotranspiration; the lower the value, the drier a place is.

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7
Q

What is the aridity index?

A

The Aridity index is a measure of dryness, as a ratio on precipitation vs potential evapotranspiration; the lower the value, the drier a place is.

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8
Q

Describe the “Soil Moisture Budget”

A

The “Soil Moisture Budget” shows how soil moisture varies throughout a year, depending on the relationship between precipitation (input) and evapotranspiration (output)

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9
Q

What is “positive feedback”? (Can you think of an example in a desert setting?)

A

“Positive feedback” is a self-perpetuating/ self-reinforcing cycle, that spiral further away from equilibrium. E.g., a lack of vegetation = reduced evapotranspiration = reduced rainfall = reduced vegetation = reduced evapotranspiration….

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10
Q

What is “negative feedback”? (Can you think of an example in a desert setting?)

A

“Negative feedback” is where a “check” occurs (an event that stops everything spiralling out of control/ further from equilibrium) Example: weathering = build up of sediment at slope bases (called “scree”) = protection of the slope = reduced weathering

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11
Q

describe desert soils

A

Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface

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12
Q

Describe the soil moisture budget

A

The “Soil Moisture Budget” shows how soil moisture varies throughout a year, depending on the relationship between precipitation (input) and evapotranspiration (output)

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13
Q

Summerise typical desert soil characteristics

A

Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface

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14
Q

Describe typical desert vegetation

A

Typical desert vegetation is small, occurs in patches, huddles together in each others shade, may have long/wide roots, will be succulent, corrugated, hydronasty

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15
Q

What are the inputs into a desert system?

A

Desert inputs include: water, heat and sediment

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16
Q

Summarise typical desert soil characteristics

A

Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface

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17
Q

Describe typical desert vegetation

A

Typical desert vegetation is small, occurs in patches, huddles together in each other’s shade, may have long/ wide roots, be succulent, corrugated, hydronasty…

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18
Q

What is weathering?

A

Weathering is the process of breaking down a rock in situ (i.e. no movement); water and heat are very important (but deserts have very little water!)

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19
Q

List some examples of weathering…

A

Weathering types:
- Mechanical: Thermal fracture // Salt weathering // Frost shattering
- Chemical: Oxidation // Hydration // Carbonation
- Biological: Roots // Lichen

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20
Q

Abrasion…deflation… what’s the difference?

A

Abrasion is the “sand-blasting” effect of particles colliding with surfaces up to ~2m in height, gradually wearing it away; deflation is the ground surface gradually lowering as finer material is removed

21
Q

Saltation…suspension…traction… what’s the difference?

A

Saltation is where small particles “bounce” along, suspension is where smaller particles are “carried” along, and traction/ surface creep is where the heaviest material is dragged/ rolled along

22
Q

What are the 3 main types of river found in a desert?

A

The 3 main types of river found in a desert are exogenous, endoreic, ephemeral

23
Q

What is episodic rainfall?

A

sodic rainfall = occasional/ sporadic rainfall

24
Q

Water in the desert

A

Water in the desert – rare, but powerful

25
Q

Why is the Sahara Desert a desert?

A

The Sahara Desert is a desert due to atmospheric circulation (high pressure, falling limbs of Hadley and Ferrel cells), cold ocean current (Canary Current), possible relief in some places (Highlands), and central areas due to continentality

26
Q

What is desertification?

A

Desertification is “Land degradation in arid & semi-arid areas resulting from various factors including climatic variations and human activities”

27
Q

Why does climate change naturally?

A

Natural climate change: Milankovitch cycles // Plate tectonics (alter ocean currents and global heat distribution) // Volcanic eruptions (alter atmospheric composition) // Variations in sunspot activity/ solar flares // Changes in ice coverage, albedo and positive feedback mechanisms

28
Q

Why does climate change due to humans?

A

Human causes of climate change: Aka anthropogenic causes (enhanced greenhouse effect – fossil fuels/ deforestation/ concrete/ agriculture…)

29
Q

What impact are current climate trends likely to have on deserts?

A

Current climate trends are likely to lead to deserts becoming hotter and drier

30
Q

what desert landforms are Fluvial

A

Plateau
Mesa
Butte
Inselbergs
Pediments
Playas (aka salt pan)
Wadis
Canyon
Alluvial fans
Bahadas (bajadas)

31
Q

what desert landforms are Aeolian

A

Deflation hollow
Desert pavement
Yardang
Zeugen
Ventifact
Barchan dune
Seif dune

32
Q

Plateau

A

Large elevated flat areas

Colorado plateau - 2,000m asl

33
Q

Mesa

A

Fluvial

Erosion

Remnants of erosion of a mesa/ section of a plateau ,Wider than its taller

100,000+ years to form

34
Q

Butte

A

Fluvial

Erosion

Continues erosion of a mesa/ section of plateau , taller than it is wider

100,000 + years to form

35
Q

Inselbergs

A

Fluvial

Erosion

Differential erosion usually by water- hard rock remains , (lines of hard rock)

100,000 + years to form

36
Q

Pediments

A

Fluvial

Erosion

Sheet flooding at the mountain foot, abrasion, traction , saltation

100,000+ years

37
Q

Playas (aka salt pan)

A

Fluvial

Erosion

Deflation may become a temporary lake in times of rainfall, unless the water table is nearby. often forms salty crusts around edges. Plants need to be halophytic

100,000+ years to form

Death Valley , California

38
Q

Wadis

A

Fluvial

Erosion

Abrasion by ephemeral streams

100+ years

39
Q

Canyon

A

Fluvial

Erosion

Continued erosion of a wadi, or a landscape formed by exogenous rivers over millions of years

1,000+ years

40
Q

Alluvial fans

A

Fluvial

Depositional

Drop In energy due to friction with valley floor, hence sediment dropped as water spreads out in all directions . heaviest sediments dropped first, lightest further away

10+ years

41
Q

Bahadas (bajadas)

A

Fluvial

Depositional

Same process as alluvial fans - the merger of Alluvial fans

100+ years ago

42
Q

Deflation hollow

A

Aeolian

Erosion

Deflation removes sediment, leaving behind a large, shallow area, which may form an oasis if shallow enough/ close enough to the water table

100,000+ years

43
Q

Desert pavement

A

Aeolian

Erosion

Deflation removes the finest material, leaving behind gravel, rock, pebbles that are too heavy to transport

10,000 + years

44
Q

Yardang

A

Aeolian

Erosion

Differential erosion/ abrasion

10,000+ years

45
Q

Zeugen

A

Aeolian

Erosion

Abrasion

10,000+ years

46
Q

Ventifact

A

Aeolian

Erosion

Abrasion ‘mushrooms rocks’

10+ years

47
Q

Barchan dune

A

Aeolian

Deposition

Drop in energy = deposition formed in the direction of the prevailing wind . Migrate 30km/yr

5+ years

48
Q

Seif dune

A

Aeolian

Depositional

Drop in energy = Depositional. Initially formed in the direction of the prevailing wind (Barchan) then modified by secondary winds. Migrate - 10m/yr

5+ years