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GEO1009F > THE WORK OF WIND > Flashcards

THE WORK OF WIND Flashcards

1
Q

difference in physical laws of fluid motion of water and wind

A

wind is less contrained by gravity and unconified

e.g. wind can blow uphill

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2
Q

wind is less effective agent of erosion, deposition and transport

what are the exceptions to this

A

arid zone – some times whole landscapes are product of aeolian processes

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3
Q

what and were is the Rub al Khali?

A

Saudi Arabia

surface water free dunefield

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4
Q

where is wind action most important

A

drylands
deserts
coasts

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5
Q

water as a sculpting agent in deserts

A

also played a significant role

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6
Q

what are deserts?

A

places where surface water is limited in quantity

arid zone geomorphology

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7
Q

what is aridity?

A

combination of low moisture input and high moisture output doe to low precip and high evap

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8
Q

aridity index

A

ratio between precip and evap

precip/potential evaptrans

P/PET

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9
Q

what is aridity characterized by?

A

as net surface water deficit caused by global atmospheric, oceanographic and topographical factors

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10
Q

global atmospheric, oceanographic and topographical factors

A

1) Atmospheric stability due to global air mass dynamics
2) Atmospheric stability due to cold ocean currents
3) Continentality

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11
Q

atmospheric stability arising from global air mass dynamics

A

Arid areas form in zones of dry, descending, stable air over the sub-tropical high pressure belts.

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12
Q

atmospheric stability induced by ocean currents

A

Cold ocean currents associated with descending stable, dry air
The cold Benguela current and associated upwelling ‘causes’ the Namib desert

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13
Q

aridity induced by ‘continentality

A

Distance from the oceans prevents penetration of rain-bearing winds,

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14
Q

Aridity induced by topography

A

So-called rain shadows, where mountains act as barriers to the penetration of rain-bearing winds, e.g. Tanqua (Ceres) Karoo.

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15
Q

where are deserts?

A

one third of arid zones falls within africa

Global extent of drylands Dry-subhumid 10 Semi-arid 18 Arid 12 Hyperarid 7
Total 47

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16
Q

where are landform features shaped by the wind are found

A

where wind blows frequently and at high velocities and where entrained particles are blasted against easily disintergrated surfaces

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17
Q

what are four types of landforms produced by wind erosion

A

a) deflation hollows
b) desert pavements
c) ventifacts
d) yardangs

18
Q

what is the key process in creating wind produced landforms

A

abrasion/ attrition

19
Q

deflation hollows

A

removal by wind of sand and silt particles producing a local lowering of the land surface

‘Blow-out’ may then expands over time due to collection of runoff and intensification of weathering associated with fluctuating groundwater (results in a ‘pan’).

20
Q

where do deflation hollows occur?

A

where vegetation cover is broken

21
Q

desert pavement

A

deflation may remove finer grained particles and leave behind a lag layer of gravel

22
Q

ventifacts

A

abrasive action of etrained material causes grooving and polishing of surface rocks - wind faceted stones

are results from impact by suspended and saltating particles - sandblasing

complex shapes and sculpturing

23
Q

yardangs

A

duplicates of ventifacts on a much larger scale

inverted boat

well developed in soft sediments

24
Q

wind transport of sand

A

transport is maximized in grain size of 0.04mm - 0.4mm

grains have characteristic physical feature

wind turbulence promotes uplift and entrainment

25
Q

how does sand move

A

creep

saltation

26
Q

hjulstrom equivalent for wind

A

see slides

27
Q

creep and saltation of sand

A 
creep = rolling along bed
saltation = jumping
28
Q

what is dust

A

generalised term that accounts for fine particles

29
Q

dust grain size

A

10-100 microns

30
Q

transport of dust

A

dust can travel very far
dust from sahara may be principal supplier of nutrients to amazon rain forest
can remain in suspension for very long time
dust storms

31
Q

what causes aeolian deposition

A

reduction in wind energy - loss of competence

32
Q

what happens if the entrained particles are sand sized?

A

formation of discrete landforms dunes

33
Q

what are the controlling factors of dune types

A

sand supply
grain size
wind velocity, frequency and direction

34
Q

main dune types

A 
barchan
transverse
longitudinal
star
parabolic
35
Q

barchan

A 
barchanoid dune
cresent shape often in groups 
horns point in wind direction 
commonest in areas of limited sand supply
high migration rates
36
Q

transverse dunes

A

can result from barchan coalescence to form irregular ridges – ridges are perpendicular to wind direction
found in areas of abundant sand supply and no vegetation
slower migration rates

37
Q

linear/longitudinal or seif dunes

A

long straight ridges parallel to prevailing wind direction
moderate sand supply
dunes are sediment accumulators
migrate slowly

38
Q

parabolic dunes

A

like barchans but their horns face opposite to wind direction

39
Q

environmental implications of desertification

A

Human activities may induce the spread of desert-like conditions and, in the classical model, this involves the invasion of non-desert areas by mobile dune forms or the reactivation of stabilised dunes.

many and complex (include ‘drought’, grazing and crop mismanagement, climate change) but impacts are often severe (e.g. famine) and the consequences dire.

40
Q

Kalahari case study

A

largest area of inactive sand dunes (vegetated or fossile dunes)

Active in the relatively recent geological past under conditions drier/windier than present

41
Q

What about the future under predicted climate conditions in a warmer earth?

A

widespread reactivation of ‘fossil’ dune forms

GEO1009F (16 decks)

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