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GLGY201 Principles of Geoscience > Deserts and Wind > Flashcards

Deserts and Wind Flashcards

1
Q

What is a desert?

A

a region that receives less than 25cm of precipitation per year

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2
Q

Life support in a desert

A

deserts are unable to support significant populations of animals because the vegetation is so sparse, and water is so rare

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3
Q

Temperature in a desert

A

Extreme temperature ranges because the atmosphere contains little humidity to block the Sun’s rays or retain heat at night

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4
Q

Natural Climate Change

A

climates can change naturally, i.e the Sahara region was humid 5k to 10k years ago

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5
Q

Deserts may be hot or cold, but

A

low precipitation is a common trait

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6
Q

Top 3 largest deserts

A

Antarctic desert, Arctic desert, and Sahara

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7
Q

Some would argue that the “Arctic Desert” isn’t really a desert. Why do most cool dry areas have more vegetation than hot dry areas?

A

Life is better at dealing with cool than hot, can conserve water better

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8
Q

Atmospheric moisture circulation determines the location of most deserts

A

arid belts are where deserts are because of the way air moves up then cools off and precipitates

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9
Q

Formation of Deserts

A
  • Air warms and contracts as it sinks closer to Earth’s surface
  • Evaporation exceeds condensation
  • Deserts form, clustered around 30ºN and 30ºS latitudes
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10
Q

Not all deserts lie around 30º latitude. Several other factors contribute to desert locations:

A
  1. Orographic effect
  2. Dry, cold air descending over polar regions
  3. The distance atmospheric moisture is transported
  4. Cold ocean current adjacent to a tropical coast
  5. Poor management of farmland
  6. Deforestation
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11
Q

Orographic effect

A
  • When air masses are forced to flow over high topography.
  • As air rises over mountains, it cools and water vapour condenses.
  • As a result, it is common for rain to be concentrated on the windward side of mountains, and for rainfall to increase with elevation in the direction of storm tracks.
  • The other side of the mountain has arid conditions
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12
Q

Rainshadow

A

The side of the mountain that has arid conditions b/c precipitation is on the other side of the mountain

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13
Q

The distance atmospheric moisture is transported, more distance =

A

less precipitation further away/further inland b/c it’s precipitated out as it travels

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14
Q

Cold ocean current adjacent to a tropical coast = warm currents are much more likely to:

A

evaporate and precipitate, cold currents create much less

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15
Q

Poor management of farmland = decertified by:

A

removing all the foliage via agriculture

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16
Q

Deforestation = removal of

A

biomass, dries out soil

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17
Q

Everything comes back to the ocean because:

A

it is the heat sink on the planet and distributes the heat around.

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18
Q

What dictates the ocean current?

A

Location of the continents.

- As they move they change the ocean currents’ routes and changes the distribution of heat = changing the climate

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19
Q

Trade Wind Deserts

A

An area of very little rainfall and high temperature occurs where the trade winds or their equivalent (such as the harmattan) blow over land.

20
Q

Mid-latitude Deserts

A

near the equator basically

21
Q

Rain Shadow Deserts

A

A patch of land that has been forced to become a desert because mountain ranges blocked all plant-growing, rainy weather. On the rain shadow side has all precipitation is blocked.

22
Q

Coastal Deserts

A
  • Occur in cool to warm areas along the coast.
  • Cool winters and long, warm summers.
  • Located on the west coasts of continents between 20° to 30° latitude.
  • Winds off the coast blow in an easterly pattern and prevent the moisture from moving onto the land
23
Q

Wind is an important geological agent, has much less

A

carrying capacity, but can still move a lot and create structures

24
Q

Stoss slope

A

Windward slope (less steep)

25
Q

Slip face

A

lee slope (more steep)

26
Q

Suspension

A

silt carried in suspension produces well-sorted deposits of progressively smaller sediments with distance

27
Q

Loess

A

eolian deposits of silt are left by continental glaciations

28
Q

Mineralogically, how does loess differ from typical wind-blown sand?

A

Significantly finer sand, significantly less mature, short transport distances = more clays involved.

29
Q

Desert Structures

A
  • Desert pavement

- Yardang

30
Q

Desert pavement

A

lag deposit of coarse sediment left after fines blow away

31
Q

Yardang

A

rock outcrop sculpted by sand abrasion

32
Q

Sand Dunes Reflect Sediment Availability and Dominant Wind Direction (need these characteristics)

A
  • Wind: direction of the wind, the strength of wind
  • Abundant loose sediment (usually sand)
  • Energy to move sediment (usually wind)
  • An obstacle to trap sand (often a bush)
  • A dry climate
33
Q

Dune Terminology

A
  • Barchan
  • Transverse
  • Parabolic dune
  • Longitudinal dune
  • Star dune
  • Sand seas
34
Q

Barchan (crescentic dune)

A

Shape: crescent moon, horns point downward (stereotypical crescent moons)
Wind characteristics: constant wind from one direction
Environment of Deposition: limited vegetation and sediment, often on flat bare rock
Grain Characteristics: well-sorted, very fine to medium sand

35
Q

Transverse (crescentic dune)

A

Shape: long, wavy, linear, orientated perpendicular to wind direction (look like rolling pointy hills)
Wind Characteristics: constant, moderate wind from one direction
Environment of Deposition: limited vegetation, more sediment than barchan
Grain Characteristics: well-sorted, very fine to medium sand

36
Q

Parabolic dune

A

Shape: crescent moon, horns point upwards (look like crescent moons with “massive tails”, basically elongated c shape, centre of c is where wind is blowing)
Wind Characteristics: variable strength, unidirectional wind
Environment of Deposition: Abundant supply of sand and vegetation common
Grain Characteristics: well-sorted, very fine to medium sand

37
Q

Longitudinal dune

A

Shape: large, straight or sinuous sand ridge, generally longer than wide (parallel weird ripple shape)
Wind Characteristics: strong, steady winds that blow from two directions
Environment of Deposition: form in parallel sets of sand ridges
Grain Characteristics: well-sorted, very fine to medium sands

38
Q

Star dune

A

Shape: pyramid, 3 or more arms radiate from a peaked center (giant sand volcano)
Wind Characteristics: wind blows from several different directions
Environment of Deposition: grow taller rather than migrating
Grain Characteristics: well-sorted, very fine to medium sand

39
Q

Sand seas

A
  • Large regions (>125km^2) of windblown sand numerous
  • Very large dunes
  • Sand covers >20% of the ground surface
  • Self-explanatory visual
40
Q

Differences in shape and wind characteristics of Barchan and Parabolic dunes?

A

Barchan: shape: crescent moon with horns that point downwind. Wind: constant wind from 1 direction

Parabolic: shape: crescent moon with horns that point upwind. Wind: variable strength, unidirectional wind

41
Q

Arid Landforms

A
  • Can be shaped by water
  • Flash floods are common
  • Streams tend to be ephemeral, flowing only after heavy rain
42
Q

Playa Lakes

A

Products of rainfall and evaporation, trapped body of water

43
Q

What evidence is there that this area was recently wet?

A

Mudcracks

44
Q

Desertification

A
  • Process by which land loses its vegetation and turns into a desert
  • Threatens all six inhabited continents
45
Q

Both natural and anthropogenic factors lead to desertification. What are some of the factors?

A

Animals eating all the vegetation

46
Q

Desertification leads to environment refugees

A

Mass migration of humans away from deserts

GLGY201 Principles of Geoscience (20 decks)

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