Desert Flashcards

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1
Q

describe hot desert regions

A
  • a large and dry region with little vegetation and high temp. Any desert has less than 250mm of precipitation a year.
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2
Q

describe the desert climate

A
  • Many hours of sunshine due to absence of clouds
  • located in sones of high atmospheric pressure
  • lack of cloud cover causes large diurnal temperature variation, 30
  • strong winds and sandstorms
  • thunderstorms may be triggered by intense connective activity
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3
Q

describe desert soils

A
  • soil is poorly developed due to lack of extensive vegetation
  • dry and sandy/red desert soils
  • lack of rainfall = lack of leaching, so with proper irrigation and soil management, plants can grow
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4
Q

describe desert plants adaptation

A
  • drought avoidance:
    > only live for a season, and store moisture/fat/sugar/proteins in seeds
    > plants use a taproot to seek secure water supplies underground
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5
Q

describe atmospheric processes as a cause for deserts

A
  • the global atmospheric circulation model (GACM) main factor distribution of deserts
  • Air rising at the ITCZ forms two tropical cells called Hadley cells
  • This air moves away from the equator and converges with a ferrel cell
  • Air sinks towards ground
    > As it towards the ground it warms
    and becomes dryer
    > And forms a high-pressure band
    30 degrees north and south,
    resulting in cloudless skys and
    low precipitation
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6
Q

describe continentality as a cause for deserts

A
  • Continentality is the way that a large land mass affects weather and climate
  • Aridity gets higher in continental interiors as the moist airstreams from the ocean are reduced
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7
Q

describe relief as a cause for deserts

A
  • moist air from the ocean moves towards a mountain
  • mountain forces air to rise, causing it to cool and condense
    > releasing rain
  • when air descends on leeward side it becomes warmer and drier
  • Atacama desert in south america
  • Andes mountain
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8
Q

describe cold ocean currents as a cause for desert

A
  • cold ocean currents cool the surrounding air
    > cold air is unable to pick up moisture
    > little precipitation
  • the cold air remains low to the ocean and increases humidity
    > may for fog and mist off shore
  • aridity is increased as rain formation is suppressed
  • sun burns away mist and fog
  • Atacama desert in South America
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9
Q

what are the three sources of energy in deserts

A

insolation, wind and water

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10
Q

what is insolation as an energy source

A
  • Insolation is the amount of heat energy that reaches the earth’s surface.
  • Insolation is high in desert regions due to the lack of cloud cover to absorb some of the suns heat energy.
  • Insolation drives many weathering processes in desert regions
  • Insolation leads to variable warming of the deserts surface which leads to wind, which can shape desert landforms
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11
Q

how is wind as an energy source

A
  • Wind is driven by the atmospheric circulation system
  • It’s an important secondary source of energy in hot deserts
  • 20-50% of deserts surfaces are covered in sand which is transported and shaped by wind.
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12
Q

what is water as an energy source

A
  • Little water in deserts
  • But it’s important in developing landscapes.
  • After infrequent heavy storms water will flow, increasing erosions rates in a short amount of time.
  • A few rives flow in deserts as well and are an important source of energy, transporting sediment and creating landforms
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13
Q

weathering definition

A
  • Weathering is the breakdown or disintegration of rocks in situ or close to the grounds surface
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14
Q

Mechanical weathering definition?

A
  • The gradual disintegration of rocks without any chemical change.
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15
Q

what is thermal fracture?

A
  • Rocks expand when heated and contract when cooled this is thermal fracture which causes them the rocks to breakdown
    > Moisture in the rocks believed to
    promote it, moister most likely
    from dew
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16
Q

what are the 4 types of thermal fracture?

A
  • Granular disintegration, granular rocks breakdown into sand, as different minerals in the rock heat up at diff rates
  • Block separation, rock with defined joints breakdown at the joint into big blocks
  • Shattering, rock without joints tent to shatter into sharp pieces
  • Exfoliation, rocks are poor conductors of heat, so the surface of the rock which is heated and cooled repeatedly flake / peel off
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17
Q

what is salt crystallisation

A
  • when it rains, the water dissolves salts in the soil.
  • the rate of evaporation draws the water to the surface, and the sal crystals are deposited on the ground surface.
  • over time the salt crystals grow and expand causing stress that breaks rocks.
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18
Q

what is frost shattering

A
  • frost shattering happens when temperatures fluctuated below and above freeing from day to night
  • freezing moisture in the cracks and pores of rocks which then expands and the contracts when it melts causing the rock to shatter
  • its not common in hot desserts
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19
Q

what is chemical weathering

A
  • rocks that change as a result of chemical action, usually in the presence of water
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20
Q

what are some example of chemical weathering

A
  • acid rain
    > CO2 dissolved in rain dissolves
    rock, mostly limestone, most
    effective in cold environments
21
Q

what are aeolian landforms

A
  • landforms made by the wind
22
Q

explain and describe the formation of this desert land from

A
  • its a ventifact
  • ventifacts are faceted cobbles and pebbles that have been abraded and shaped by wind blown sediment
    formed in the direction of prevailing winds
23
Q

explain and describe the formation of this desert land from

A
  • its a yardang
  • They are formed where vertical layers of resistant and less resistant rock are aligned to the direction of the prevailing wind
  • The less resistant rock is eroded by abrasion, forming deep troughs and leaving behind vertical, yardangs of resistant rock
24
Q

explain and describe the formation of this desert land from

A

-Zeugens form in the same way as yardangs, but the layers of resistant and less resistant rock lie horizontally
-Joints in the resistant rock widen through weathering
Abrasion deepens the furrows down into the less resistant rock beneath
-Undercutting of the furrows may also occur, to give them a pedestal shape

25
Q

explain and describe the formation of this desert land from

A
  • its a pedestal rock
  • primarily formed by aeolian abrasion
  • found in areas where isolated rock peaks are exposed to the surface and Made of alternating, horizontal bands of sedimentary rock.
  • Winds carrying fine sand particles act as an abrasive and cut the exposed rock
  • Abrasion works up to a maximum height of 2m
26
Q

explain and describe the formation of this desert land from

A
  • Accumulations of sand build into mounds and ridges
  • They become a dune when the crest is about 30 cm high and the slip-face’s angle of repose is 34°
  • Dunes grow as sand particles move up the gentle, windward slope by the processes of saltation and surface creep
  • The sand particles continually fall over the crest of the dune, onto the steeper face
27
Q

what are the two types of sand dunes

A
  • barachan
    -longitudinal dunes
28
Q

describe this type of dune

A

-its a barchan dune
- crescent-shaped dunes

  • Found in isolation in deserts where there is a limited supply of sand, but a very dominant wind direction
  • Barchan dunes form at right angles to the prevailing wind in one direction
  • They have horns that curve towards the slip face, which are pushed forward by the wind
29
Q

describe this type of dune

A
  • its a lognitudinal dune
  • linear sand dunes
  • Formed from two dominant prevailing winds in two different directions
  • They form parallel to the wind direction
30
Q

what are fluvial landforms

A
  • landforms made by weathering processes involving water
31
Q

explain and describe the formation of this desert land from

A
  • its a wadis
  • they are the deep channel systems eroded by water from runoff from torrential storms
  • wadis have thic sediment layers, loose debris from flash floods and may contain vegetation
32
Q

explain and describe the formation of this desert land from

A
  • its and inselberg
  • Inselbergs rise abruptly out of desert landscapes
  • Water (and wind) attack the original surface, leaving a round-topped inselbergs (through exhumation/uncovering)
33
Q

explain and describe the formation of this desert land from

A
  • alluvial fan
  • at the edge of mountain ranges, sediment is washed out through waides or canyons and deposited to form an alluvial fan
  • when the water reaches the planes the rushing water loses energy depositing cones of sediment
34
Q

what are bajadas

A
  • A bajada is the convergence, or blending, of many alluvial fans
  • Bajadas are common in dry climates, such as the canyons of the American Southwest
35
Q

explain and describe the formation of this desert land from

A
  • its a playas
  • playas lakes form in low areas of deserts following intense precipitation
  • they are shallow, salty and short-lived
  • when the water evaporated the dry lake bed is called a playa
36
Q

explain and describe the formation of this desert land from

A
  • Salt pans are shallow containers or depressions in the ground in which salt water evaporates to leave a deposit of salt
37
Q

explain and describe the formation of this desert land from

A
  • Canyons are formed over millions of years, when water rushes through any kind of rock
  • Formed through: D U D E
  • D - deposition, deposition of sediment from rivers builds up layers of sedimentary rock
  • U - uplift, the newly formed rock layers undergo uplift, where they rise up and form large plateaus
  • D - downcutting, hydraulic action deepens the channel of a stream or valley by removing material from the stream’s bed or the valley’s floor
  • E - erosion (not aeolian), erosion wears away at the sides of the plateaus and forms steeper gradients
38
Q

explain and describe the formation of this desert land from

A
  • its a plateau
  • a plateau is a flat topped, elevated rock landform, with at least one steep sided slope, and rises sharply above the surrounding area
  • formed by multiple process
    > collisions of tectonic plate
    > upwelling of volcanic magma
    > erosion by fluvial and glacial
    action
39
Q

explain and describe the formation of this desert land from

A
  • its a mesa or buttes
  • They have flat tops, steep eroded sides and scree slopes
  • Wider than they are tall
  • Mesas are remnant parts of a larger table-top plateau
  • Buttes are remnant mesas that have undergone further weathering and erosion, and are taller than they are wide
40
Q

explain and describe the formation of this desert land from

A
  • its a pediment
  • it forms at the foot of a steep slope or cliff by running water
  • they have a gentle erosional surface with a low relief of 2-7 degrees
  • they mark change of angle from the cliff face and the pediment plain
41
Q

explain and describe the formation of this desert land from

A
  • its a desert pavement
  • its a desert surface covered by rock fragments
  • formed when wind blows away the finer sand, leaving behind larger rocks
42
Q

what are the three forms of wind erosion

A
  • deflation
    > the carrying and
    removal of loose material
    by the wind
  • abrasion
    > wind laden with sand carves
    and sculpts rock, usually
    within 2m of the desert floor
  • attrition
    > loose materials collide with
    each other and become
    smaller
43
Q

what are the three types of wind transportation

A
  • surface creep
    > when sediment (>0.25mm)
    slide and roll across the
    surface
  • saltation
    > when wind is strong, larger
    particles begin to bounce
    close to the ground
    > the particles to big to go long
    distance, and only reach a
    height of 10cm
  • suspension
    > small particles (<0.15mm) are
    carried by strong wind into
    the atmosphere
44
Q

what is deposition

A
  • deposition happens when wind drops
    below the threshold velocity to carry particles in suspension
45
Q

what are the sources of water in hot deserts

A
  • episodic flash flood
    > infrequent rainfall events, involving intense
    rainfall or a storm
    > the sunbaked soil / sand leads to high runoff
    and erosion
    > the water will either flow as a sheet (sheet
    flooding, or in channels (channel flash
    flooding)
  • Ephemeral rivers
    > intermittent rivers that only flow for part of
    the year, often after intense rainfall
  • endoreic rivers
    > rivers that flow into deserts but terminate in
    a lake or inland sea
  • exogenous rivers
    > rivers that have their source outside of the
    desert and flow year round
46
Q

what are the types of water erosion

A
  • hydraulic action
    > the sheer force of the river
  • abrasion
    > sandpaper effect of loose rock carried by the
    water
  • corrosion
    > the dissolving of rock in slightly acidic water
  • attrition
    > fragments of rock carried by the water
    hitting into other rock
47
Q

what are the types of water transportation

A
  • traction
    > rolling sediment along the channel
    bed
  • saltation
    > bouncing of particles along the
    channel bed
  • suspension
    > sediment carried within the body of
    the water
  • solution
    > dissolved sediment in the water
48
Q
A