Desert Flashcards
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.
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
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
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
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
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
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
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
9
Q
what are the three sources of energy in deserts
A
insolation, wind and water
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
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.
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
13
Q
weathering definition
A
- Weathering is the breakdown or disintegration of rocks in situ or close to the grounds surface
14
Q
Mechanical weathering definition?
A
- The gradual disintegration of rocks without any chemical change.
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
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
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.
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
19
Q
what is chemical weathering
A
- rocks that change as a result of chemical action, usually in the presence of water
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
