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DESERTS, GLACIERS AND
CLIMATE CHANGE
Objectives
• Identify five different geologic settings for deserts.
• Describe the structure of a sand dune.
• Distinguish between several different kinds of glaciers
and ice formations.
• Describe how ice in a glacier changes form,
accumulates, ablates, and moves.
• Explain how geologists learn about past climatic
conditions.
• Examine evidence for anthropogenic climate change.
Deserts and Drylands
• Types of deserts
– Desert
• An arid land that receives less than 250 millimeters of rainfall or
snow equivalent per year
• Sparsely vegetated unless it is irrigated
• Different types depending on location and global air circulation
patterns
– Subtropical desert: located between the 30°N and 30°S latitudes
– Polar desert: located in polar regions; precipitation is primarily snow
which does not melt
– Continental interior desert
– Rain-shadow desert
– Coastal desert
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Deserts and Drylands
Deserts and
Drylands
Deserts and Drylands
• Erosion- Wind blown sediment
– Surface creep
• sediment transport in which the wind causes particles to roll along
the ground
– Saltation
• Sediment transport in which particles move forward in a series of
short jumps along arc-shaped patterns
– Suspension
• Sediment transport in which the wind carries very fine particles over
long distances and periods of time
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Deserts and Drylands
• Wind erosion continued
– Mechanics of wind erosion
• Abrasion
• Airborne particles chip
small fragments off rocks
protruding above the
surface
• Deflation
• Loose particles of sand
and dust are removed by
wind
• Leaves coarser particles
behind
Ventifacts (South Sinai)
Ventifacts-Iceland
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Yardangs
Iran-largest on earth
White Desert, Egypt
White Desert, Egypt
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Deserts and Drylands
Desert pavement
• Theories for origin
– Winnowing of fines by
wind or water
– Heave of larger clasts
due to swelling of
clays or formation of
salt crystals.
– Others
Desert varnish
• Coating of
manganese oxides on
exposed rock
surfaces. Involves
oxidation and
precipitation by
microorganisms that
can live in very
alkaline conditions.
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Desert varnish on
Cretaceous sandstone,
Kurkur plain, southern
Egypt.
Dark surfaces on inselbergs and surface pebbles is
desert varnish
Landforms
• Stream valleys-wide shallow channels, high
bedload transport
• Desert plains and plateaus
– Bare surfaces (lack of vegetation)
– Stony-lag concentrate from wind erosion (reg)
• Desert pavement, rocks in close contact, may be covered
with desert varnish
– Barren rock (hammada)
– Sand seas (ergs)
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Reg surfaces
Giza Plateau El-Qaa Plain,
Sinai
Hammadas
Erg: Sand Sea
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Deserts and Drylands
• Wind deposits and landforms
– Dune
• A hill or ridge of sand deposited by winds
– Slip face
– Cross beds
– Angle of repose
Deserts and Drylands
Slip face; Mt. Baldy,
Indiana Dunes
National Lakeshore
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Deserts and Drylands
Cresent=Barchan
Dunes
Incr.
Sand
supply
Barchans
Wind from one direction; limited
sand supply; horns point
downwind; slip face is always
steeper
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Barchans near the 3rd cataract: Dongola,
Sudan
1 mile
Longitudinal (linear) dunes
Namibia; USGS
Wind from 2 directions:
limited sand supply
Great Sand Sea, Western Desert
5 miles
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Transverse dunes
Wind from one
direction:
abundant sand
supply
Parabolic (blowout) dunes
Erosion of existing
dunes; horns point
upwind.
Deserts and Drylands
Wind from more than 2
directions; abundant sand
supply
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Deserts and Drylands
• Stream erosion and
deposition
– Arroyos
– Flash floods
– Alluvial fan
• Desertification
– Invasion of desert
conditions into non-desert
areas
• “Dust Bowl”
Flash floods are common in
mountainous desert areas
because:A) Steep slopes
B) Sparse vegetation
C) Intense rainfalls
Flash floods
• En Gedi
• Wadi Zin
• El Arish, 2010
Shortcut to En Gedi floods.lnk
Shortcut to Zin2.lnk
Wadi e l A resh.flv
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Deserts and Drylands
