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34 Cards in this Set
- Front
- Back
Covers
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25% of land surface
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primary control on deserts?
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plate tectonics
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unique qualities
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extreme dryness
may be hot or cold specialized ecosystems low human population unique geologic processes |
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deff of desert
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land that is so extremly arid that :
evaporation prevents permanent surface water |
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hot desert
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low latitudes
low elevations far from oceans |
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cold desert
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high latitudes
high elevations near cold ocean currents |
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land surface features
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exposed bedrock
accumulated clasts unweathered sediment precipitated salt windblown sand |
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five types of deserts
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subtripical deserts
rain shadow desert coastal deserts continental interiors polar desert |
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subtropical desert
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earth's largest
form due to patterns of atmospheric convention found at 20 to 30 degrees N and S latitude across geologic time |
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rainshadow desert
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moist ocean winds are driven over mountains
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coastal deserts
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-cool air over ocean water hols little moisture
-air is absorbs moisture when it interacts with land -the atacama desert is the driest place on earth |
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interior deserts
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-hair loses moisture as it crosses contients
-land far from ocean moisture can be arid ex: gobi desert |
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polar deserts
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-Above 66º N and S latitude there is little moisture.
-Air circulation carries dry air to polar regions. -It is so cold; the air can’t hold moisture. |
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desert processes
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deserts are characterized by special processes:
-eronsion by water and wind -weathering -soil formation -deposition |
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weathering
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Physical weathering dominates.
-Rare chemical weathering leaches ions. -Evaporation salts both break and cement grains. |
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desert varnish
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Exposed surfaces develop desert varnish.
Dark surface coating of iron and manganese oxides. Forms very slowly by bacterial activity, dust, and water. Native Americans left petroglyphs in desert varnish. |
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desert soils
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-Desert soils are thin, with poorly defined horizons.
-They usually are colored like the bedrock nearby. -Trace elements orchestrate wide color variations. |
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water erosion
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Though rare, water shapes landscapes.
-Lack of roots magnifies sediment erosion and transport. -Torrential rains generate dangerous flash floods. -Rapid flow of thick, muddy, and viscous water. -Flash floods quickly infiltrate dry stream beds. |
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wind erosion and transport
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-Sparsely vegetated ground is scoured by wind.
-Sand and silt-sized sediment is lifted and moved. -Surface load – Grains moved in contact with land surface. -Saltation – Sand skipped and bounced by grain impact. -Suspended load – Sediment carried in the air. -High winds can carry dust across entire oceans. |
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wind erosion and transport
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-Coarse clasts cannot be lifted and moved by wind.
-Lag deposits form when finer sediment is removed. -Form desert pavement, a surface layer of stones. |
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deflation
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lowering the land surface via erosion
-concentrated wind erosion creates a blowout - ex: mars |
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desert deposition
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-desert sediments accumulate in many seetings
-erosional debris accumulates near source areas |
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alluvial fans
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conical accumulations of sediment
-water exiting a canyon spreads out and drops sediment -grow outward from source over time |
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playas
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desert lakes that have no outlet streams
-internal drainage collects water from flash floods -dissolved solids crystallize out as water exaporates |
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surface load
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coarser sand-sized particles
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suspended load
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finer-grained silt-sized dust
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bedrock controls landforms
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bedrock exposed along cliffs breaks away along joints
-cliff retreat in flat rocks creats plateaus then mesas -then buttes and finally chimneys |
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stony plains
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sloping gravelly alluvial plains
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pediments
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ramp like surfaces that slow up toward a mountain front
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dunes
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windblown accumulations of sand
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dunes depend on
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wind - velocity and consistency of direction
sediment supply - is sand scarce of abundant |
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desertification
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aridificcation of non-desert areas
-human activity expands desert areas |
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desertification is caused by:
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overpopulation
overgrazing careless agriculture diversion of water supplies |
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large dust storms..
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cross entire ocean basins
carry diseased organismed |