Chapter 15 -- Deserts and Stuff Flashcards
An area with less than ##cm (## inches)of annual precipitation.
_______ may be cold, temperate, or hot. All major continents have one type of desert or the other.
In desert regions the wind is an effective agent of ________ and _________ due to a lack of water.
Covers about ##% of the land on Earth.
Desert
Erosion and Transportation
25cm (10in)
The expansion of deserts into formerly productive lands.
These expansions destroy croplands and rangelands.
Causes starvation forcing people from their homelands
Main causes are drought and overpopulation
Closely related to global warming
Desertification
Signs of Desertification (6)
Lowering of water table
Marked reduction of water supply
Increased salinity in water and soil
Progressive destruction of native vegetation
Accelerated soil erosion
Death of cattle - water dependent - foods
Material too large or heavy to be carried in suspension by water or wind.
Particles are moved along the surface by saltation, rolling, or sliding.
Bed Load
Material that can be carried in suspension by water or wind.
Composed of silt and clay sized particles.
Can be carried for thousands of kilometers.
Suspended Load
Wind erosion can be caused through
Abrasion or Deflation
Is the impact of saltating sand grains on an object. Its effect is similar to sandblasting.
Abrasion
Stones whose surfaces have been polished, pitted, grooved, or faceted by the wind.
They are a common artifact of abrasion.
Ventifacts
Is the removal of loose surface material by wind.
Deflation
Is left behind after wind has removed the finer grained material and it protects the underlying material from deflation.
Desert Pavement
Occur in several distinctive types, consist of sand, and are deposited near their source and covers ##% of the land.
Mounds or ridges of wind deposited sand close to its source
Form when wind flows over and around the obstruction, resulting in the deposition of sand grains, which accumulate.
Dunes
10%
Consists of windblown silt and clay deposits composed of angular quartz grains, feldspar, micas, and calcite often found far from their source and covers 10% of the earth’s land and 30% of the US
Sources: Deserts, Pleistocene glacial deposits, floodplains.
Erode easily
Weathers to a rich, fertile soil.
Loess
Types of Sand Dunes
Crescent shaped dunes whose tips point downwind
Form in the areas that have a generally flat, dry surface with little vegetation, a limited sand supply, constant wind direction.
Most mobile dune, up to 10m/yr
Barchan Dune
Types of Dunes
Long, parallel ridges of sand aligned generally parallel to the direction of the prevailing winds.
Form where the sand supply is somewhat limited.
Can be up to 100m high (common in Egypt and Australia)
Longitudinal Dunes
Types of Dunes
Form long ridges perpendicular to the prevailing wind direction
Found in areas that have abundant sand and little to no vegetation.
Crest up to 200m high.
Transverse Dunes
Types of Dunes
Common in coastal areas
Features: abundant sand, strong onshore winds, tips point upwind, anchored by vegetation, center is often blown out.
Parabolic Dunes
Types of Dunes
Several ridges radiate from the crest.
Features: variable wind direction, stable dunes with which many are landmarks for desert travelers.
Star Dunes
Warm air rises, cool air sinks
Low pressure systems are dominant at ___ altitudes, high pressure at _____
Descending atmosphere cells in between result in another high pressure system.
The _______ effect describes the deflection of winds in the hemispheres due to the rotation of the Earth.
Low Altitudes
Poles
The Coriolis Effect
The majority of the world’s deserts are located between ## and ## degrees north and south latitudes.
20 and 30
Mountain ranges may block the flow of moist marine air creating a “____ ______”
Many middle and high latitude deserts are located far from the coast.
Rain Shadow Effect
Most Deserts are characterized by…(5)
Widely vary temperatures – extreme highs and lows
a sparse plant cover
little precipitation at less than 25cm/year
plants are diverse, yet widely spaced, small, and slow growing
leaves are usually hard and waxy
\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_\_ is dominant, coupled with slow rates of \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_\_, results in poorly developed soils. \_\_\_\_ \_\_\_\_\_\_\_\_ (\_\_\_\_\_ \_\_\_\_\_\_\_) coats many rocks with iron and manganese oxides.
Mechanical Weathering Chemical Weathering Rock Varnish (Desert Varnish)
________ _________ is a major agent of erosion in deserts
Running Water
_____ is capable of producing a variety of distinctive erosional and depositional features.
Wind
________ ___________ describes a desert stream that never reaches the sea, depositing its load within the desert.
Internal Drainage
Elongated streamlined ridges that look like an overturned ship’s hull.
Yardang
Desert Landforms
Results from the evaporation of temporary lakes.
Most shallow and have shifting boundaries.
Evaporates to form a playa.
Characterized by mud cracks and salt crystals
Salts are often concentrated enough to be mined commercially
Playa Lakes
Desert Formation
Form when sediment laden streams flow out from mountain fronts into the flat desert floor.
Poorly sorted, fans out from the mouth of the stream
Similar in shape and origin to deltas
Coalescing ________ ____ form ________.
Alluvial Fans
Bajadas
Desert Landforms
Erosional bedrock surfaces
Low relief
Slope gently away from mountain bases
Pediments
Desert Landforms
Isolated, steep sided erosional remnants that rise above desert plains.
Inselbergs
Flat topped, pillar like, erosional remnants with steep slopes
Buttes
Flat topped, table like, erosional remnants with steep slopes
Mesas
