Landforms CH 11

Have today's deserts always been deserts?

No, these landscapes used to be fields and forests but weathering, location, and temperature all played a role to turn it into a desert.

How can desertification in Africa affect the Caribbean?

Wind can blow particles from Africa into the Caribbean, some of them potentially toxic.

rain shadow desert

a dry area on the lee side of a mountain range

polar desert

a high-latitude region that receives very little precipitation

hogback

a narrow, sharp ridge formed on steeply inclined resistant rock

Bornhardts

a type of inselberg that has a loaf shape

dust storm

a windstorm that lifts up clouds of dust or sand. can be 100 km long and 1.5 km high

longitudinal dunes

abundant sand and a strong, steady wind, axis lies parallel to the wind direction

cuesta

asymmetric ridge that form in places where bedding dips at an angle

Why are playas found in almost all basins of the basin-and-range region?

because the depressions in the basins are ideal for the accumulation and evaporation of water

Why are alluvial fans and bajadas so common in the basin-and-range desert?

because there is a lot of canyons and flash floods occur periodically

What is a process that can change a mesa into a butte or pinnacle?

cliff retreat

coastal desert

cool dry air blows in from the ocean and evaporates occurs as it warms

barchan dune

crescent shaped dune, when sand is scarce and wind blows steadily in one direction

blowout

deflation on the land surface that scours a deep, bowl like shape

a lag deposit is also called a

desert pavement

What causes the process of desertification?

diversion of water, overpopulated arid areas, careless agricultural processes, overgrazing in arid areas, natural droughts

arid

dry

playa

dry, flat, exposed lake bed that come from desert lakes evaporating entirely

talus aprons

eroded bedrock form around cliff faces

suspended load

fine grain sediment such as dust and silt held in suspension

arches

formed when erosion along joints leave narrow walls of rock, having the lower part of the wall eroding while the upper part remains

Desertification

gradual transformation of temperate land to desert

ephemeral (intermittent) streams

have flowing water either episodically or during a portion of the year

cold deserts

high latitudes, high elevations, near cold ocean currents and stay below about 20 deg C for the year

subtropical desert

hot temperatures, extremely dry conditions, and sparse vegetation

Continental Desert

in continental interiors far from moisture sources

inselbergs

isolated, steep-sided erosion remnants that rise above desert plains

mesas

large, flat-topped hills

subtropical region

latitudes of 20-30

effects of desertification

loss of economic activity due to damage to agriculture, change of climate, reduction in species and biodiversity

buttes

medium-sized, flat-topped hills in an arid region.

which type of weathering is dominant in deserts

physical

sand dune

pile of sand deposited by a moving current

What two special conditions in deserts that tend to make fluvial erosion more likely when it does rain?

poor infiltration and lack of vegetation

deflation

process of lowering the land surface by wind erosion

water erosion in deserts

rainfall, sheetwash, and stream flow; causes more erosion than wind

how do you slow/stop the process of desertification

reduction in farming, cattle grazing and increase in vegetation

ventifacts

rocks shaped by wind blown sediments

what is the most important process of erosion and deposition in arid environments?

running water

chimneys

small sized, flat topped hills in arid regions

Desert characteristics

supports vegetation on no more than 15% of land, less than 25 cm of rainfall per year

hot deserts

temps exceed 35 deg C

desert varnish can reveal what about a desert?

that a desert surface has been exposed for quite some time as desert varnish takes a long time to form

lag deposit

the coarse sediment left behind in a desert after wind erosion removes the finer sediment

bajada

the elongated wedge shaped area between overlapping alluvial fans

alluvial fan

the network of distributaries that spread the sediment out into a broad fan, wedge or apron shaped pile of sediment

calcrete

when minerals that bind clasts together to form a new rock-like material

transverse dunes

when sand accumulates to bury the ground surface completely, and only moderate winds blow sand piles into simple, wave-like shapes

When do dunes form?

when sand becomes trapped on the windward side of an obstacle (rock or shrub)

parabolic dunes

when strong winds break through transverse dunes and change them into a parabolic shaped dune

When does Saltation begin?

when turbulence caused by wind shearing along the ground surface lifts sand grains

what creates smooth surfaces on rocks and boulders in the desert?

wind abrasion

star dune

wind shifts direction frequently, a group of crescents pointing in different directions overlap one another, constantly changing

desert varnish

A dark, rusty-brown coating of iron oxide and magnesium oxide that accumulates on the surface of the rock.

If the sand is relatively scarce, but the winds blow steadily in one direction the dunes that most likely will be formed are called___

Barchan Dunes

Why does the leeward side of a dune (the slip face) have a steeper slope than the windward side?

Because that is where sand "slips" down

types of deserts

Subtropical Continental Interior Rainshadow Coastal Desert Polar Desert

The Namib Desert lies to the north and west of the Kalahari Desert, in southern Africa. The reason that the former region is a desert is not the same as the reason that the latter is a desert. Explain this statement.

The Namib desert formed due to cold ocean currents which created dry air and decreased precipitation but the Kalahari formed due to its location's latitude and atmosphere

cliff retreat

The change in the position of a cliff face caused by erosion.

What factors determine which type of dune develops at a particular location?

The characteristic of wind and sand supply

saltation

The movement of sand or other sediments by short jumps, bounces, and rolls that is caused by wind. Saltating grins generally rise no more than 0.5m, but where sand bounces on bedrock, it may rise 2m.