Ch 18 Flashcards
Thin or absent. Exposes bedrock to weathering/erosion contributes to stark, rigged, rocky terrain.
Soil regolith
Mechanical weathering is dominant, chemical weathering is absent in the DRYEST deserts, salt wedging is more common in the not humid areas.
Weathering
Surface like cap-rock and hardpans-high runoff terrain. Resistant bedrock surface. Hardened/water impermeable.
Impermeable surface
Not all deserts are a sea of sand. -high sand proportions have 3 influences. 1. Sandy cover allows water to infiltrate the ground, inhibiting via streams and overland flow. 2. Sand is moved by heavy rain. 3. It can be transported & redeposited by wind.
Sand
Usually very intense, but short, cover a limited area, fluid erosion and deposition is effective and conspicuous.
Rainfall
Almost all streams are ephemeral, only during and immediately after rain.
Fluvial deposition
Most desert drainage terminus is a basin or valley with no external outlet. No stream/sea
Basin of interior drainage
Lack if vegetation Is the single most significant feature that provides little protection from raindrops or function inadequately to bid the surface material w/roots. Really spread out.
Vegetation
Impermeable surface-sand (which is separate soil but not ACTUAL soil) in softened regolith soil, vegetation. Gives the concave Angularity of desert slopes
Soil creep
FLUVIAL deposition, vegetation, even if scarce every desert had plants. -high rapid runoff
Rainfall
Mechanical weathering in no veg. Area without water
Chemical weathering where whetstone and water resides .
Dry climates
Moist climates
Scarce vegetation
Great volumes of sediment moved in short time
Over land flow
Running water in waterless regions
Exotic streams
Ephemeral streams
Desert lakes
Surface water deserts
The nile river, Colorado river
Water comes from mountains
In dry lands the flow diminishes downstream, the water seeps into the river bed or evaporates, and it is directed for irrigation. In humid areas it is nourished .
Exotic streams
More than 99% of desert streams.
Cause the most intense erosion/ transportation/ and deposition.
Ephemeral lakes
Dry lake beds
- playas
- playa lakes
Desert lakes
Temporary lakes built form playas water.
Playa lakes
Flattest most level land forming. Salina of salt. Dry lake bed.
Playas
The most permanent desert lakes are
Saline lakes
Only during small portion f the year.
Mechanically weathered and erosion results in steep rocky surfaces.
FLUVIAL erosion in arid lands
Hardness of rock layers differs.
Rocks resistant to weathering and erosion form cliffs pinnacles spires or sharp crests. Soft rocks produce gentle slope surfaces and features
Differential erosion
A residual erosional surface.
“Island mountains” very resistant.
Inselbergs
Ephemeral stream deposit channels
FLUVIAL deposition in arid lands
Entry inclined bedrock platform. A residual surface. Left by weathering and removal of rock NOT deposition.
Pediment
Any zone or foot of mtn. range.
Area of FLUVIAL deposition.
Piedmont areas
More notable and found in desert landscapes
Talus accumulations
Deposit Above piedmont angle
Alluvial fan
Ergs
Regs
Hamada
Characteristic desert surfaces
Stony desert
Arabic for stone, desert pavement. Surface pebbles for closely together sealing material form further erosion. “Desert armor” gibber plain in Australia . Flat.
Reg
A sea of sand. “Arabic for sand. As high as sand dunes.
Erg
Rock. Little loose material. Exposed bedrock. Sediment is cemented by salt material. Flat,
Hamada
Basin and range terrain
Mesa and scarp terrain
2 representative desert landform assemblages in US deserts
3 influences range
Piedmont zones
Basins
Basin and range terrain
Mountain “” dominate the horizon in all directions. Ruggedness, steep, rocky
Ranges
"”At the base of mountain ranges sharp break in slope marks change in range to basin floor “ transition area” area of FLUVIAL deposition. (Rarely visible)
Piedmont zone
Flattish floor of basin, very gentle slope from all sides, playa is the low point.
Basin
Presence of “” gives a brilliant white color to the playa or Salina surface.
The “” lakes are clear, with salty froth on edges .
The “” lakes are muddy, lack “” to make silt settle.
Salt
Salina
Freshwater
Salt
Vast CA’s topographic museum. Primer basin and range terrain. Down dropped “valley” basin. Result of crustal extension taking place throughout basin & range. 150 mi long trough. 4-16 mi range. Not a classic graben.ore tilted on east side. “Pull apart” basin. Formed where land drops between 2 parallel strike slip faults. Valley 86 meters below sea level. Rocky barren and rugged surroundings untwined. Steep erosion and slopes. Flat surfaces led topographic features hard to sea l. Incredible depth of alluvium.
Death Valley
“Table” & “escarpment” flat topped surfaced horizontal layers of rock. Slopes have multiple scraps. Deferential weathering. Residual landforms. Sedimentary strata. Hard cap rock. Mesa and scarp terrain. Stair step pattern. The most resistant limestone and sandstone are responsible for Mesa and scarp.
Mesa and scarp terrain
Eroded strata =
Inclined slopes
Resistant strata =
Mesa or scarps.
A flat topped steep sided hill w/a limited summit area. Remnant of former extended area. Sometimes in isolation. 3 Mesa
Smaller but related to a Mesa. Erosion all remnant. Very small surface area/cliffs rise above surroundings formed from mesa Mass wasting. 2
Further residual feature of butte, smaller “pinnacle” final aspire resistant cap-rock protects underlying beds. 1
Pillar
The top plat forms. bonded on one or more sides by escarpment, 4
Plateau
The loss of lands productivity, caused by human induced factors and climate Change. “Land degradation” climate change lead to drought. -deforestation -overgrazing livestock -improvident use f water resources. -dust bowls -a case of desertification -caused by imprudent land use and poor economic conditions .drought impacts -vegetation disappears live stick perishes 10-1000’s of people die outflow of uncertain futures to overcrowded areas
Desertification
