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
