Deserts

Deserts

An area or region that lacks moisture, often exposing barren rock or sediment and hosting a hostile climate

Dry climate

The loss of evaporation is greater than water gained by precipitation

Steppes

Semi-arid, not as dry as deserts

Subtropical deserts

Under high pressure belt between H and F cells, the dry air flows down, unlike low pressure belts that have most air

Polar deserts

Similar to subtropical, in high pressure regions Mi

Mid latitude Rainshadow

Moist air from ocean rises between rhe mountain barrier, moisture condenses to form clouds and precipitate on the windward side, the desert is on the leeward side

Mid latitude Continental interior deserts

Moisture on air spent by the time the interior is reached, causing a desert

Atmospheric circulation

Can’t be vertical and uniform, because warma ir would rise and equator and cold air would sink at the poles. because of earth’s rotation, air flow is deflected because of CORIOLIS FORCE

Coriolis force

Leads to

• Hadley cells on either side of equator

• Polar cells centres at poles where cold air sinks\

• Ferrell cells between hadley and polar

Sediment transport

Similar to streamd, bedload at land surfce, suspended load in air can be carried long distances

Deflation

Winnowing: wind selectively picks up light/small particles and carries them away in suspension, desert payment formed and protects the underlying material

Blowouts

Shallow depressions, small patches of solid anchored by vegetation remain as humps/pillars

Abrasion

• Sediment carried can polish rock, VENTIFACTS are rocks that have been worn down smooth by sandblasting process

Aeolian deposits

Accumulation of wind-transported/deposited particles

Loess

Windblow silt/clay associated with arid and glaciation, thick accumulation

Sand

sand-sized particles of resistant minerals, commonly molded into dunes

Crossbedding Dunes

Many have an asymmetric profile, (gentle windward, steep leeward), sand transported up the windward side with saltation, and avalanches occur down the leeward side

Continued process causes

Migration downwind, inclined crossbedding patterns, and always slant down current

Type of dunes depends on

Sand supply, wind strength and speed, and the presence'/absence of vegetation

Barchan

Crescent shaped, tips point downwind, on level surfaces

Transverse

Ridge-like, perpendicular to wind direction where sand supply is high

Parabolic

Crscent points UPWIND, where land surface is stabilitzed by vegetation and the sand supply is high (blowouts between tips)