hot and arid environments

• Aridity is when there is a lack of moisture, especially having insufficient rainfall to support trees and plants
• Global distribution of arid areas

  Most are located in tropics

  Some located next to cold ocean currents

  Continental interiors

  lee of mountain ranges
• Rainfall in semi arid areas

  250-500 mm
• Rainfall in arid areas

  125 - 250 mm
• rainfall in extremely arid areas

  less than 125mm
• 4 causes of aridity

  • Continentality
  • Subtropical high-pressure belt
  • Rainshadow effect
  • cold offshore currents
• How does subtropical high pressure cause aridity

  • Hot and dry air descends, preventing rising air from reaching any great heights
  • Therefore there will not be enough condensation
  • As the hot air sinks, it will also spread out, preventing marine air from entering the region
  • this occurs at 20-30 degrees latitude
• How does continentality cause aridity

  • Distance from the sea
  • only a limited amount of water can be carried by the wind
  • therefore arid regions are found far away from bodies of water
• How does rain shadow cause aridity

  • as air rises over mountains, it cools
  • this causes the moisture to condense and fall as precipitation, meaning that the other side will receive no rainfall
  • relief rainfall
• How do cold offshore currents cause aridity

  • air moving from oceans is cooler, therefore holds less moisture
• 4 features of arid regions

  • High wind speeds
  • High evapotranspiration
  • very Low rainfall
  • temperatures vary seasonally and diurnally
• 7 weathering processes in arid regions (4 mechanical, 2 Chemical)

  • Freeze-Thaw
  • Thermal Fracture (Exfoliation)
  • Granular Disintegration
  • Block Separation
  • Solution
  • Hydrolis (Hydration)
  • Salt Weathering
• What is Freeze thaw

  • Water is stuck in joints and cracks
  • freezes at 0 degrees due to diurnal temperature changes
  • expands by around 10 percent
  • continual repetition of this results in cracking of rock
• what is thermal fracture

  • similar to exfoliation
  • during the day, the hot rock expands, and at night they contract, setting up stresses in the rock
  • Eventually, the outer layer will flake off due to expanding and contracting at a faster rate
• What is granular disintegration

  • certain grains in the rock are more prone to expansion than others
  • therefore, this exerts greater pressures on the grains surrounding them, forcing them to fall off
• what is block separation

  • splitting of rocks along their joints into blocks
  • internal heating of the rock will cause these to fall off
• What is solution

  removal of the rock by acidic rainwater
• What is hydrolis (hydration)

  certain minerals absorb water, expand and change
• what is salt weathering

  • high temperatures draw saline groundwater to the surface of the rocks
  • evaporation of this water leaves behind salt crystals
  • these grow over time, causing stresses and cracking the rock
• 2 types of erosion in arid environments

  Abrasion

  • Particles are driven against rocks, wearing away at them

  Deflation

  • loose regolith is removed by the wind, leaving larger materials such as stones