IB Geography C.2.3 Weathering and Erosion in Hot Arid Environments Notes

Aridity Changes the Balance of Weathering

1. Hot arid environments receive little and unreliable rainfall, experience strong evaporation and often have sparse vegetation that leaves rock and sediment exposed.
2. Physical weathering is often prominent because large daily temperature ranges, salt crystallization and occasional freezing apply stress to rock without requiring continuous moisture.
3. Chemical weathering is slower where water is scarce but becomes important after rainfall, along shaded joints or where groundwater brings dissolved salts into contact with rock.

Physical Weathering Produces Loose Debris

1. Thermal stress develops as exposed rock surfaces heat and cool more quickly than their interiors, encouraging cracking where minerals expand at different rates.
2. Salt weathering occurs when saline water enters pores and crystals grow during evaporation, exerting pressure that breaks grains from the rock.
3. Wetting and drying can make clay-rich rocks expand and contract, weakening surfaces that are repeatedly exposed to brief rainfall and intense drying.
4. These processes are most effective where rock properties, moisture pathways and repeated cycles allow stress to accumulate.

Wind Erodes, Transports and Sorts Sediment

1. Deflation removes loose fine particles and may leave a lag deposit of coarser stones known as desert pavement.

1. Wind abrasion occurs when saltating sand strikes exposed rock, with the greatest impact near the ground where the sand load is concentrated.
2. Fine dust travels in suspension, sand moves mainly by saltation and larger grains creep or roll along the surface.
3. Wind loses competence when velocity falls or an obstacle creates shelter, causing deposition and sorting sediment by size.

Flash Floods Perform Most Fluvial Work

1. Dry soils, crusted surfaces and sparse vegetation can produce rapid overland flow when intense rain exceeds infiltration capacity.
2. A flash flood has high erosive power because discharge and velocity rise quickly within normally dry channels.
3. Water transports dissolved load, suspended sediment, saltating particles and larger bedload until declining velocity forces deposition.
4. Sediment is commonly deposited where a confined channel leaves a mountain front and spreads across a gentler plain.

Wind and Water Rework the Same Sediment

1. Flash floods may deliver sand and silt to valley floors, after which wind redistributes the dry sediment into dunes or removes dust from the basin.
2. A desert landform therefore often records alternating fluvial and aeolian processes rather than one agent acting alone.
3. Relative process importance varies with rainfall intensity, sediment supply, vegetation cover, wind regime and distance from source areas.