3.1.2.2 systems + processes

• Geomorphological processes

  • Weathering
  • Mass movement
  • Erosion
  • Transportation
  • Deposition
• Weathering

  Breaking down of material in situ, where it is, doesn't include transportation, like erosion, produces regolith
• Mass movement


  Movement of material down slope with gravity + aided with water, dominated by rock falls as limited soil, small blocks of rock become detached from an exposed cliff, more likely if heavily jointed, debris flow - material flows downslope, during/ after rainfall = reduction in friction = material is more likely to collapse = saturated + heavy
• Erosion

  Wear away land via mechanical action, wind + water = denudation/ degradation of the earth, deflation - removal of fine loose particles from the grounds surface, creates a surface covered in concentration of coarse pebbles/ fine pebbles = desert pavement, abrasion - small particles being carried by the wind scrape particles from the rocks surface, sandpapering effect, attrition - desert occurs during transportation + small pebbled picked up by the wind = collide with each other + bits are broken = smaller pieces picked up by wind and undergo abrasion
• Transportation

  Move material from the site of erosion to deposition, suspension - small particles, are picked up and carried by the strongest wind, 0.15mm, remain airborne, dust storms = examples of manifestation of suspended particles in strong winds i.e loesses, saltation - small particles lifted + from ground and bounce along, 0.15mm-0.25mm, strong winds, surface creep - larger particles, pushed along the ground by particles moving through saltation, blown along floor, traction - larger stones/ boulders rolled along river bed, high energy/ river discharge, blown along floor, solution - transport of dissolved materials
• Deposition

  Reduction in energy = deposition, dependent on size of particle + energy of wind, 30% of all deserts = wind blown sand
• Arid Geomorphological processes

  • Weathering
  • Thermal fracture
  • Exfoliation
  • Chemical weathering
  • Block and granular disintegration
• Thermal fracture

  Huge diurnal range, extreme variations in temperature, rocks expand when hot during day, contract when cold at night, occurs at different rates, on different parts of rocks = fractures
• Exfoliation

  Breaking, splitting/ peeling of rock, as cracks form parallel to surface, saline water enters pores/ cracks of rocks, high temps = salt crystals = form and expand = exerting pressure on rocks, pressure changes in rocks, outerpart is very warm during the day, inside its relatively cooler, cools form the inside out
• Freeze thaw

  Large diurnal range, freeze, expands = pressure, breaks off
• Chemical weathering

  Rate is slow, crystal/ salt weathering = capillary action = crystal formation of water deposited in rocks = formation of larger crystals, increases pressure on rocks, hydrolysis/carbonation - mildly acidic water combines with mineral in rocks = clays/ dissolvable salts = weaker then parent rock, carbonic acid > calcium carbonate, oxidation - break down of rocks via oxygen - red brown colour, iron/manganese has been oxidised, causes desert varnish, hydration - small amounts of moisture/ dew on cold desert morning, combines with minerals + salt = swelling= pressure = cracks
• Block and granular disintegration


  Block - heavily jointed, constant heating + cooling + freeze that leads blocks to break off, granular - more granular structure, freeze thaw + differential thermal expansion, individual grains break off
• Sources of water

  • Exogenous
  • Endoreic
  • Ephemeral
  • Episodic role of water
  • Sheet flooding
  • Channel flooding
• Exogenous rivers

  Have source outside the desert margin + terminate at a sea = pass through desert, perennial + flow all year, despite evapo reducing their volume, include ground water + rivers = greatest volume of water flowing in deserts i.e river Nile which starts in ethiopa and mouth in Mediterranean sea
• Endoreic river

  Closed drainage basins, terminate inland in the form of an inland sea/delta/lakes/swamps i.e river Jordan terminates to form the Dead Sea
• Ephemeral river

  Rivers that flow on surface periodically, intermittently, seasonally = after heavy rainstorms/ torrential downpours, Snowmelt and episodic flash floods provide the water for these intermittent rivers and are also known as wadis
• Sheet flooding

  Sudden + intense torrential rain + impermeable baked surface + velocity + amount of rainfall + lack of vegetation = sheet floods, water flows evenly over land and is not confined to channels, impact of rain dislodges + moves loose material across the surface = sheet wash/ erosion, slow moving, even flow of water overland, flows down gentle slopes, transport pebbles, gravel + sand by suspension/ saltation, erodes desert surface by abrasion
• Channel flooding

  Flash flood, sudden strong, rapid flow of water through channel, heavy precipitation can't be absorbed by the dry soil, so runoff collects in channel and flows rapidly downhill, transport large loads of sediments and can be very powerful, due to concentration of water in narrow valley, creating a deep fast - flowing torrent if water, erodes the channel deeper via abrasion
• Rainfall is sporadic, however, rare substantial, intense flash floods generate considerable runoff
• Episodic flash floods arise from convectional storms in mountain ranges and flow as sheet floods or are confined within channels
• Despite being short-lived, large amounts of sediment are washed down from the mountains to be deposited on alluvial lowland plains
• There is a limited vegetative cover to absorb water and this limits humus levels, lowering plant root disturbance, making the soil dense and compact
• Rain is therefore, able to beat down on the surface with maximum impact, dislodging fine particles and blocking pore spaces, thereby further reducing the infiltration rate
• Water's effectiveness in erosion, is due to factors such as vegetation cover, slopes and the permeability of surfaces as well as rainfall amounts
• Many desert landforms may be relict features, formed during wetter climatic periods
• Deposition

  Takes place when velocity drops, usually on the inside of meander bends and where streams/channels flow out of the mountain edges onto flat desert plains
• Types of water erosion

  Rills,

  gullys,

  bank erosion - fast flowing water erodes sides + undercuts channel bank = bank collapses + widening of channels