- Vertical rock strata (soft/hard) parallel to pr.
- Vertical rock strata (soft/hard) parallel to pr. wind DEFLATION HOLLOW - Large amounts of sand are removed by deflation leaving a hollow - Sand is removed by deflation and carried away in suspension by the wind. - From 3m wide and 1m deep to several kms wide and 100s of ms deep - May form due to faults in rocks ROCK PEDESTAL - More and more sand is removed until the surface is covered by closely packed rock fragments. - Some undercutting may occur depending on the angle of the rock strata hard - Shaped by deflation and wind abrasion - Horizontal rock strata (soft/hard) - 3 to 30m high - Joints in resistant rock widened by weathering - Abrasion cuts through resistant rock and develops deep furrows in softer rock underneath - Undercutting (abrasion and saltation)may occur like with a rock pedestal - May reach water table and produce an oasis or salt lake - Rocks are too large to be moved so get left behind - Up to 1000m long soft YARDANG - They may have more than one smoothed edge if there is more than one wind direction or they get moved by the wind. - 5 to 100m high ZEUGEN - They have sharp edges and smooth sides REG/DESERT PAVEMENT VENTIFACT
- Rocks lying on the desert floor that have been shaped by the wind (abrasion) - Mushroom shaped rocks - Abrasion undercuts a mass of resistant rock. - Less resistant layers will be eroded faster - The bottom is eroded more because it may be softer rock - Also abrasion is most effective Up to a height of 1.5m from the ground Desert Landforms Desert Landforms Fluvial Erosion Desert Landforms Aeolian Deposition MESA, BUTTE, SPIRE - Large areas of sand in arid regions are called ERGS - Barchan are a common type of dune resulting from wind deposition - Crescent shaped with horns facing downwind; horns move faster because less sand to move - Migrate up to 30m per year. Up to 30m high (but other dunes vary from few mm to 1000m). - Sand moved up windward slope by saltation and surface creep - Eddying wind helps maintain steep slopes on leeward slope - Continual avalanches on leeward slope - Coarsest grains are at the top - Bottom of leeward slope has sand ripples p.127 PEDIMENT BARCHAN DUNE Aeolian Erosion - Form in sedimentary rock with horizontal bedding planes. Mesa becomes a butte when it is taller than it is wide. - Lower slopes covered in scree from weathering and rockfall. Eroded by water. Good example of parallel retreat as the sides are eroded uniformly all over. - May have a resistant igneous cap rock. Steep slopes fall away to a wadi or canyon. Spire - Pediments are wide gently sloped regions at the base of more steeply sloped desert mountain ranges. - Often there is little or no soil on top of the bedrock - May be hidden by a bajada or alluvial fan - May be at the base of a Mesa/Butte INSELBERG
- Rounded isolated hill - Found in semi-arid regions as well as other climates Desert Landforms - Much debate about their formation Fluvial Deposition - Believed to be relic features formed when rainfall was high by deep chemical weathering - Crystalline rock e.g. granite SALT LAKE - Vary from a few ms in length to over 100km long - Water collects in deflation hollows and rapidly evaporates due to high temperatures - Capillary actions draws salts to the surface creating a thick crust, which cracks into polygonal shapes - Thick sediment leads to braiding - Sodium chloride is the most common salt. These salts may be commercially exploited. - Patterns change after each flood - Also known as Chotts or Playas - Found in semi-arid environments. - A stream exits the foot of a mountain meeting gentle lowland slopes - Steep sided with broad flat bottom - Soft and relatively impermeable rock is shaped by rapid runoff from heavy but irregular rainfall - Landscape comprises both erosional and depositional landforms e.g. wadis, pipes, arches, hoodoos, alluvial fans. ALLUVIAL FAN BADLANDS WADI - Dry river channels carved out by water erosion during flash floods/ ephemeral rivers. - Rapid energy loss leads to rapid deposition. - Deposits spread out in a fan shape - Material is graded with the coarsest load deposited first - Vary in size from a few ms to several kms in length
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