Desert Landforms

Desert Landforms

1. Landforms associated with wind action

   • Yardang
     • they are narrow, streamlined ridges that are usually 3 to 4 times longer than they are wide.
     • Strong prevailing winds blowing in one direction, carry sand in suspension, which erodes rocks by abrasion.
       • softer rock is eroded faster than harder rock, so ridges of hard rock are created. The ridges aren't always continuous.
   • Zeygen
     • They are long, block-shaped ridges of rock. Zeygens are typically made out of sedimentary rocks - e.g. sand stone and are laid down in horizontal layers.
     • They're formed in areas where a layer of hard rock sits above a layer of soft rock.
       • if cracks form in the hard rock due to weathering processes such as host shattering, the wind can erode through the cracks and into the softer rock beneath by abrasion.
         • Again, the softer rock is eroded more than the hard rock, and ridges are formed.
     • Water erosion and weathering are also active in forming a zeygen.
   • Sand Dunes
     • They form when sand grains carried by suspension are deposited as the wind slows down.
       • Vegetation, rocks and other dunes slow wind down, causing it to drop its load.
         • Shape and Layout is affected by several factors - speed, direction and consistency of the wind, the amount of sand beiing transported, the nature of the ground surface, the amount and type of vegetation.
     • Barchan Dunes
       • Crescent - shaped isolated dunes that develop from mounds of sands. they form in the direction of the prevailing wind as sand is deposited.
         • When the slope of the dune becomes too steep, sand avalanches occur, depositing sand at the base (downwind).
           • Swirling wind currents (eddies) help to keep the slope deep. The dune slowly moves forward in the direction of the wind.
             • If there's a lot of sand being deposited, many barchan dunes connect with each other to form a barchanoid ridge.
     • Seif Dunes
       • they are longitudinal, elongated sand dunes and form from barchan dunes if a change of wind direction occurs.
         • When the wind changes direction, it causes on of the horns to lengthen. Over a period of time, the wind alternates between X and Y and the horn becomes longer.
           • As the wind direction continues to alternate, the dunes is steadily transformed into a longitudinal or self dune.

2. Landforms assoiciated with water

   • Wadis
     • a gully, are steep-sided, dry river valleys eroded by seasonal rivers e.g. the Grand canyon.
     • They are formed by river erosion, when occasional high-discharge events like flash floods wash out sediment from the surrounding mountains.
       • The sediment washed out through a wadi is deposited at the base of its mountain range, forming a delta - like ALLUVIAL FAN.
         • A the water spreads out at the mouth of the wadi, energy is lost and sediment is rapidly deposited. Over time as water re works this vast store of sediment, the alluvial fan displays clear sorting patterns.
   • Mesas
     • are large plateau like features, often bordered by steep Wadis or canyons.
     • They are isolated, and are only found in arid areas and are composed of a hard horizontal layer.
     • Buttes
       • are small pinnacles of rock, and are smaller and narrower versions of mesas.
     • water washes smaller and softer types of rocks away from the top of a hill. The strong, durable rock that remains on top of a mesa is called caprock. A mesa is usually wider than it is tall.