Theory question 203
Wind and Desert LandformsWith the aid of diagrams, describe the characteristic and mode of formation of any two of the following: (a) Rock pedestal (b) Yardang (c) Mesa
Show the model answer
Rock pedestal: diagram of a mushroom-shaped rock with narrow base. Formed in deserts where wind carries sand close to the ground and abrades the lower part more (sandblasting); softer lower layers wear faster; top stays wide.
Yardang: diagram of ridges and furrows along the wind direction. Formed where vertical bands of hard and soft rock lie parallel to the prevailing wind; soft bands are scoured into furrows, hard bands remain as steep-sided ridges (several metres high).
Mesa: diagram of flat-topped hill with resistant cap rock and steep sides. Formed where horizontal layers have a hard cap over softer rock; erosion by water and wind wears back the sides, leaving a broad table-like hill; further erosion produces a smaller butte.
Each feature needs a labelled diagram plus how it forms.