Question 20 of 21: Question 7, Part 2: Define Terms

Question 7, Part 2: Define Terms (8 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

a) Loess. A blanket deposit of wind-blown (aeolian), fine, well-sorted silt-sized sediment, typically derived from glacial outwash plains or deserts; loess is unstratified and sufficiently cohesive (bound by thin clay/carbonate coatings) to stand in steep, even vertical, faces without collapsing.

b) Crescent (barchan) dune. A crescent-shaped sand dune whose "horns" point downwind, formed where sand supply is relatively limited and wind direction is fairly constant and unidirectional – sand is pushed up the gentle windward slope and avalanches down the steeper leeward slip face, migrating the dune downwind over time.

c) Wave-cut platform. A gently sloping, flat rock bench eroded at the base of a sea cliff by wave abrasion and hydraulic action; as the cliff retreats landward under continued wave attack, the platform widens, typically remaining at approximately the level of low tide.

d) Deflation. The removal and lifting of loose, fine-grained (silt/clay/sand- sized) sediment from a land surface by wind, which winnows away the finer fraction and can lower the surface (forming deflation hollows/blowouts) while leaving a coarser lag of pebbles behind (desert pavement).