Theory question 204
Wind and Desert LandformsWith the aid of diagrams, describe the appearance and mode of formation of any two of the following landforms: (a) Delta; (b) block mountain; (c) rock pedestal.
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(a) Delta: a low, flat, roughly triangular or fan-shaped plain of alluvium at a river mouth, crossed by many distributaries, with swamps, creeks and lagoons; forms where a river enters a sea or lake, slows down and drops its load faster than waves and currents can remove it, helped by a gentle offshore slope and sheltered coast; types arcuate (Niger, Nile), bird's foot (Mississippi), estuarine.
(b) Block mountain (horst): a raised block with steep fault-scarp sides and a fairly flat top; formed when the land between two parallel faults is pushed up, or the land on both sides sinks, through tension or compression, e.g. Vosges, Black Forest, Ruwenzori, Usambara.
(c) Rock pedestal (mushroom rock): a rock with a narrow base and a wide cap; formed in deserts where wind carrying sand blasts (abrades) the lower part of a rock most strongly because sand is heaviest near the ground; softer bands are cut back faster, leaving a top-heavy pillar.
Draw each landform and label its parts.