Theory question 204
Earth Movements and Vulcanicity(a) Describe the characteristics of any two of the following types of landforms (i) delta (ii) atoll (iii) caldera
(b) Explain with the aid of diagrams the mode of formation of each of the landforms you have chosen
Show the model answer
Any two:
Delta – (a) low, flat, fan/triangular plain of alluvium at a river mouth; river splits into distributaries; swamps, lagoons, sandbars; (b) river slows on entering a calm, shallow sea and deposits its load; needs heavy load, tideless/sheltered coast, no strong currents; layers build seaward (diagram)
Atoll – (a) ring-shaped coral reef enclosing a lagoon, low islands on the reef; (b) coral grows round a volcanic island in warm, clear, shallow sea; island subsides or sea level rises while coral grows upward, leaving a ring reef (fringing → barrier → atoll diagrams)
Caldera – (a) very large basin-shaped depression at the top of a volcano with steep walls, often holding a crater lake; (b) violent explosion blows off the top of the cone, or the summit collapses into the emptied magma chamber (diagram)
Each formation needs a labelled diagram.