Theory question 205
Earth Movements and VulcanicityWith the aid of diagrams and examples, write explanatory notes on any two of the following: (a) Rift valley (b) Horst (c) Volcanic mountain.
Show the model answer
(a) Rift valley: a long narrow valley with steep sides formed when a block of land sinks between two parallel normal faults (tensional forces), or when compression pushes side blocks up; diagram of the sunken block between faults; e.g. East African Rift Valley, Rhine rift valley, Jordan valley.
(b) Horst (block mountain): an upstanding block between two parallel faults, formed when the side blocks sink or the centre is pushed up; steep sides and a flat top; e.g. Ruwenzori, Vosges, Black Forest, Usambara.
(c) Volcanic mountain: formed when magma and other materials pour out through a vent and pile up into a cone; may be an ash cone, lava cone or composite cone with crater at the top; e.g. Mount Cameroon, Kilimanjaro, Fuji.
Draw a labelled cross-section for each feature.