Theory question 306
Earth Movements and Vulcanicity(a) What is volcanic intrusion? (b) Describe the characteristics and mode of formation of a block mountain. (c) List three landforms that are associated with intrusive volcanic activities.
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Model answer
(a) Volcanic intrusion is the forcing of magma into the rocks of the earth's crust, where it cools and solidifies below the surface.
(b) Characteristics: steep sides (fault scarps); flat or gently sloping top; bounded by faults; e.g. Vosges, Black Forest, Ruwenzori. Formation: tension or compression in the crust produces two parallel faults; the block between them is pushed up, or the land on both sides sinks, leaving the middle block standing as a horst (block mountain).
(c) Batholith; laccolith; dyke; sill; lopolith; phacolith.
Explanation
Mention the parallel faults.