Thursday, October 29, 2009


VOLCANIC LANDFORMS There are several landforms that are associated with volcanoes. Important among them include:

Batholith Batholith or bathylith is a very large dome­shaped intrusion of magma, typically several kilometres in depth and extending over hundreds of square kilometres. It is usually composed of acid rocks, such as granite and diorite, and is always associated with an area where mountain-building has taken place. Examples of batholiths include Dartmoor, Devon, and the Moume Mountains in Northern Ireland.

Laccolith Laccolith or laccolite is a large dome-like mass of igneous rock (magma) that was intruded along a bedding plane in a sedimentary sequence of rocks. In the well-developed laccoliths, the base tends to be relatively flat so that the resulting intrusion has a lens shape. When a number of laccoliths are stacked one above another from a single intrusion, they are termed a cedar-tree laccolith.

Sill Sill is a horizontal intrusion of magma along a bedding plane between two rock layers. When cooled, magma forms a -tabular sheet more or less parallel to the surrounding layers of rock. The best known example in the British Isles is the Great Whin Sill in Northern England which is composed of dolerite.
Dyke When a mass of magma cuts across the bedding planes and forms a wall-like structure, it is termed a dyke. Dykes tend to occur in large numbers, known as swarms, e.g., on. the coast of Isle of Arran, and on the Isle of Mull, Scotland. Some dykes when exposed on the surface, stand as ridges or escarpments. In ridges, the side with gentle slope is termed dip, while the side with steeper slope is termed scarp.

Hot Spring Hot or thermal spring is a spring of hot water that flows out of the ground heated by volcanic areas, e.g., at Bath, Avon. The water that flows from hot springs often contains a large proportion of dissolved minerals, which may be deposited as basins or terraces around the hot springs. Iceland and New Zealand have thousands of hot springs.

Geysers Geysers are fountains of hot water and super­heated steam that may spout up to a height of 150 feet from the earth beneath. The phenomena are associated with a thermal or volcanic region in which the water below is being heated beyond boiling point. Almost all the world's geysers are confined to three major areas; Iceland, the Rotorua district of North Island (New Zealand), and Yellowstone Park of USA. The world's best known geyser is perhaps 'Old Faithful' in Yellowstone National Park, Wyoming, which erupts at regular intervals - every 63 minutes on the average. In 1904, the Waimangu Geyser in New Zealand erupted to a height of about 457 m, higher than the world's tallest building, the Sears Tower (445 m) in Chicago.

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