VOLCANIC LANDFORMS

Materials ejecting out from a volcano create a variety of land forms.

Ash or Cinder Cone. The volcanic material thrown out by volcano cools down quickly in small solid pieces known as cinders. The solid particles are rained down and form a circular cone around the crater. This cone is called cinder cone. The cinder cone is formed after a number of explosions. The average height of a cinder cone is about 300 meters and its side have concave slope. They are termed as central type of volcanoes because eruption takes place through a central hole in the crust connected with the interior through a vertical pipe.

Acid Lava Cone or Dome. This cone is formed by acid lava which is viscous and has the dominance of Silica. The lava deposits itself near the neck immediately after explosion and form a dome after solidification Lessen Peak in California and Pary-de-done in France are some of the outstanding examples of domes.

Basic Lava Cone or Lava Shield. Sometimes, the basaltic lava having low silica content flows out quietly and gives rise to the formation of a shield. The lava flows out quietly around a central opening. In course of time, it builds up a shield-shaped volcano with a wide base and low slope. It cools as thin horizontal sheets. Probably the best examples are the Mauna Lao shield volcanoes of the Hawaiian Islands.

Composite Cone. These are probably the largest and highest volcanic cones. They are formed by lava ash etc. which are deposited one after the other in almost parallel layers. Sometimes the main cone is covered by a number of smaller cones.

Caldera. Caldera is a large roughly circular volcanic depressions often several hundred square kilometer’s in area. Caldera usually has a number of smaller vents and can also contain a large crater lake. The distinction between craters and calderas is essentially one of size, one to kilometers being the lower limit for the diameter of a caldera. Calderas are formed in a variety of ways, but most accepted mechanism is the collapse or subsidence which may relate to explosive eruptions. There are numerous ex of caldera in Alaska and Aleutian Islands.

VOLCANIC PLUG. Volcanic plug is formed by the solidification of lava in the vent of the volcano after eruption is over. The plug becomes clearly visible after the erosion of the upper rock material. Such volcanic plugs are found in large number in the Hawaiian Islands. Sometimes it is called volcanic neck also. It can have 300 to 600 meter radius. The Devil Tower in Wyoming is the best ex of a volcanic neck.