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A volcano is a vent or a group of closely spaced vents through which molted rocks magma and hot gases come out of deep seated sources. It has three important parts.

(i) Vents. The hot rock material and gases come out of a zigzag hole. This hole is known as vent.

(ii) Cone. The ejected rock material rushing out of the vent creates a cone like formation at the upper end of the vent. The cone has a steep slope and sometimes takes the form of a mountain.

(iii) Crater. A mouth opens at the upper peak of the cone. Molten material is ejected from this mouth. This mouth is funnel shaped. Its walls are almost vertical and are known as crater. Large sized craters are called camera. The diameter of a crater measure a few km.

Calderas, as mentioned, are circular in form and have circular but vertical walls. When the volcanoes are dormant, water accumulates in them and a lake is formed. These lakes are known as crater lakes. A crater called La Caldera situated in Canary Island has a diameter of 4.8 ton. It is surrounded by mountain walls about 4825 meters high. Among the Calderas of Hawaii, Kilauea and Mauna Loa are worth mentioning.

Material Ejected from a Volcano

In average a volcano in an explosion ejects 150 cubic km of material. In millions of years the ejected material becomes tremendous. The largest volcanic island among the Hawaiian group of islands has a volume of one hundred thousand cubic km when measured above the sea level.

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