There are about 500 volcanoes which are either active or have been active in historical times.
Volcanic material comes out from weaker sections of the surface. There appears to be a close relationship between the weaker sections and the site of mountain areas.
(1) Island Festoons of the Pacific. Two-third of world's active volcanoes and thousands of inactive volcanoes are found in this belt. The volcanic belt surrounds the Pacific Ocean. It is also known as Circle of Fire. Among the important volcanic areas of this circle of fire are Aleutian Islands, Alaskan Sub-continent, Guatemala, northern and southern Andes. This circle of fire makes contact with the Atlantic belt at two places.
(2) Alpine-Himalayan belt. Volcanoes are not large in number in this belt. The belt starts from Madeira and the Canary Islands and passes through the Vesuvius, the Etna and the Aegean volcanoes of the Mediterranean Sea. The belt continues further through Caucasus (Elburz), Armenia (Ararat), and reaches Balochistan. After crossing the Himalayas the belt crosses Burma, Andamans and probably ends in Indonesian Islands. Volcanoes at some places in this belt are very close. Tibet is free from volcanoes.
(3) African Rift Valley. This starts from the Bay of Guinea to Red Sea passing through the middle of Africa. The most active volcano in this belt is Tanzania's Mt. Kilimanjaro. Kenyan volcanic mountains are beyond this rift valley, but Algon is within this belt.
(4) Other Volcanic Areas. Some volcanoes are situated in Mid-Atlantic. Cape Verde is famous among them. Azores, St. Helena, and Ascencion are volcanic islands but they are mostly inactive. The place where the ridge starting from Britain to Greenland meets the above-mentioned belt, has very active volcanoes. For example, Iceland has more than 20 active volcanoes.
Classification of Volcanoes. Volcanoes are classified on various bases. On the bases of activity volcanoes are of three types: active volcanoes, dormant volcanoes and extinct volcanoes. There is also a classification Based upon Exploded and Ejected Material. See next page.
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