VULCANICITY

A volcano is an opening in the crust of the earth, connected by a conduit to an underlying magma chamber, from which molten lava, volcanic gases, steam, and pyroclastic materials are ejected. It is usually in the form of a peak which may be cone shaped or dome-shaped depending on the type of volcano and type of material ejected. The main causes of volcanic eruptions are associated with sea-floor spreading, plate-tectonics and mountain building processes.

At present, the only active volcanoes in India are at the Barren and Narcondom Islands (Andaman group of Islands), but geographical evidence is available for vulcanicity in the past. Prof. ILL. Clubber (1945) has identified six areas of vulcanicity in the country which are given as follows:

Fig. 2.25 India—Seismic Zones

1. The Dharwar Vulcanicity: Traces of basalt deposits are found in the form of D alma Trap in Jharkhand.

2. Cuddapah Vulcanicity: This occupies Cuddapah, Bijapur and Gwalior areas.

3. Vindhyan Vulcanicity: Its evidences are found in the Malani (Jodhpur) and Kirana (Punjan) Hills in Rajasthan.

4. Palaeozoic Vulcanicity: During this phase, volcanic eruptions were noticed in Kashmir and Himachal Pradesh. Traces of volcanic deposits have been found in Pir Panjal Range, Dalhousie (II.P.), Bhuwali, Bhimtal, and Saugaon (Kumaun-Uttarakhand).

5. Mesozoic Vulcanicity: During this period, volcanic eruption took place in Rajmahal Hills (Jharkhand) and Abor Hills of Arunachal Pradesh.

6. The Cretaceous Vulcanicity: During this period, enormous quantity of basalt upwelled through fissure eruptions over the north-western part of the Peninsula, forming the Deccan Trap.

Geologists opine that apart from the Barren Islands, volcanic activity is going on beneath the Himalayan crust due to the subduction and melting of the northern margin of the Indian Plate.

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