Volcanoes, Vulcanicity and Landforms

What is the Volcanoes or Vulcanicity?

The term volcanoes, mechanism of volcanoes and vulcanicity are more or less synonymous.

‘A volcano is a vent, or opening, usually circular in form, through which heated materials consisting of gases, water, liquid lava and fragments of rocks are ejected from the highly heated interior to the surface of the earth.’

On the other hand ‘the term vulcanicity covers all those processes in which molten rock material or magma rises into the crust or is poured out on its surface, there to solidify as a crystalline or semicrystalline rock.’


Volcanoes of explosive type or central eruption type are associated with the accumulated volcanic materials in the form of cones which are called as volcanic cone.

There is a vent or opening ,of circular or nearly circular shape, almost in the centre of the summital part of the cone. This vent is called as Volcanic vent.

Volcanic mouth which is connected with the interior part of the earth by a narrow pipe which is called as volcanic pipe.

The enlarged form of the volcanic vent is known as volcanic crater and caldera.


Classification on the basis of the mode of eruption

Central eruption type or explosive

Hawaiian type

Such volcanoes erupt quietly due to less viscous lava and non violent nature of gases.

Rounded blister of hot and glowing mass of lava when caught by a strong wind glide in the air like red and glowing hairs. The Hawaiian people consider these long glassy threads of red molten lava as Pele’s hair.

Hawaiian eruptions get their names from the Kilauea volcano on the Big Island of Hawaii, which is famous for producing spectacular fire fountains. Two excellent examples of these are the 1969-1974 Mauna Ulu eruption on the volcano's flank, and the 1959 eruption of the Kilauea Iki Crater at the summit of Kilauea.

Strombolian type

Such volcanoes, named after Stromboli volcano of Lipari island in the Mediterranean sea, erupt with moderate intensity

Beside lava other volcanic materials like pumice, scoria bombs etc. are also ejected upto greater height in the sky.

The eruptions are almost rhythmic or nearly continuous in nature but sometimes they are interrupted by long interval.

Vulcanian type

These are named after volcano of Lipari island in the Mediterranean sea.

Such volcanoes erupt with great force and intensity.

The lavas are so viscous and pasty that these are quickly solidified and hardened between two eruptions and they crust over the volcanic vent.

These lava crusts obstruct the escape of violent gases during next eruption.

The violent gases break and shatter the lava crusts into angular fragment and appear in the sky as ash-laden volcanic clouds of dark and often black colour assuming a cauliflower shape.

Pleean type

These are named after the pelee volcano of Martinique Island in the Caribbean sea.

These are the most violent and most explosive type of volcanoes.

Ejected lavas are most viscous and pasty. obstructive domes of lava are formed above the conduits of the volcanoes.

Thus every successive eruption has to blow off these lava domes.

The most disastrous volcanic eruption of Mount Pelee on May, 1902 destroyed the whole of the town of St. Pierre killing all the 28,000 inhabitants leaving behind only two survivors to mourn the sad demise of their brethren.

Visuvious type

These are more or less similar to vulcanian and strombolian types of volcanoes, the difference lies only in the intensity of expulsion of lavas and gases.

There is extremely violent expulsion of magma due to enormous volume of explosive gases.

Volcanic materials are thrown up to greater height in the sky.

The ejected enormous volume of gases and ashes forms thick clouds of cauliflower form.

Such type of eruption was first observed by Plini in 79 A.D.

Fissure eruption type

Such volcanoes occur along a long fracture, fault and fissure and there is slow upwelling of magma from below and the resultant lavas spread over the ground surface.

Classification on the basis of periodicity of eruptions

Active volcanoes

These are those which constantly eject volcanic lavas, gases, ashes and fragmental materials.

There are about more than 500 volcanoes in the world.

Etna and Stromboli volcano are the most significant example of this type.

Dormant volcanoes

These are those which become quiet after their eruption for sometimes and there are no indication of future eruption but suddenly they erupt very violently and cause enormous damage to human health and wealth.

Visuvious volcano is the best example of dormant volcano.

Extinct volcanoes

These are considered extinct when there are no indications of future eruption.

Mt. Popo of Myanmar is the best example of this type.

This article is shared by Priyanka Duta. Priyanka is a Guest Lecturer of Geography at New Alipore College, Kolkata.

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