In this post we will discuss about the volcanoes types and forms. So lets begin……

Types of Volcano

Volcanoes are given different name based on the periodicity of eruption, nature of eruption and the form developed at the surface.

Based on periodicity:

Active Volcano

Basically, active volcanoes have erupted in the past and are likely to frequently erupt.

Example: Stromboli of Lipari island

Dormant Volcano

These are active volcanoes that are not erupting but may do so in future.

Example: Barren Island in Andaman

Extinct Volcano

Extinct volcanoes are those where there has been no indication of past or future eruption. But they retain the features of a volcano.

Example: Mount Kenya in Kenya

Based on type of eruption:

Shield Volcanoes

These are the largest of all the volcanoes on the earth.

They are mostly made up of basalt, a type of lava that is very fluid when erupted. They form lava domes.

These volcanoes are not steep.

They are characterized by low explosivity. They becomes explosive only if somehow water gets into the vent.

Upcoming lava moves in the form of a fountain.They throw out the cone at the top of the vent and develops into cinder cone.

Example: Hawaiian volcanoes

Composite Volcanoes

They are characterized by eruptions of cooler and more viscous lavas than basalt.

These generally result in explosive eruptions.

Along with lava, large quantities of pyroclastic material and ashes find their way to the ground. Materials accumulates in the vicinity of the vent openings. This leads to the formation of layers, and this makes the mounts appear as composite volcanoes.

Craters and Caldera

These are most explosive of the earth’s volcanoes.

When they erupt, they tend to collapse on themselves rather than building any tall structure. Collapsed depressions are called calderas.

The magma chamber supplying the lava huge and in close vicinity.

Flood Basalt Provinces

They outpour highly fluid lava. These lava flows for long distances.

Example: Deccan Traps from India

Mid-Ocean Ridge Volcanoes

These are volcanoes occurring in the oceanic areas.

Central portion of this ridge experiences frequent eruptions.

Based on the form developed at the surface

Intrusive Forms

Lava that is released during volcanic eruptions on cooling develops into igneous rocks.

If igneous rocks cools at the surface, it is called volcanic rocks. If igneous rocks cools on the crust, it is called plutonic rocks.

The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.

Batholiths

Large body of magmatic material cools in the deeper depth of the crust. It develops in the form of large domes.

They appear on the surface only after the denudational processes remove the overlying materials. These are granitic bodies.

Batholiths are these cooled portion of magma chambers.

Lacoliths

These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below.

It resembles the surface volcanic domes of composite volcano but are located at deeper depths.

They are regarded as the localized source of lava that finds its way to the surface.

Example: Henry Mountains in Utah, USA

Karnataka plateau is spotted with domal hills of granite rocks. Most of these, now exfoliated, are examples of lacoliths or batholiths.

Lapolith, Phacolith and Sills

As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.  It may get rested in different forms.

In case it develops into a saucer shape, concave to the sky body, it is called lapolith.

Example: Bushveld lapolith, Transvaal, South Africa.

Wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country. Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.

Example: Corndon Hill, Shropshire England.

Batholith is a huge mass of igneous rocks, usually granite, which after removal of the overlying rocks forms a massive and resistant upland region.

Example:  Wicklow Mountains of Ireland.

Near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material.  The thinner ones are called sheets while the thick horizontal deposits are called sills.

Dykes

As we know, lava makes its way through cracks and the fissures developed in the land. It solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes.

Found in: Western Maharashtra area

Dykes are considered the feeders for the eruptions that led to the development of the Deccan traps.

Other Types

Hawaiian Types:

They erupt quietly due to less viscous lava and non-violent natures of gases.

They emit long glossy threads of red molten lava known as peel’s hair.

Example: Hawaiian Island.

Strombolian Type:

Their eruptions are almost rhythmic or nearly continuous in nature

Sometimes they are interrupted by long intervals.

Example: Stromboli volcano of Lipari island.

Vulcanian Type

They erupt with great force and intensity

The Lava is so viscous and pasty that these are quickly solidified.

Example: Mt. Vulcano of Lipari Island of Mediterranean Sea

Peleean Type

They are the most violent and most explosive type of volcanoes, named as Nuee Ardente (cloud of gas, ash and lava).

Example: Pelee volcano of Martinique Island in the Caribbean Sea

Visuvian type:

These are extremely violent and enormous in nature. Large volume of gases and ashes forms which clouds like cauliflower.

Fissure eruption type:

These are large quantities of lava that quietly well up from fissure. They, then spread out over the surrounding countryside.

Successive lava flows results in the growth of a lava platform.

Example: Deccan, Java island

Cinder:

Cinder are formed from volcanic dust, ashes and pyroclastic matter.

Its formation takes place due to accumulation of finer particles around the volcanoes vent.

Composite cones:

These cones are build by several eruptions of lava, ashes, etc. from the main conduit. Each new eruptions adds new layers of ashes or lava to the sides of the volcano.  This readily grows in height.

They are often called strato volcanoes.

Parasite cones:

From the main conduit, when lava comes out of the subsidiary pipes/dykes, parasite cones are formed.

Example: Mount Etna in Sicily

Lava domes:

These are formed due to accumulation of solidified lavas around the volcanic vents.

Lava plugs:

They are formed due to plugging of volcanic pipes and vents when volcano becomes extinct.

Craters:

During an eruption material from the top of the cone is blown off or collapses into the vent. This widens the orifice into a large depression. This depression is forming at the mouth of a volcanic vent is called a crater.

When it is filled with water, it becomes a ‘crater lake’

Example:  Lake Lonar in Maharashtra.

Calderas:

Generally, enlarged form of craters is called caldera. It is formed due to subsidence of a crater.

Geysers:

They are fountains of hot water and superheated steam that may spout from beneath the earth.

Example: Yellowstone Park of USA

Hot springs:

They are also called thermal spring. They may be found in any part of the earth where water sinks deep enough. This is mainly beneath the surface so that it can be heated by the interior forces. The water then rises to the surface without any explosion.

Example: Iceland

Fumaroles:

It is a vent through which there is emission of gases and water vapour.

Cryptodomes:

When viscous lava forces its way up, cryptodomes are formed. As a result, this causes a bulge.

Example: 1980 eruption of Mount St. Helens.

Super volcano:

These are volcanoes that usually have a large caldera. They can potentially produce devastation on an enormous, sometimes continental, scale.

Such eruptions can cause severe cooling of global temperatures for many years afterwards. This is mainly because of the huge volumes of sulphur and ash erupted. They are the most dangerous type of volcano.

Large igneous provinces are also considered super volcanoes. This is  because of the vast amount of basalt lava erupted, however they are non-explosive.

Examples: Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico