A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The process is called Volcanism and has been ongoing on Earth since the initial stages of its evolution over 4 billion years ago.
Types of Volcanoes
Volcanoes are segmented as per the style of eruption and the form which is created on the earth’s surface.
- Cinder cones are circular or oval cones made up of small fragments of lava from a single vent that have been blown up. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics that build up around the vent.
- Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own.
- These kinds of volcanoes are the largest of other volcanoes that are presently active on the surface of the Earth.
- These kinds of volcanoes are made up of basalt.
- They will become explosive in case water goes inside the vent. Else these volcanoes are being characterized by low explosivity.
- The lava that moves upside down does so in a fountain form and emanates the cone at the vent’s top before developing into a cinder cone.
- Composite Volcanoes occur due to the outbreaks of cooler and more viscous lavas than basalt.
- The occurrence of these volcanoes is mainly explosive eruptions.
- A huge amount of pyroclastic material and ashes easily gets wiped away with lava.
- The material is collected near the vent openings which in turn results in the creation of layers.
- Mayon Volcano, Philippines; Mount Fuji, Japan, etc. are the major composite volcanoes in the world that erupted in the past.
- Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent. They are built by slow eruptions of highly viscous lava.
- They are sometimes formed within the crater of a previous volcanic eruption. Like a composite volcano, they can produce violent, explosive eruptions, but their lava generally does not flow far from the originating vent.
Mid-Ocean Ridge Volcanoes
- These kinds of volcanoes mostly erupt in the oceanic areas.
- There exists a system of mid-ocean ridges that stretches to more than 70000 kilometres across the ocean basins.
- The central region of this ridge registers the maximum eruptions regularly.
Volcanism Lava types
- Magma is composed of molten rock and is stored in the Earth’s crust. Lava is magma that reaches the surface through a volcano vent.
Andesitic or Acidic or Composite or Stratovolcanic lava
- These lavas are highly viscous with a high melting point.
- They are light-coloured, of low density, and have a high percentage of silica.
- They flow slowly and seldom travel far before solidifying.
- The resultant volcanic cone is therefore stratified (hence the name strato volcano) and steep-sided.
- The rapid solidifying of lava in the vent obstructs the flow of the out-pouring lava, resulting in loud explosions, throwing out many volcanic bombs or pyroclasts.
- Sometimes the lavas are so viscous that they form a lava plug at the crater like that of Mt. Pelée in Martinique (an island in the Lesser Antilles, Caribbean Islands).
- Andesitic lava flow occurs mostly along the destructive boundaries (convergent boundaries).
Basic or Basaltic or Shield lava
- These are the hottest lavas, about 1,000 °C and are highly fluid.
- They are dark coloured basalt, rich in iron and magnesium but poor in silica.
- They flow out of volcanic vent quietly and are not very explosive.
- Due to their high fluidity, they flow readily with a speed of 10 to 30 miles per hour.
- They affect extensive areas, spreading out as thin sheets over great distances before they solidify.
- The resultant volcano is gently sloping with a wide diameter and forms a flattened shield or dome.
- Shield type lava flow is common along the constructive boundaries (divergent boundary).
- Volcanoes of the Mediterranean region are mainly associated with the Alpine folds, e.g. Vesuvius, Stromboli (Light House of the Mediterranean) and those of the Aegean islands.
- A few continue into Asia Minor (Mt. Ararat, Mt. Elbruz).
- The volcanism of this broad region is largely the result of convergence between the Eurasian Plate and the northward-moving African Plate.
- This type of volcanism is mainly due to breaking up of the Mediterranean plate into multiple plates due to the interaction of African and Eurasian plate
Extinct, Dormant and Active volcanoes
- Barren Island in the Andaman and Nicobar Islands, Anak Krakatoa are active volcanoes
- Mount Kilimanjaro (it has three volcanic cones), is a dormant stratovolcano in Tanzania.
- Mount Kenya is an extinct stratovolcano.
- The Barren Island in the Andaman and Nicobar Islands of India which was thought to be extinct erupted recently.
- Before a volcano becomes extinct, it passes through a waning stage during which steam and other hot gases and vapours are exhaled. These are known as fumaroles or solfataras.
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