On the basis of activity:
Active Volcano: An active volcano erupts continuously in the present time. Example: Barren Island volcano at Andaman Nicobar Islands in India is the only active volcano of India. There are around 700 active volcanoes in the world, many under the sea. Stromboli in Italy or the ‘Lighthouse of the Mediterranean’ is one of the most active volcanoes on Earth.
Dormant or sleeping volcanoes: These are the most dangerous volcanoes in the world. Sleeping volcanoes do not have any fixed time of eruption , they can erupt any time. Example-Mt. Kilimanjaro ( Tanzania).
Extinct Volcano: An extinct volcano is the one which has not erupted for the last 10,000 years and is a dead volcano according to scientists. An extinct volcano has no lava supply in its magma chamber. Example- Mt. Thielson in Oregon USA is a dead volcano because it had last erupted 2,50,000 years ago.
On the basis of structure:
- Shield Volcano:
Shield volcanoes are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that of a warrior’s shield.
They are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great distances, and then cool as thin, gently dipping sheets.
Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone.
Some of the largest volcanoes in the world are shield volcanoes.
The Hawaiian Islands are composed of linear chains of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii— two of the world’s most active volcanoes. The floor of the ocean is more than 15,000 feet deep at the bases of the islands. As Mauna Loa, the largest of the shield volcanoes (and also the world’s largest active volcano), projects 13,677 feet above sea level, its top is over 28,000 feet above the deep ocean floor.
- Cinder Volcanoes:
Cinder cones are the simplest type of volcano.
They are built from particles and blobs of congealed lava ejected from a single vent.
As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.
Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous throughout the volcanic terrains of the world.
Parícutin Volcano, Mexico, is a cinder cone rising approximately 1,200 feet above the surrounding plain.
- Composite volcanoes:
Some of the Earth’s grandest mountains are composite volcanoes–sometimes called stratovolcanoes.
They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases.
Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington.
Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone.
The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth’s crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.
- Caldera:
Magma is stored beneath a volcano in a magma chamber. When a very large, explosive eruption occurs that empties the magma chamber, the roof of the magma chamber can collapse to form a depression or bowl with very steep walls on the surface. These are calderas and can be tens of miles across.
Calderas can also be formed during an eruption that removes the summit of a single stratovolcano. Caldera-forming eruptions can remove massive portions of a single stratovolcano. The top can literally be blown off.
Example: Mount Tambora Volcano, Sumbawa Island, Indonesia
