A volcano is an opening in a planet’s crust through which hot lava, tephra and gases come out from a magma reservoir. Magma refers to the molten or semi-molten rocks inside the Earth’s surface. There are 3 types of volcanoes classified on the basis of activity.
Active volcanoes are those which erupt frequently.
Dormant volcanoes are those which show signs of future eruption.
Extinct volcanoes are those which show no signs of eruption.
Types of Volcanoes classified on the basis of extrusive landforms
Stratovolcanoes (composite volcanoes)
These are the most common volcanoes. Stratovolcanoes have an almost conical shape e.g., Mount Fuji, Mount Vesuvius. These cones are built up by several eruption of volcanic materials from the main conduit. Each eruption adds a new layer to the sides of the volcano.
The lava that comes out of these volcanoes is acidic having a very high viscosity and a high silica content.
The lava doesn’t spread out far because of the high viscosity and a conical landform is formed around the conduit. These volcanoes may have various dykes feeding other vents on the sides of the volcano.
Stratovolcano eruptions are often explosive. A large amount of gas and pyroclastic material is thrown up in the atmosphere.
The less viscous lava forms the shield volcanoes. The less viscous basic lava flows easily and forms a shield like landform. The eruptions are generally non explosive (effusive eruption). The basic lava that flows out of the shield volcanoes has a low silica percentage.
Which is the highest active volcano in the world (above sea-level)?
These are simple volcanoes having a single vent. Cinder cone hills have steep slopes and there is a bowl shaped crater at the top . Pyroclastic materials such as volcanic ash and cinder is thrown up in the air during the eruption of lava fountain. The pyroclastic material cools and settles down to form loose conical hills. The highly viscous molten lava flows beneath the cinder cones. These volcanoes roughly reach a height of 1000 ft.
These are formed by the very viscous lava. Due to its high viscosity, the lava does not flow easily and starts piling up to form lava domes.
Caldera is a hollow formed when the magma reservoir is emptied and the ground above it collapses.
Answer to quick question
Ojos del Salado in the Andes is the highest active volcano in the world. It has an elevation of 6,893 m above sea-level. It is a stratovolcano.