Types of volcanoes

A volcano is a land-form, a mountain, where molten rocks erupt through the surface of the planet. The volcano mountain opens downwards to a pool of molten rocks below the surface of the earth.

When the pressure builds up in the earth’s crust, eruptions occurs. Gasses and rock shoots up through the opening and spill over or fill the air with lava fragments. The volcano eruption can cause lateral blasts, hot ash and lava flow, mud-slides and more.

Types of volcanoes

Categories of Volcanoes

Volcanoes are categorized into three main categories:

  • Active
  • Dormant
  • Extinct

An active volcano is one which is recently erupted and there is a possibility that it may erupt soon.

A dormant volcano is one which has not erupted in a long time but there is a possibility it can erupt in the future.

An extinct volcano is one which has erupted thousands of years ago and there’s no possibility of eruption.

Types of Volcanoes

Volcanoes are grouped into four types:

  • Cinder cones
  • Composite volcanoes
  • Shield volcanoes
  • Lava volcanoes
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.

Cinder cones

Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own.

Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris. These types of volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that gives rise to the name.

Composite volcanoes

Composite volcanoes are made of cinders, ash, and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process repeats.

Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows. These are formed by the eruption of low-viscosity lava that can flow a great distance from a vent.

Shield volcanoes

They generally do not explode catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

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.

Lava domes

They are sometimes formed within the crater of a previous volcanic eruption. Like composite volcano, they can produce violent, explosive eruptions, but their lava generally does not flow far from the originating vent.

Practise This Question

An LCR series circuit with a resistance of 100 ohm is connected to an ac source of 100 V (r.m.s.) and angular frequency 300 rad/s. When only the capacitor is removed, the current lags behind the voltage by . When only the inductor is removed the current leads the voltage by . The average power dissipated is