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 occur. 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.
Categories of Volcanoes
Volcanoes are categorized into three main categories:
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 an eruption.
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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.
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 give rise to the name.
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.
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.
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.
Types of Volcanic Eruptions
Types of volcanic eruptions depends on various factors such as chemistry of magma, temperature, viscosity, volume, presence of groundwater, and water and gas content.
Following are the different types of volcanic eruptions:
- Hydrothermal eruption: These eruptions include ash and not magma. They are driven by the heat caused in hydrothermal systems.
- Phreatic eruption: This is driven when the heat of the magma interacts with the water. These eruptions too do not include magma and only ash.
- Phreatomagmatic eruption: This eruption takes place when there is interaction between the newly formed magma and water.
- Strombolian and Hawaiian eruption: Hawaiian eruption has fire fountains while Strombolian eruption has explosions due to lava fragments.
- Vulcanian eruption: These eruptions lasts for short period of time and can reach up to a height of 20 km.
- Subplinian and Phinian eruptions: Subplinian eruptions reach up to 20 km height, while Plinian eruptions reach up to 20-35 km.