This is the process by which molten materials from the mantle (magma) are intruded into the Earth’s crust but also extruded from the crust.
This refers to the ways by which magma is intruded into the earth’s crust. Through fracture, fissures found in the crust magma found inside the crust can sometimes reach the surface of the crust and consolidate from there. In this case, the features formed are extrusive features. Some other times magma can fail to reach the earth’s surface and consolidate inside the crust before it reaches the surface. In this case, the features formed are known as intrusive features.
The causes of volcanicity and volcanic eruption can include:
- Increased quantity of magma in the mantle leading to an increase to the pressure pushing this magma outwards.
- Presence of fissure and cracks allowing magma to move towards the crust.
- Increase in the temperature of magma inside making the magma very light to move along a crack.
- An increase in the vent allowing a big quantity of magma to move in at once.
Types of volcanoes.
According to the mode of eruption
- Hawaiian volcanoes: Emission of fluid magma, no projection, no explosion. Such volcanoes don’t have volcanic cones most of the time. Magma solidifies very far from the crater.
- Strombolian volcanoes: magma is a bit viscous, little projections of pyroclasts can be seen and the volcanic cone is formed.
- Vulcanian volcanoes: magma is now viscous and consolidates not far from the crater. Projection of pyroclasts is now common and the cone can alternate layer of ash and consolidate magma.
- Pelean volcanoes: Magma is very viscous and consolidates even in the vent before reaching the earth’s crust. In this type is the projection, explosion of magma consolidated in the vent as bombs, projections of very black smokes.
According to the volcano activity.
- Active volcanoes: these are volcanoes which can enter into eruption at any period. In this area there are frequent earth quakes and signs of fire are observed at night on the crater of such volcanoes. Temperature is very high inside.
- Extinct volcanoes: Magma inside cools down and consolidates inside the volcano. There is nothing can be observed on the crater. Most the time the crater falls into the vent and depression are formed on the crater. This depression collects water later to form crater lakes.
- Dormant volcanoes. It is a volcano between two periods of eruption. The cycle of volcanoes eruption depends from one volcano to another.
According to the structure of volcanoes.
- Simple volcanoes. They are simply formed by a single crater, vent, and volcanic cone formed by just a single layer.
Composite volcano. They are complex, formed by several craters, vents, and cone let. The volcanic cone shows different layers of ash, lava.
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