Volcanism are the events involved in the formation of volcanoes, namely the movement of magma in the earth's crust to infiltrate the upper layers of the earth's surface or exit. Symptoms of volcanism include:
a. Magma intrusion, the breakthrough process of magma into the crust of the earth but did not get off the ground. Formation due to intrusion of magma are:
1) Batholit, is a frozen magma chamber
2) Lakolith, is formed where the upper convex and flat bottom
3) Sill, was formed by the intrusion of magma between two layers of sediment where the top and bottom flat
4) Gang, was formed by the intrusion of magma through a narrow gap
5) Apofisa, is a branch of the gang
6) Diatrema or excavation, is formed by magma intrusion that happened on pit crater (diatrema).
b. Magma extrusion (eruption), the process of magma to break out of the earth's surface. Extrusion is also called the eruption magma (volcanic eruptions).
Based on the nature of the eruption eruptions are divided into:
1) effusive eruption, the volcano eruption that does not cause an explosion, the material is usually liquid (molten)
2) explosive eruption, the volcanic eruption that causes an explosion. Eruptions are usually solid and liquid material ejects.
Based on the exit hole forms magma, eruption is divided into:
1) linear eruption, the magma discharge where the line shape (elongated)
2) eruption area, where the discharge of a large hole shaped magma nearby magma chamber due to the earth's surface
3) The central eruption, the magma-shaped exit holes where relatively small.
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