The Earth's core is solid iron, and pressure in this region is very high. The mantle is made of solid rock and minerals. Due to the heat emitting from the mantle, the rocks are soft and ductile, but Earth's mantle cannot be considered molten. It a solid that moves or deforms under pressure. Small movement, therefore, occurs in the earth's mantle.
On top of the Earth's mantle is the crust. The crust is comprised of tectonic plates that rest on the upper mantle. Because of the ductile nature of the mantle, tectonic plates move very slowly, but move nonetheless.
Subduction Zones:-
Volcanoes are formed when the edges of tectonic plates meet. These regions are called convergent boundaries. When they collide, they are called subduction zones. When they move apart, they are called divergent boundaries.
Volcanoes emerge in subduction zones, where two tectonic plates collide.
One tectonic plate moves under another plate, pushing it down into the upper mantle. This causes a change in the temperature and pressure above the submerged plate. Magma then forms as a result of lower pressure and increased temperature.
The Formation of Magma:-
Magma forms within the earth's upper mantle when two tectonic plates collide to create a subduction zone. Lower pressure above the submerged plate and below the top plate causes the rocks in the mantle to begin melting.
Magma is less dense than rocks, which means that it is also lighter. It follows the same rules as air: hot air rises, and cold air falls. Because magma is hot, it rises through the Earth's crust, and because rocks are cold and dense, they fall through the Earth's crust.
Before volcanoes erupt, the magma sloshes around in the upper mantle. Magma may cool and form igneous rocks and crystals below the surface, but it may also move into magma chambers, which are large pools of magma below the Earth's crust. When a volcano erupts, what emerges is magma that continued to move up through the Earth's crust until it finally escaped.
Volcanic Eruption:-
When the pressure within the magma chamber is greater than the strength of the crust, it begins to break through.
Magma rises to the Earth’s surface for a combination of reasons. Inside the magma chamber there are a number of gases that are mixed with the magma. Just like a carbonated drink, the bubbles of gas rise to the surface of the magma chamber, pushing against the Earth's crust.
Another reason an eruption can occur is simply an overload of magma in the magma chamber. Once the chamber is filled to capacity, an eruption is sure to occur.
Determining the Force of Eruptions:-
Inside the magma chamber there is a volatile mix of reactions taking place. No two samples of magma are identical, so the magma erupting from one volcano will be slightly different than another.
Thick, sticky magma results in stronger eruptions, whereas thinner magma causes less extreme eruptions. The thickness of magma is determined by the temperature of and how much water, silica, and gas it contains.
Silica is a crystalline rock material that causes magma to thicken. Hotter magma is also thicker. Thick magma makes it harder for the bubbles of gas to escape, so there is more pressure when the volcano finally erupts. The higher the amount of gases within the magma, the more force an eruption will have. Thin magma allows gas bubbles to escape easily, so the eruption is less violent.
