What about volcanoes?
are products of melting mantles, a journey through the Earth’s crust,
and the discharge of pent-up gases. Deep inside the Earth, there is a layer
called the mantle. The
mantle is a solid body of rock in between the molten core and thin crust
at the surface. The beginning of the volcanic eruption begins with these
rocks. In this layer, there can be an extremely high temperature and lots
of pressure, as a result of this combination, the rock begins to melt and
transforms into a liquid rock, also called magma.
Since the layers of the Earth gets thinner and thinner, the immense mass
of magma formed will travel up towards the Earth’s denser layers and
will eventually reach the Earth’s surface and become lava.
There are many different lava types. Magma comes in different compositions so each of these different magma types will construct different lava types. There are fluid, fast-moving basalt to slower moving basalt, or more viscous andesite. The magma results are determined by the different collections of minerals in the rocks because all the minerals melt at different temperatures.
Volcanoes also erupt in different ways. The main reason for this has to do with plates.
Most volcanoes occur on plate boundaries. Plate boundaries are areas where Earth's shifting plates meet or split apart, usually with violent results.
Plate margins that are coming together are called convergent margins, while those that are splitting apart are called divergent. A third type, transform-fault margins, slide against each other and go in opposite directions (like those of the San Andreas Fault in California). Volcanoes can occur on convergent or divergent plate margins or over a hotspot, a spot inside the mantle that heats areas of the plate above it.
Along convergent margins, two plates meet and one descends beneath the other, a process called subduction. As the descending plate is forced deeper into the mantle, parts of it begin to melt and form magma that rises to the surface, often in explosive eruptions. Convergent margins tend to create large, classic, cone-shaped volcanoes called stratovolcanoes, such as Mt. St. Helens in Washington State.
At divergent margins, plates are coming apart and hot rock forces its way to the surface. Many divergent plate margins are under the oceans, creating long undersea rift zones that fill with lava. In some eruptions at divergent margins, the relatively calm, smooth flow of lava creates volcanoes with gently sloping sides, called shield volcanoes.
Hotspots can also cause shield volcanoes to form. As plates move over hotspots, volcanoes spring up and die down in turn, often creating an island chain. The Hawaiian Islands are the result of a hotspot.