Volcanism is the phenomenon of eruption of molten rock onto the surface of the Earth or a solid surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the
surface called a vent.
It includes all phenomena resulting from and causing magma within the crust or mantle of the
body, to rise through the crust and form volcanic rocks on the surface.
On Earth, volcanism occurs in several distinct geologic settings. Most of these are associated
with the boundaries of the enormous rigid plates that make up the lithosphere—the crust and
Magma from the mantle or lower crust rises through its crust towards the surface. If magma
reaches the surface, its behavior depends on the viscosity of the molten constituent rock.
Viscous (thick) magma produces volcanoes characterised by explosive eruptions, while nonviscous (runny) magma produce volcanoes characterised by effusive eruptions pouring large
amounts of lava onto the surface.
Aspects of volcanism
Volcanoes are places where magma reaches the earth’s surface. The type of volcano depends on
the location of the eruption and the consistency of the magma.
These are formed where magma pushes between existing rock, intrusions can be in the form
of batholiths, dikes, sills and layered intrusions.
Earthquakes are generally associated with plate tectonic activity, but some earthquakes are
generated as a result of volcanic activity.
The amount of gas and ash emitted by volcanic eruptions has a significant effect on the
Earth’s climate. Large eruptions correlate well with some significant climate change events.