WHAT IS VOLCANISM?

Volcanism is phenomenon of eruption of molten rock on the surface of earth or a solid surface planet , Where lava and volcanic gases erupt through a break called vent.

REASONS FOR VOLCANISM

Boundaries of enormous rigid plates that make up the crust and upper mantle.
Oceanic ridge system , where plates move apart on both sides of the ridge and magma wells up from the mantle, creating a new ocean floor along the trailing edges of both plates. Virtually all of this volcanic activity occurs under water. In few places , the oceanic ridges are sufficiently elevated above the deep seafloor that they emerge from the ocean, and subaerial volcanism occurs.

Volcanism can be defined as an igneous activity which includes the following.

Formation of magma.
Upward movement of magma.
Ejection on the surface.
Cooling and Solidification.

INTRUSIVE VOLCANISM

Intrusive volcanism is when magma is forced into the rocks that make up earth's crust. When it cools and becomes solid while still underground , different features called plutons are formed. The rock formed is an intrusive igneous rock.

The cooling and solidification of magma can happen both inside and over the surface of earth. In the process the following types of magma based landforms are created inside of earth.

Batholiths : A formation of large scale magma that has been solidified at the base of a mountain.
Laccoliths: A small scale magma that pushes the overlying layers of rocks to form a dome- shaped structure.
Lapoliths : It is a small scale magma cooled near the earth's surface that lies horizontally to the existing rocks.
Phacoliths : It is a pluton of igneous rock parallel to the bedding plane or foliation of folded country rock.
Sills/sheets : small scale magma cooled near the earth's surface that lies horizontally to the existing rocks.
Dikes : Small scale magma cooled within the earth's crust that stands vertically to the existing rocks.

EXTRUSIVE VOLCANISM

The molten magma under great pressure forces its way through the fissure of underground rocks and reaches the earth's surface. The formation as a result of this volcanic movement forms igneous extrusion.

Caldera : Large cauldron like hollow that forms shortly after the emptying of a magma chamber/ reservoir in a volcanic eruption. When it is filled with water it is called a "Caldera lake".
Composite cones: Large volcanic mountains formed by solidified lava on the surface.
Geysers : It is a vent in earth's surface that periodically ejects a column of hot water and steam.
Hot spring : Also called geothermal spring is a spring produced by the emergence of geothermally heated ground water that rises from earth's crust.