Volcanic eruption

A volcano is a vent or fissure in Earth's crust through which lava, ash, rock and gases erupt. A volcano is also a mountain formed by the accumulation of these eruptive products. Let's take a look at how volcanoes form:

Earth's crust is 40 to 250 miles (64 to 402 kilometers) thick.It is broken up into 14 major and 38 smaller pieces called tectonic plates. These plates float on a layer of magma — semi-liquid rock and dissolved gases. At the boundaries of these plates — where they move past, are pushed under, or move away from each other — magma, which is lighter than the surrounding solid rock, is often able to force its way up through cracks and fissures. Magma can explode from the vent, or it can flow out of the volcano like an overflowing cup. Magma that has erupted is called lava. 

Principal types of volcanoes

Cinder cone volcanoes

Cinder cone volcanoes are the most common type of volcanoCinder cone volcanoes are fairly small, generally only about 300 feet (91 meters) tall and not rising more than 1,200 feet (366 meters). They can build up over short periods of a few months or years.

Stratovolcanoes

Stratovolcanoes are also called composite volcanoes because they are built of layers of alternating lava flow, ash and blocks of unmelted stone. They are larger than cinder cones, rising up to 8,000 feet.Stratovolcanoes erupt with great violence. Pressure builds in the magma chamber as gases, under immense heat and pressure, are dissolved in the liquid rock. When the magma reaches the conduits the pressure is released and the gases explode, like soda spewing out of a soda can that you shook up and opened suddenly.Stratovolcanoes are considered the most violent eruptions.

 Shield volcanoes

 Shield volcanoes are huge, gently sloping volcanoes built of very thin lava spreading out in all directions from a central vent. The world’s largest volcano, Mauna Loa in Hawaii, is a shield volcano. Mauna Loa is about 55,770 feet.

Lava domes 

Lava domesare built up when the lava is too viscous to flow. A bubble or plug of cooling rock forms over a fissure. This cooler, thick lava usually rises near the end of an explosive eruption and lava domes often form within the craters of stratovolcanoes.