Volcano erupt due to the extreme temperature inside Earth. This extreme heat melt the Rock inside the earth and from a thick liquid substance. The molten rock is not as dense as the surrounding rocks and does rises upward and collect in Chambers. Some of these molten rock is pushed outside from the cracks or fissures on the surface of earth. This make a Volcano erupt and the thick molten Rock comes out. The thick flowing substance that forms from the melting of Rock deep in the earth crust is called Magma. Lava is the Magma that comes out during the volcanic eruption. A dormant volcano is a volcano that has not erupted recently but may erupt in future. Mauna loa is an active volcano and the largest volcano on the earth the Summit of the volcano is about 17 kilometres above its base.