A volcano is a crack in the crust of a planet like the earth. Magma can rise through the crack and erupt as lava on the surface of the planet. The ejected lava accumulates around the crack and a volcanic edifice grows. The shape of the volcano edifice depends on the amount of lava erupted and the lava type produced. Sometimes only a small cinder cone is created, or a hornito, another time a big mountain. When the lava is low viscous, it creates a shield volcano. When highly viscous lava eruptes, a steep stratovolcano forms.
Apart from lava, gases and volcanic ash can also be erupted. Before the volcano erupts, the magma accumulates in a magma chamber that lies beneath the volcano.
The magma is generated in the Earth’s mantle, by partial melting of mantle rocks, or subducted earth crust.
Most volcanoes are grown along the tectonic plate boundaries. 70% of the volcanoes are located in the Pacific Ring of Fire. This is marked by the plate boundaries to the Pacific plate. Most volcanoes along the Pacific Coast are dangerous subduction volcanoes. These volcanoes usually erupt explosively or produce lava dome. When lava domes collapse, pyroclastic flows are created. These stream down the volcanic slope and destroy everything on their way.
Some of the most spectacular volcanoes were created by Mantelplumes. These volcanoes are called hot spot volcanoes. One of the most famous hot spot volcanoes is the Kilauea in Hawaii. Its last big eruption took place in 2018. Most hot spot volcanoes erupt effusively. That is, they produce low-viscosity lava. This can form lava lakes, or lava fountains and lava flows. In these eruptions rarely people die, because you can usually get away from lava flows in safety. But there are also hot spot volcanoes like the Yellowstone caldera that produce a highly viscous lava. These volcanoes can cause gigantic explosive eruptions called super volcano eruptions. These have a VEI 8 and could trigger a global winter and thus the downfall of human civilization.
Up to 50 volcanoes erupt worldwide every year. Some of them are permanently active. These volcanoes include Stromboli in Italy and Dukono in Indonesia.