Volcanoes are geological features that result from the release of molten rock, ash, and gases from the Earth's interior. They form when magma rises to the surface through a vent or fissure, and the resulting eruption can create a range of landscapes, from broad shield volcanoes with gentle slopes to steep-sided stratovolcanoes with explosive eruptions. Volcanoes can be found at divergent plate boundaries, where new oceanic crust is formed, and at convergent plate boundaries, where two plates collide and one is forced beneath the other into the mantle.
Volcanoes are often classified based on the type of material that is erupted. Shield volcanoes are made up of many thin flows of fluid basaltic lava, while stratovolcanoes are composed of more viscous andesitic lava and pyroclastic material. Calderas, which are large, circular depressions formed by the collapse of a volcano, can also be found at some volcanoes.
In addition to eruptions, volcanoes can also affect the surrounding environment through processes such as gas emissions, lava flows, and pyroclastic flows, which are fast-moving avalanches of hot ash, rock fragments, and gas. Volcanoes can also trigger earthquakes and tsunamis, and their ash can have a significant impact on the atmosphere and climate.
Despite the hazards associated with volcanic activity, many people live near or on volcanoes because of the fertile soil and geothermal resources that they provide. Volcanoes are also an important part of the Earth's history, and their study has helped scientists to better understand the processes that occur within the Earth.