vulkanism

Vulkanism is the geological process by which magma and volcanic gases escape from the interior of a planet to the surface or near-surface. It includes the generation of magma, its ascent through the crust, and eruption of lava, ash, pumice, and gases, as well as related ground deformation and hydrothermal activity.

Magma forms by partial melting of existing rocks in the mantle or crust, and rises because it is less dense than surrounding solid rock. Here it may accumulate in magma chambers and, under pressure, fracture surrounding rock to feed conduits that reach the surface. Eruptions vary in style and product, producing lava flows, ash plumes, volcanic bombs, and pumice. Effusive eruptions emit low-viscosity lava that can form shield volcanoes and lava fields; explosive eruptions eject ash clouds, pumice, and gas, and can create stratovolcanoes and calderas.

Most Earth volcanism is linked to plate tectonics: at divergent boundaries, mid-ocean ridges and continental rifts; at convergent boundaries with subduction, and at volcanic hotspots such as ocean island chains. Some volcanoes erupt repeatedly for short periods (strombolian, vulcanian, plinian styles) while others erupt intermittently over long timescales. Ground deformation, seismicity, gas emissions, and satellite observations are used to monitor activity and forecast eruptions.

Hazards include ash fall, pyroclastic flows, lava flows, lahars, volcanic gas emissions, and climate impacts. Volcanism also occurs beyond Earth, with evidence of volcanic activity on planets and moons such as Mars, Venus, Io, and periodic eruptions observed elsewhere.