Eruption

An eruption is the rapid expulsion of material from beneath Earth's surface. In geology, it most commonly refers to volcanic eruptions, during which magma, ash, volcanic bombs, and gases are expelled through vents. Eruptions can be explosive, ejecting ash clouds and pumice, or effusive, producing lava flows.

Explosive eruptions involve rapid fragmentation of magma due to high gas pressure, forming tephra, ash clouds, pumice, and pyroclastic flows. Effusive eruptions emit lava that flows along the surface, often forming lava flows, lava domes, and shield volcanoes.

The onset is governed by magma viscosity, temperature, gas content, and pressure changes in the magma chamber. When magma rises and degasses, fracturing occurs, allowing magma to ascend to the surface. Seafloor eruptions and subglacial eruptions are common in different settings.

Hazards include ash fall that disrupts air travel and agriculture, pyroclastic flows, lava flows, landslides, tsunamis from volcanic explosions, and climatic effects from aerosol injection into the stratosphere.

Monitoring uses seismology, gas analysis, satellite imagery, and ground deformation measurements to forecast eruptions and issue alerts. Hazard maps and exclusion zones help protect nearby populations and infrastructure.

Notable examples include Mount Vesuvius, Krakatoa, and Mount St. Helens. Eruptions are studied by volcanologists to understand magma systems and to mitigate risks to nearby communities.