volcanism

Volcanism refers to the processes by which magma from the Earth’s interior, volcanic ash, and gases are produced, stored, moved, and expelled onto or near the surface. It includes intrusive activity that forms magma chambers and underground structures as well as effusive and explosive eruptions that deliver lava and tephra to the surface. Volcanism is driven by heat from the mantle and crust, changes in pressure as rocks melt and ascent continues, and the presence of volatiles such as water vapor and carbon dioxide that exsolve from melt.

Most volcanism occurs at plate boundaries and in intraplate settings. At divergent boundaries, rising mantle material partial melts as pressure drops. At convergent boundaries, subduction introduces water into the mantle, lowering melting temperatures. Hot spots generate volcanism away from plate edges as plumes of hot mantle material rise. Submarine volcanism is also widespread and shapes the ocean floor.

Forms and products of volcanism include both effusive eruptions that produce lava flows and build shield volcanoes, and explosive eruptions that eject ash clouds, pumice, and volcanic bombs, forming stratovolcanoes and calderas. Volcanic materials range from lava and ash to pumice, tephra, lahars, and a variety of volcanic gases such as water vapor, carbon dioxide, and sulfur dioxide.

Hazards associated with volcanism include ashfall, pyroclastic flows, lava flows, lahar floods, volcanic gases, landslides, and tsunami generation in coastal zones. Volcanism is studied through seismology, ground deformation measurements, gas monitoring, and thermal imaging, contributing to our understanding of planetary interiors and crustal development.