E&E 151 S Introductory Geology: Chapter 4 (Volcanoes) Definitive Study

Volcanism

The process that occurs when magma makes its way to the Earth's surface.

Explosive (Pyroclastic) Eruption

An eruption dominated by the generation of solid volcanic fragments, driven by the expansion of gases in viscous magma.

Effusive Eruption

An eruption characterized by lava extruding out of vents and fissures in the ground, typically less dangerous than explosive eruptions.

Viscosity

A fluid's resistance to flow, determined in magma by silica content, temperature, and dissolved gas.

Mafic Magma (Basalt)

Silica-deficient magma (around 50% SiO2) that flows easily and typically produces effusive eruptions.

Felsic Magma (Rhyolite)

Silica-rich magma (65% or more SiO2) that is highly viscous and leads to large, explosive eruptions.

Intermediate Magma (Andesite)

Magma with silica content between felsic and mafic, capable of producing either violent explosions or lava flows depending on gas content.

Pyroclasts (Tephra)

Fragments of magma blasted into the air during an explosive eruption, ranging in size from fine dust to massive blocks.

Volcanic Explosivity Index (VEI)

A logarithmic scale from 0 to 8 used to measure eruption power based on erupted volume, plume height, and duration.

Active Volcano

A volcano that is currently erupting or has erupted recently.

Dormant Volcano

A volcano that has not erupted in thousands of years but is expected to erupt again in the future.

Extinct Volcano

A volcano that has not erupted for a very long time and shows no signs of ever erupting again.

Mitigation

The process of reducing volcanic eruption impacts through hazard mapping, monitoring (seismic, gas, deformation), and public alerts.

Decompression Melting

Melting of the asthenosphere driven by a drop in pressure at divergent boundaries or hot spots, generating low-water basaltic magma.

Flux Melting

Melting caused when subducting oceanic crust releases water into the asthenosphere, lowering its melting temperature and generating viscous, water-rich magma at convergent boundaries.