Volcanoes and Volcanic Hazards Part 2

Volcano

A vent, hill, or mountain from which molten or hot rocks with gaseous materials have been ejected.

Volcanism

A rock-forming process, a geologic hazard, and a potential energy resource.

Magma

Molten rock located beneath the Earth's surface.

Lava

Magma that has been extruded onto the Earth's surface.

Magma Chamber

A large underground pocket where magma collects before an eruption.

Vent

Any opening at the Earth's surface through which magma or volcanic gases are emitted.

Crater

A bowl-shaped area that forms around a volcano's central vent.

Conduit

A pipe or channel that carries magma from the chamber to the surface.

Stratovolcano (Composite)

A steep-sided, cone-shaped volcano built by eruptions of viscous lava and pyroclastic material, typically found at convergent boundaries.

Shield Volcano

A broad, gently sloping volcano built by effusive eruptions of low-viscosity basaltic lava.

Magmatic Eruption

An eruption driven by the decompression of dissolved gases within magma.

Phreatic Eruption

A steam-driven explosion caused by groundwater flashing to steam upon contact with magma, with no magmatic release.

Phreatomagmatic Eruption

An explosion resulting from the direct interaction of water and magma, releasing both magma and vapor.

Viscosity

The resistance of a fluid to flow; in magma, it is primarily controlled by silica content and temperature.

Mafic Magma

Magma with low silica content (45-55%), low viscosity, high temperature, and low explosivity; typically forms basalt.

Felsic Magma

Magma with high silica content (>63%), high viscosity, lower temperature, and high explosivity; typically forms rhyolite.

Divergent Boundary Volcanism

Characterized by effusive eruptions of mafic lava, forming shield volcanoes and new oceanic crust.

Convergent Boundary Volcanism

Characterized by explosive eruptions of intermediate to felsic lava, forming stratovolcanoes and island/continental arcs.

Flux Melting

Melting triggered at convergent boundaries when water from a subducting plate lowers the melting point of the overlying mantle.

Decompression Melting

Melting that occurs when mantle rock rises and pressure decreases, typically at divergent boundaries.

Magmatic Differentiation

The process by which magma changes composition, becoming more felsic through assimilation and fractional crystallization.

Assimilation

The process where magma incorporates and melts surrounding country rock, increasing its silica content.

Fractional Crystallization

The process where early-forming minerals crystallize and settle out, leaving the remaining melt more silica-rich.

Tephra

A general term for all fragmental material ejected during a volcanic eruption.

Pyroclastic Flow

A fast-moving, ground-hugging current of hot gas, ash, and rock fragments.

Lahar

A destructive volcanic mudflow or debris flow composed of water and volcanic sediment.

Lava Dome

A steep-sided mound formed by the extrusion of viscous lava from a vent.

Eruption Column

A vertical pillar of superheated ash, tephra, and gases rising above a vent during an explosive eruption.

Volcanic Gases

Gases released from magma, primarily water vapor, carbon dioxide, and sulfur dioxide.

Lateral Blast

A sideways-directed volcanic explosion that can devastate a wide area.

Volcanic Tsunami

A tsunami generated by volcanic activity, such as a flank collapse or submarine eruption.

Debris Avalanche

A rapid, large-scale slope failure of a volcanic edifice.

PHIVOLCS

The Philippine Institute of Volcanology and Seismology, the national agency monitoring volcanic activity in the Philippines.

Active Volcano (PHIVOLCS)

A volcano that has erupted within the last 600 years (historical times) or within the last 10,000 years (Holocene).

PHIVOLCS Alert Level System

A 0-5 scale used to communicate the status of an active volcano and guide public safety measures.

Permanent Danger Zone (PDZ)

A designated high-risk area around a volcano where entry is restricted due to constant hazards