GEOL105 Module 6: Volcanoes

Magma

Molten rock located beneath Earth's surface.

Lava

Molten rock that has reached Earth's surface.

Pyroclasts

Fragmented volcanic material blasted into the air during eruptions.

Magma Chamber

A pool of molten rock stored beneath a volcano.

Volcano Vent

An opening through which magma and gases erupt onto the surface.

Partial Melting

The incomplete melting of rocks, producing a silica-rich melt and a solid residue.

Solidus

The temperature curve below which a rock is completely solid.

Liquidus

The temperature curve above which a rock is completely melted.

Decompression Melting

Melting caused by a decrease in pressure as hot mantle rock rises.

Heat-Transfer Melting

Melting caused by heat injected from rising magma into cooler surrounding crust.

Flux Melting

Melting caused by the addition of water and volatiles that lower a rock's melting point.

Basaltic Mantle Melts

Hot, low-silica, iron- and magnesium-rich melts derived directly from the mantle.

Silica-Rich Continental Melts

Viscous, felsic melts produced by the melting of continental crust.

Volcanic Arcs

Chains of volcanoes formed above subduction zones, typically parallel to trenches.

Ring of Fire

A major belt of volcanoes and earthquakes ringing the Pacific Ocean basin.

Mafic Composition

Igneous composition low in silica and rich in iron and magnesium.

Intermediate Composition

Igneous composition with moderate silica content, between mafic and felsic.

Felsic Composition

Igneous composition high in silica and rich in feldspar and quartz.

Intrusive Cooling

Slow cooling of magma beneath the surface, allowing large crystals to form.

Extrusive Cooling

Rapid cooling of lava at the surface, resulting in small crystals.

Basalt and Gabbro

An extrusive and intrusive igneous rock pair with a mafic composition.

Andesite and Diorite

An extrusive and intrusive igneous rock pair with an intermediate composition.

Rhyolite and Granite

An extrusive and intrusive igneous rock pair with a felsic composition.

The Three Vs

Viscosity, volatiles, and volume, the primary factors controlling volcanic eruption styles.

Magma Viscosity Controls

Factors increasing viscosity, including lower temperature, higher silica, and more crystals.

Effusive Eruptions

Gentle, non-explosive outpourings of low-viscosity lava.

Explosive Eruptions

Violent blasts of gas-rich, highly viscous magma into pyroclasts.

Volcanic Explosivity Index (VEI)

A numerical scale measuring the relative size and explosiveness of volcanic eruptions.

Shield Volcanoes

Broad, gently sloping volcanoes built by successive flows of low-viscosity basaltic lava.

Flood Basalts

Vast plateaus formed by massive outpourings of highly fluid basaltic lava.

Scoria Cones

Small, steep-sided cones built from accumulations of erupted pyroclastic fragments.

Stratovolcanoes

Tall, cone-shaped composite volcanoes built from alternating layers of lava and pyroclasts.

Lava Domes

Steep-sided mounds formed by the extrusion of highly viscous, silica-rich lava.

Continental Calderas

Large volcanic depressions formed by catastrophic supervolcano collapse and massive eruptions.

Volcanic Ash

Fine-grained, jagged glass and rock fragments blasted into the atmosphere during eruptions.

Pyroclastic Flows

Fast-moving, superheated avalanches of gas, ash, and rock racing down volcano slopes.

Lahars

Destructive mudflows and debris flows composed of volcanic ash and water, often triggered without an eruption.

Volcanic Gases and Vog

Gases released during eruptions, including sulfur dioxide which creates volcanic smog or vog.

Volcano Monitoring

Methods used to track volcanic activity, including earthquakes, ground deformation, and gas emissions.

Volcano Hazard Mitigation

Measures to protect communities, including evacuation plans, acoustic flow monitors, and lahar levees.