Lesson 4 – Volcanism

Vocabulary flashcards covering definitions, eruption styles, volcano types, hazards, and notable examples from the Lesson 4 Volcanism lecture.

Volcano

An opening in Earth’s surface through which lava, ash, and gases escape.

Volcanism

All phenomena related to the eruption of molten lava onto a planet’s surface.

Magma Chamber

Sub-surface reservoir where molten rock accumulates before rising to the vent.

Vent

Central opening of a volcano through which magma reaches the surface.

Fumarole

A small vent that emits volcanic gases and vapors.

Lava Dome (feature)

Mound-shaped protrusion formed by the slow extrusion of very viscous lava.

Pyroclastic Flow

Dense, fast-moving cloud of hot gas, ash, and volcanic debris that races downslope.

Lahar

Volcanic mudflow composed of water, ash, and rock fragments; often more deadly than lava.

Shield Volcano

Broad volcano with gentle slopes built by low-viscosity, basaltic lava flows (e.g., Mauna Loa).

Stratovolcano (Composite)

Steep, cone-shaped volcano built of alternating layers of viscous lava and pyroclastics; prone to explosive eruptions (e.g., Mt. Vesuvius).

Cinder Cone

Small, common volcano made of loose pyroclastic fragments (scoria); also called a scoria cone.

Caldera

Large volcanic depression formed when a volcano collapses after a major eruption (e.g., Yellowstone).

Lava Dome Volcano

Steep-sided volcano created by thick, highly viscous lava piling up near the vent.

Basaltic Lava

Low-viscosity, runny lava rich in iron and magnesium; typical of shield volcanoes.

Viscosity (lava)

Resistance of magma or lava to flow; higher viscosity leads to more explosive eruptions.

Phreatic Eruption

Steam-driven explosion involving heated groundwater, water, steam, and ash—no new magma.

Vulcanian Eruption

Short, violent eruption caused by pressurized magma gases; produces ash-laden cauliflower clouds.

Strombolian Eruption

Moderately explosive bursts of basaltic lava fountains and glowing cinder bombs.

Pelean Eruption

Eruption of viscous, gas-rich lava forming a dome and destructive glowing avalanches (nuée ardente).

Phreatomagmatic Eruption

Explosion caused by interaction of ascending magma with groundwater, forming high eruption columns and ring-shaped base clouds.

Plinian Eruption

Extremely explosive eruption producing towering, umbrella-shaped ash columns that reach the stratosphere.

Icelandic Eruption

Effusive outpouring of basaltic lava from long fissures, building lava plateaus.

Hawaiian Eruption

Non-explosive eruption of fluid basalt forming fire fountains and lava rivers.

Active Volcano

A volcano that has erupted within historic time and shows signs of activity.

Dormant (Potentially Active)

A volcano that has not erupted in the last 10,000 years but could erupt again.

Extinct Volcano

A volcano not expected to erupt again; no activity in recorded or geological history.

Convergent Zone Volcanism

Volcanoes generated above subduction zones where one plate sinks beneath another.

Island Arc

Chain of volcanic islands formed above an oceanic-oceanic subduction zone.

Volcanic Arc

Series of volcanoes on the continental side of an oceanic-continental subduction zone.

Hotspot

Stationary mantle plume that generates magma within a tectonic plate, forming chains like Hawaii.

Seafloor Spreading Volcanism

Magma upwelling along mid-ocean ridges, building new oceanic crust.

Pyroclastic Materials

Fragments ejected during eruptions: ash, lapilli, blocks, and bombs.

Pahoehoe Lava

Smooth, ropy-surfaced basaltic lava with low viscosity.

A‘a Lava

Rough, jagged basaltic lava with sharp edges; hazardous to cross.

Lava Pillow

Pillow-shaped masses of basalt formed by underwater lava extrusion.

Volcanic Ash

Fine (<2 mm) fragments of rock, mineral, and glass expelled during eruptions; hazardous to health and infrastructure.

Water Vapor (Volcanic Gas)

Most abundant volcanic gas; generally harmless but indicates magma degassing.

Sulfur Dioxide Aerosols

SO₂ combining with water in the stratosphere to form droplets that reflect sunlight and cool Earth.

Geothermal Energy

Renewable heat energy harnessed from subsurface magma or hot groundwater near volcanoes.

Nuée Ardente

French for “glowing cloud”; a hot, dense pyroclastic avalanche typical of Pelean eruptions.

Jökulhlaup

Glacial outburst flood often triggered by subglacial volcanic activity.

Eruption Column (Plume)

Vertical cloud of ash, gas, and tephra rising above an explosive eruption.

Mantle Degassing

Release of water and volatiles from magma as it ascends and crystallizes, adding water to Earth’s surface.

Mayon Volcano

Philippines’ most active stratovolcano, famous for its near-perfect cone shape.

Mount Kanlaon

The Philippines’ third most active volcano; erupted moderately on 08 April 2025.

Ring of Fire

Circum-Pacific belt with intense subduction-related volcanism and earthquakes.

Yellowstone Caldera

Massive caldera in the United States formed by past super-eruptions; hotspot-related.

Toba Caldera

Large caldera in Indonesia associated with one of Earth’s largest Quaternary eruptions.

Mauna Loa

One of the world’s largest shield volcanoes, located in Hawaii.

Mount Vesuvius

Italian stratovolcano famed for its AD 79 Plinian eruption that buried Pompeii.