Key Terms: Volcanic Hazards (AQA A Level Geography): Revision Note

Vulcanicity and tectonics - key terms

Effusive eruption – A gentle volcanic eruption where low-viscosity lava flows steadily rather than exploding violently.

Explosive eruption – A violent volcanic eruption caused by high-viscosity magma that traps gases, resulting in a powerful release.

Hot spot – A volcanic area not at a plate boundary, where a magma plume from the mantle creates volcanoes (e.g. Hawaii).

Ring of Fire – A major zone of volcanic and earthquake activity surrounding the Pacific Ocean, where about 75% of the world's volcanoes occur.

Volcanic Explosivity Index (VEI) – A scale from 0 to 8 that ranks the magnitude of volcanic eruptions based on the volume of material, eruption height, and duration.

Forms of volcanic hazard - key terms

Acid rain – Rainfall made acidic when sulphur dioxide from an eruption reacts with water vapour in the atmosphere.

Ash fallout – Fine volcanic ash carried by the wind, potentially causing health problems, disrupting transport, and damaging infrastructure.

Jökulhlaup – A sudden glacial flood caused by volcanic activity melting ice, often leading to significant damage.

Lahar – A destructive volcanic mudflow formed when volcanic material mixes with water (from rainfall or melting snow/ice).

Lava flow – Molten rock flowing from a volcano, which varies in speed but generally causes property and environmental damage.

Primary hazard – A direct result of a volcanic eruption, including tephra, ash, lava flows, pyroclastic flows, and volcanic gases.

Pyroclastic flow – A fast-moving, superheated mixture of gas and tephra that destroys nearly everything in its path.

Secondary hazard – Hazards resulting from primary effects, such as lahars, jökulhlaups, and acid rain.

Tephra – Solid material ejected during a volcanic eruption, ranging from fine ash to large volcanic bombs.

Volcanic gases – Emissions such as sulphur dioxide and carbon dioxide that can harm human health and contribute to acid rain.

Prediction of hazard events - key terms

Early warning system – A system used to alert people of impending volcanic activity, often based on real-time monitoring.

Ground deformation – The bulging or swelling of land around a volcano due to rising magma, used as a sign of imminent eruption.

Seismic activity – Earthquake activity often caused by magma movement, used as a key indicator in volcanic monitoring.

Shield volcano – A broad, gently sloping volcano formed by low-viscosity basaltic lava; erupts frequently with low explosivity.

Stratovolcano (composite volcano) – A steep-sided volcano built of alternating layers of ash and lava, typically found at destructive margins with less frequent but more explosive eruptions.

Volcanic prediction – The process of forecasting eruptions by monitoring geological signs using tools like GPS, tiltmeters, seismometers, gas sensors, satellites, and thermal imaging.

Volcanologist – A scientist who studies volcanoes and volcanic activity, particularly for the purpose of hazard prediction and mitigation.

Impacts and responses: Volcanic activity - key terms

Adaptation – Adjusting human activities to cope with volcanic risk, for example by promoting tourism as an alternative income source.

Long-term response – Efforts to reduce future impacts, including hazard mapping, land-use planning, building codes, education, and volcano monitoring systems.

Mitigation – Strategies designed to reduce or eliminate the impact of volcanic hazards, such as diverting lava flows or reinforcing structures.

Preparedness – Ensuring that communities are ready to respond to an eruption through training, drills, and communication systems.

Prevention – Limiting human activity in high-risk areas through land-use zoning or restrictions (though eruptions cannot be stopped).

Primary impact – The immediate effects of an eruption, including injury, death, and destruction of buildings, roads, and services.

Response (short-term) – Immediate actions such as evacuation, emergency aid, and search and rescue following an eruption.

Secondary impact – Long-term consequences such as economic loss, homelessness, mental health issues, and environmental degradation.