Tectonic Hazards: Key Terms (Cambridge (CIE) IGCSE Geography): Revision Note

Tectonic Hazards: Key Terms

Characteristics of the Earth's structure

Asthenosphere – A partially molten, plastic-like part of the upper mantle that allows tectonic plates to move on top of it.

Continental crust – The thicker (25–100 km), older, and less dense part of the Earth’s crust made mainly of granite.

Convection currents – Circular movements of heated material in the mantle that drive tectonic plate movement.

Core – The central part of the Earth, made up of a solid inner core and a semi-molten outer core, both very hot and made mostly of iron and nickel.

Crust – The Earth's outer layer, made of solid rock. There are two types: oceanic and continental.

Geothermal heat – Heat from within the Earth, mainly caused by radioactive decay, which drives convection currents.

Inner core – The solid centre of the Earth, about 1400 km wide, with temperatures between 5000–6000°C.

Lithosphere – The rigid outer layer of the Earth, made up of the crust and the solid upper part of the mantle.

Lower mantle – The solid part of the mantle beneath the asthenosphere; it is the thickest Earth layer at about 2900 km.

Mantle – The thick layer between the crust and the outer core, mostly semi-molten rock where convection currents occur.

Mantle plume – A column of very hot rock rising through the mantle, sometimes causing volcanoes away from plate boundaries (hotspots).

Oceanic crust – The thinner (5–10 km), denser and younger part of the crust made mostly of basalt; it is constantly being created and destroyed.

Outer core – A liquid metal layer about 2100 km thick beneath the mantle, where temperatures are 4000–6000°C.

Slab pull – A theory that tectonic plates are pulled along as a heavy, subducting oceanic plate sinks into the mantle.

Tectonic plate – Large sections of the Earth's lithosphere that move slowly over the mantle and cause earthquakes and volcanoes.

Processes and Features of Earthquakes & Volcanoes

Ash – Fine volcanic dust, less than 2 mm in size, ejected during eruptions and capable of travelling long distances.

Collision boundary – A type of plate boundary where two continental plates collide, pushing land upwards to form fold mountains.

Composite volcano (Strato-volcano) – A steep-sided volcano with sticky lava and explosive eruptions, usually found at destructive boundaries.

Constructive (divergent) boundary – A plate boundary where tectonic plates move apart, allowing magma to rise and form new crust and volcanoes.

Conservative (transform) boundary – A plate boundary where plates slide past each other, causing earthquakes but no volcanoes.

Destructive (convergent) boundary – A plate boundary where an oceanic plate sinks under a continental plate, causing volcanic eruptions and earthquakes.

Earthquake – A sudden shaking of the ground caused by the release of pressure along faults at plate boundaries.

Epicentre – The point on the Earth’s surface directly above the earthquake’s focus.

Focus – The point underground where an earthquake starts.

Hotspot – A place where magma rises through the mantle at a point away from plate boundaries, forming volcanoes.

Lahar – A dangerous volcanic mudflow formed when volcanic ash mixes with rainwater or melted snow.

Lava – Magma that erupts onto the Earth’s surface through a volcano.

Magnitude – The amount of energy released by an earthquake, measured on the Moment Magnitude Scale.

Mercalli Scale – A scale used to measure the damage caused by an earthquake.

Pyroclastic flow – A fast-moving, hot cloud of gas, ash and volcanic rock that flows down the side of a volcano during an eruption.

Ring of Fire – An area around the edges of the Pacific Ocean where many earthquakes and volcanoes occur.

Seismic waves – The vibrations that travel through the Earth from the earthquake focus, felt as shaking on the surface.

Shield volcano – A volcano with gentle slopes, runny lava, and frequent but mild eruptions, often found at constructive boundaries or hotspots.

Tephra – All material, including ash and rock, that is blasted into the air during a volcanic eruption.

Toxic gases – Harmful gases like carbon dioxide and sulphur dioxide released during a volcanic eruption.

Volcanic Explosivity Index (VEI) – A scale used to measure the strength and explosiveness of a volcanic eruption.

Impacts of Tectonic Hazards

Ash cloud – Fine particles of volcanic rock released into the air during eruptions, which can disrupt flights and affect air quality.

Cholera – A disease spread through contaminated water, often linked to poor sanitation after disasters like earthquakes.

Economic loss – The financial cost of damage caused by a hazard, including repair, loss of income, and business closures.

Fires – Often caused by broken gas pipes after earthquakes, they are a common secondary hazard.

Food insecurity – When access to sufficient food is disrupted, often due to destroyed crops or damaged supply chains.

Homelessness – A primary effect of building collapse during an earthquake or lava flow during an eruption.

Injury and death – Direct effects of falling buildings, ash falls, pyroclastic flows, and tsunamis linked to tectonic events.

Mercalli scale – Measures the intensity of an earthquake by its observed effects on people and buildings, from I to XII.

Moment Magnitude Scale (MMS) – A scale used to measure the amount of energy released by an earthquake, replacing the Richter scale.

Pyroclastic flow – A fast, hot mix of gas, ash and rock from a volcano that destroys nearly everything in its path.

Respiratory illness – Health conditions such as asthma, which can worsen due to ash inhalation or poor air quality after eruptions.

Secondary hazard – A hazard that follows a primary event, such as landslides or disease outbreaks after a quake.

Tectonic hazard – A natural hazard caused by movement of the Earth’s crust, including earthquakes and volcanic eruptions.

Managing the Impacts of Tectonic Hazards

Disaster response – The immediate actions taken after a hazard, including rescue, medical aid and provision of shelter.

Early warning system – Technology and communication tools that alert people to an imminent hazard, giving them time to act.

Evacuation – The organised movement of people away from danger zones before or after a tectonic event.

GIS (Geographic Information Systems) – Technology used for hazard mapping and planning by analysing spatial data.

Hazard mapping – Identifying and showing areas at greatest risk from earthquakes or eruptions, used for planning responses.

Long-term response – Actions that happen months or years after an event to rebuild and reduce future risk.

Monitoring – The use of equipment like seismometers, tiltmeters and gas sensors to track tectonic activity.

Park’s hazard response curve – A model showing how quality of life changes over time after a disaster, from disruption to recovery.

Planning – Strategies to reduce the risk of hazards, such as land use zoning and emergency supply stockpiling.

Prediction – Estimating when and where a hazard might occur, especially for volcanic eruptions where warning signs are clearer.

Protection – Measures to keep people and buildings safe, such as strengthening structures or excluding people from dangerous areas.

Seismometer – An instrument that records ground movement, helping scientists monitor earthquakes and volcanic activity.

Technology – Tools and methods (e.g. satellite imagery, sensors, communication systems) used to reduce hazard risks.

Earthquake Case Study: Türkiye–Syria

Aftershock – A smaller earthquake that follows the main quake, often causing further damage to already weakened structures.

Arabian Plate – A tectonic plate involved in the Türkiye-Syria earthquake, moving north and causing stress along the fault line.

East Anatolian fault – A transform plate boundary where the 2023 Türkiye-Syria earthquake occurred.

Gaziantep & Kahramanmaraş – Turkish cities that experienced some of the worst damage in the 2023 earthquake.

International aid – Emergency help provided by other countries or global organisations after a disaster.

Magnitude 7.8 – The strength of the main Türkiye-Syria earthquake, one of the most powerful in the region’s recent history.

Shelters and camps – Temporary places for displaced people to stay, especially important in Syria where the conflict limited other housing options.

Stricter building regulations – Laws introduced or strengthened after the earthquake to improve future safety.

UN appeal – A call for international support launched by the United Nations to help those affected by the Türkiye-Syria earthquake.

World bank funding – Financial support provided for Türkiye's recovery and reconstruction after the earthquake.

Volcanic Eruption Case Study: Cumbre Vieja

Banana farms – A major source of income in La Palma; over 400 hectares were destroyed during the 2021 eruption.

Cumbre Vieja – The volcanic ridge on La Palma where the Tajogaite volcano erupted in 2021.

Hot spot – A location in the Earth's crust where magma rises from deep within the mantle, not on a plate boundary.

La Palma – One of the Canary Islands (Spain), where the 2021 volcanic eruption occurred.

Lava flow – Molten rock that erupts from a volcano and flows over the surface, destroying buildings and infrastructure.

Magma plume – A rising column of superheated rock in the mantle that creates volcanic activity above it.

Red alert – The highest level of warning issued during the eruption to signal severe danger.

Tajogaite volcano – The name given to the erupting volcano in the 2021 Cumbre Vieja eruption.

VEI 2–3 – The Volcanic Explosivity Index range of the 2021 eruption, indicating it was moderate in scale but still highly damaging.