Tectonic Hazards

What Tectonic Hazards covers

Tectonic Hazards is examined in AS Unit 1, Changing Landscapes, and again in A2 Unit 4, Contemporary Themes in Geography — the A2 treatment builds on the same content. It covers the internal structure of the Earth, mechanisms of plate movement, divergent and conservative plate margins, convergent margins and subduction, hot spots and the global distribution of tectonic hazards, the hazard profile and measuring magnitude, types of volcano and styles of eruption, primary volcanic hazards, secondary volcanic hazards, impacts of volcanic activity at different scales, contrasting volcanic eruptions, earthquake characteristics and seismic waves, earthquake hazards and ground behaviour, tsunami processes and impacts, contrasting earthquake events, risk, vulnerability and human factors, monitoring, prediction and warning and mitigation, response and the hazard management cycle.

The 18 subtopics

Each one has its own page. WJEC AS Geography students sit this topic in the first year.

• The internal structure of the EarthApproximate radius of the Earth, mohorovičić discontinuity and how seismic waves show that the outer core is liquid.Open →
• Mechanisms of plate movementRidge push, slab pull and typical rate of plate movement.Open →
• Divergent and conservative plate marginsDecompression melting at a spreading ridge, transform fault at a mid-ocean ridge and continental example of a divergent margin.Open →
• Convergent margins and subductionThree kinds of convergent plate margin, why magma is generated above a subducting slab and benioff zone.Open →
• Hot spots and the global distribution of tectonic hazardsHot spot, pacific Ring of Fire and second great earthquake belt after the Ring of Fire.Open →
• The hazard profile and measuring magnitudeNatural hazard, main elements of a hazard profile and range of the Mercalli scale.Open →
• Types of volcano and styles of eruptionApproximate silica content of basaltic magma, shield volcano and two composite volcanoes.Open →
• Primary volcanic hazardsPyroclastic flow, three hazards created by a heavy fall of ash and main gases released by a volcano.Open →
• Secondary volcanic hazardsThree ways a lahar can be triggered, volcanic landslide or sector collapse and eruption that began with the largest landslide ever recorded.Open →
• Impacts of volcanic activity at different scalesTwo demographic impacts of a major eruption, three economic impacts of an eruption on a farming region and local-scale impact of an eruption.Open →
• Contrasting volcanic eruptionsRecall questions on comparing a developed and a developing country's experience of the same year's eruptions, the human and economic costs of each, an island capital destroyed, and why one African volcano is feared above others.Open →
• Earthquake characteristics and seismic wavesFocus of an earthquake, how a P wave travels through rock and motion caused by an S wave.Open →
• Earthquake hazards and ground behaviourGround shaking, why soft sediment increases earthquake damage and city damaged by seismic amplification.Open →
• Tsunami processes and impactsTwo causes of tsunami other than earthquakes, typical open-ocean speed and wavelength for a tsunami and what happens to a tsunami as it approaches the shore.Open →
• Contrasting earthquake eventsDate and magnitude of the Haiti earthquake and date and magnitude of the Tōhoku earthquake.Open →
• Risk, vulnerability and human factorsResilience in the context of tectonic hazards, how the level of economic development affects earthquake deaths and two ways technology reduces vulnerability.Open →
• Monitoring, prediction and warningFour techniques used to monitor a volcano, harmonic tremor and seismic gap theory.Open →
• Mitigation, response and the hazard management cycleFour stages of the hazard management cycle, volcanic event being successfully modified and three features of aseismic building design.Open →

What you need to know

Answer each one before you reveal it.

Take Tectonic Hazards further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Focus vs Epicentre

  Focus: the point underground at which the rupture begins and the energy is released. Epicentre: the point on the surface directly above where that rupture began.

• P wave vs S wave

  P wave: the faster body type, which travels through solid and liquid and pushes material back and forth along its path. S wave: the slower body type, which cannot pass through liquid and moves material at right angles to its path.

• Primary effect vs Secondary effect

  Primary effect: damage caused directly by the ground shaking or the eruption itself. Secondary effect: damage that follows afterwards, such as fire, disease or landslide.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What are the four main layers of the Earth, working inwards from the surface?

   Model answer

   The crust, the mantle, the outer core and the inner core.

2. 2

   State the approximate radius of the Earth.

   Model answer

   It is about 6,371 km from the surface to the centre.

3. 3

   What is the Mohorovičić discontinuity?

   Model answer

   It is the boundary between the base of the crust and the top of the mantle, detected because seismic waves speed up sharply as they cross it.

4. 4

   How does the thickness of continental crust compare with that of oceanic crust?

   Model answer

   Continental crust is roughly 30 to 70 km thick, while oceanic crust is only about 6 to 10 km thick.

5. 5

   Why is oceanic crust denser than continental crust?

   Model answer

   Oceanic crust is basaltic and rich in iron and magnesium at about 3.0 g cm⁻³, whereas continental crust is granitic and richer in silica and aluminium at about 2.7 g cm⁻³.

6. 6

   Why is no oceanic crust older than about 200 million years when continental crust can be billions of years old?

   Model answer

   Oceanic crust is continually destroyed by subduction, while continental crust is too buoyant to be carried down and so survives.

What is inside Levo

Six ways to work the same material.

Tectonic Hazards revision questions

Is Tectonic Hazards examined at AS in WJEC Geography?

Yes. It sits in AS Unit 1 and A2 Unit 4, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.

What does Tectonic Hazards cover in WJEC AS-Level Geography?

18 subtopics: the internal structure of the earth, mechanisms of plate movement, divergent and conservative plate margins, convergent margins and subduction, hot spots and the global distribution of tectonic hazards, the hazard profile and measuring magnitude, types of volcano and styles of eruption, primary volcanic hazards, secondary volcanic hazards, impacts of volcanic activity at different scales, contrasting volcanic eruptions, earthquake characteristics and seismic waves, earthquake hazards and ground behaviour, tsunami processes and impacts, contrasting earthquake events, risk, vulnerability and human factors, monitoring, prediction and warning and mitigation, response and the hazard management cycle. Each one has its own page with questions and model answers.

How is Tectonic Hazards organised?

By the WJEC 601-8455-3 specification, subtopic by subtopic, so it matches the order you are taught it in.