Why can volcanic eruptions be predicted when earthquakes cannot?

Magma gives days or weeks of measurable warning as it forces its way towards the surface, whereas the fracture that starts an earthquake gives no reliable signal before it happens.

Name four techniques used to monitor a volcano.

Seismometers to detect magma movement, tiltmeters and satellite radar to measure ground deformation, gas spectrometers to sample the emissions, and thermal imaging to detect heating of the ground.

What is harmonic tremor, and what does it indicate?

Harmonic tremor is a continuous rhythmic vibration rather than a sharp shock, and it indicates magma and gas moving through the plumbing of the volcano.

Why do volcanologists watch for changes in sulphur dioxide emissions?

A rising proportion of sulphur dioxide suggests that fresh magma is close to the surface, because that gas only comes out of solution at shallow depth.

How does ground deformation give warning of an eruption?

Magma filling a shallow chamber makes the flanks of the volcano bulge measurably, and tiltmeters and satellite radar can detect that long before there is anything to see.

WJEC A-Level Geography 601-8455-3

Coastal Landscapes

Glaciated Landscapes

Topic overview The glacier as an open system Climate change and the glacier budget Glacier movement Types of ice mass and their distribution Glacial weathering and erosion processes Macro-scale erosional landforms Glacial transport and depositional landforms Fluvioglacial landforms Suites of landforms in glacial landscapes Periglacial processes and ground ice Periglacial action of water and wind Glacial change over different timescales Glacial environments and human activity

Tectonic Hazards

Topic overview 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 Mitigation, response and the hazard management cycle

Changing Places

Topic overview What gives a place its character Flows and connections that shape places Meaning, perception and attachment to place How places are represented Economic restructuring and the Clark Fisher model Deindustrialisation and social inequality The service economy and its impacts The knowledge economy and clusters Rebranding rural places Managing change in rural places Rebranding urban places Managing change in urban places Comparing a home place with a contrasting place How place change affects people's lives

Water and Carbon Cycles

Topic overview The water cycle as a global system and mass balance Global water stores and residence times Cryospheric processes and sea-level change Drainage basin inputs, stores and outputs Flows within the drainage basin River regimes and their controls Storm hydrographs and hydrograph shape Air uplift, cloud formation and precipitation Excess runoff and flooding Deficit in the water cycle and aquifer recharge The global carbon cycle and its stores Carbon pathways between land and the atmosphere Carbon transfers involving the oceans Carbon stores in biomes and land-use change Changing carbon stores in peatlands Rising atmospheric carbon and its impacts Feedback within and between the water and carbon cycles

Global Migration

Topic overview Globalisation and a shrinking world Classifying and mapping migration Causes of international economic migration Consequences and management of economic migration Refugee movements and internal displacement Rural-urban migration in developing countries Superpowers and global hub cities Migration policy and public debate in the UK Managing refugee crises Informal settlements in developing cities

Global Governance of the Oceans

Topic overview Supranational institutions and global governance Laws and agreements governing the oceans Strategic value of the oceans and maritime security Shipping, cables and illicit flows Sovereignty over ocean resources Managing marine environments Ocean pollution and its management Governance across scales: an ocean case study

EcosystemsContemporary theme

Topic overview The value of ecosystems to people The distribution of global biomes Ecosystem structure, energy flow and productivity Nutrient cycling in contrasting biomes Measuring and threatening biodiversity Conserving biodiversity Succession and local ecosystems The Arctic tundra biome Sustainable use of the Arctic tundra

Economic Growth and Challenge: IndiaContemporary theme

Topic overview India's relief, drainage and climate India's population, society and governance India's resources, hazards and economic geography India's global role and economic growth Environmental pressures of India's growth Sustainable development strategies in India

Economic Growth and Challenge: ChinaContemporary theme

Topic overview China's relief, drainage and climate China's population, society and governance China's resources, hazards and economic geography China's global role and economic growth Environmental pressures of China's growth Sustainable development strategies in China

Development in an African ContextContemporary theme

Topic overview Defining and measuring development Physical factors influencing development Economic factors influencing development Political, social and cultural factors in development The environmental cost of development Desertification Strategies to promote development

Energy Challenges and DilemmasContemporary theme

Topic overview Classifying and distributing energy resources Physical factors in energy supply The changing demand for energy Managing oil and gas globally Problems of extraction, transport and use Energy mixes and development Sustainable solutions to energy demand

Weather and ClimateContemporary theme

Topic overview Structure of the atmosphere and the heat budget Global atmospheric and oceanic circulation The world's major climate types Weather and climate of Wales and the UK Extreme weather and ENSO Hazards of low and high pressure systems Urban climates and air quality People, climate and the future

Fieldwork and Geographical Skills

Topic overview The six-stage enquiry process Sampling and data collection Presenting geographical data Statistical analysis of geographical data Fieldwork techniques and apparatus Map skills: grid references, latitude and longitude, scale and direction

Key Concepts in Geography

Topic overview Systems, equilibrium and feedback Causality, interdependence and mitigation Resilience, risk and sustainability Place, space, scale and representation

Tectonic Hazards

Monitoring, prediction and warning

2 things to know
AS Unit 1 and A2 Unit 4

Overview

Four techniques used to monitor a volcano, harmonic tremor and seismic gap theory.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Why did the Pacific have a tsunami warning system decades before the Indian Ocean did?

Key term

Distinguish prediction from forecasting.

Questions from this subtopic

Each one with the model answer underneath.

1
Distinguish prediction from forecasting.
Model answer
A prediction states when and where a specific event will happen, while a forecast gives the probability of an event occurring within a stated period and area.
2
Why can volcanic eruptions be predicted when earthquakes cannot?
Model answer
Magma gives days or weeks of measurable warning as it forces its way towards the surface, whereas the fracture that starts an earthquake gives no reliable signal before it happens.
3
Name four techniques used to monitor a volcano.
Model answer
Seismometers to detect magma movement, tiltmeters and satellite radar to measure ground deformation, gas spectrometers to sample the emissions, and thermal imaging to detect heating of the ground.
4
What is harmonic tremor, and what does it indicate?
Model answer
Harmonic tremor is a continuous rhythmic vibration rather than a sharp shock, and it indicates magma and gas moving through the plumbing of the volcano.
5
Why do volcanologists watch for changes in sulphur dioxide emissions?
Model answer
A rising proportion of sulphur dioxide suggests that fresh magma is close to the surface, because that gas only comes out of solution at shallow depth.
6
How does ground deformation give warning of an eruption?
Model answer
Magma filling a shallow chamber makes the flanks of the volcano bulge measurably, and tiltmeters and satellite radar can detect that long before there is anything to see.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Coastal Landscapes

Glaciated Landscapes

Tectonic Hazards

Changing Places

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Governments must win votes.

ruralurbanelite

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AFew coastal people recognised the signs.

BThe coasts were densely populated.

CMany communities were struck with no notice at all.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

The Mariana Trench reaches almost 11,000 m below sea level.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Tectonic Hazards, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.