A lahar is a fast-moving flow of volcanic ash and debris mixed with water. The consistency is like wet concrete, and lahars follow river valleys for tens of kilometres.

Describe the Nevado del Ruiz lahar of 1985.

A small eruption on 13 November 1985 melted part of the ice cap on Nevado del Ruiz in Colombia. Lahars buried the town of Armero, and estimates made soon afterwards put the toll near 23,000.

Why was Armero so badly affected despite a small eruption?

Warnings had been issued but were not acted on, and the town lay on old lahar deposits in a valley. The lahar arrived after dark, more than two hours after the eruption.

What is a jökulhlaup and what triggers one?

A jökulhlaup is a sudden glacial outburst flood caused by an eruption beneath an ice cap. Meltwater collects under the ice and then bursts out as a torrent.

Eduqas A-Level Geography A110QS

Coastal LandscapesLandscape

Topic overview The coast as a system: inputs, outputs, stores and transfers Sediment sources, sediment cells and dynamic equilibrium Tides, currents and wave types High and low energy coastal environments Fetch, wave refraction and wave reflection Lithology and structural geology at the coast Sub-aerial weathering and mass movement at the coast Marine erosion processes Cliffs, wave-cut platforms, geos and blowholes Headlands, bays and the cave to stump sequence Coastal transport and longshore drift Coastal deposition, flocculation and sediment sorting Beaches, spits and bars Tombolos, cuspate forelands and sandy coastlines Coastal sand dunes and aeolian processes Estuarine coastlines, tidal flats and salt marshes Coral reefs and mangrove coastlines Storms, seasons and sea level change Coastal processes and human activity Human impacts and coastal management

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Changing Places

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Water and Carbon Cycles

Topic overview Systems, mass balance and the water balance Global water stores, their size and residence times Changing stores: sea level change and cryospheric processes The drainage basin as an open system Precipitation inputs and interception Infiltration, overland flow and throughflow Percolation, groundwater flow, channel flow and basin outputs River regimes and the factors that control them The storm hydrograph: components and shape Climatic factors influencing storm hydrographs Catchment factors influencing storm hydrographs Cloud formation and theories of precipitation Excess runoff: natural and human causes Deficit in the water cycle and aquifer recharge The global carbon cycle: stores, fluxes and mass balance Fast carbon pathways between land and atmosphere Ocean and atmosphere exchange and the slow carbon cycle Carbon stores in tropical rainforest and temperate grassland Land-use change and the carbon store Peatlands and the changing carbon store Rising atmospheric carbon, the energy budget and its impacts Feedback, thresholds and permafrost thaw

Global Migration

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Global Governance of the Oceans

Topic overview Supranational institutions and the law of the sea Maritime zones from the baseline to the high seas Chokepoints, canals and piracy in maritime trade Britain's maritime past and the Commonwealth Container shipping, oil tankers and shipping regulation Smuggling and people trafficking at sea Seafloor data cables: growth, patterns and uses Risks to seafloor cables and international protection Ownership of ocean resources and contested sovereignty Unequal access: landlocked states and indigenous coastal peoples The Global Commons and over-exploitation of marine ecosystems Sustainable management: quotas, no-catch zones and conservation zones Sources and consequences of ocean pollution Managing marine waste and the scales of ocean governance

Tectonic Hazards

Topic overview Earth's internal structure and plate movement Divergent plate margins Convergent margins, subduction and collision Conservative margins and hot spots Global distribution of tectonic hazards The hazard profile and magnitude scales Types of volcano and styles of eruption Primary volcanic hazards Secondary volcanic hazards Impacts of volcanic activity at local, regional and global scales Contrasting volcanic eruptions Earthquake characteristics and seismic waves Ground shaking, liquefaction and landslides Tsunami generation and impacts Impacts of earthquakes in contrasting contexts Human factors affecting risk and vulnerability Monitoring, prediction and warning Mitigation and the hazard management cycle

EcosystemsContemporary theme

Topic overview The value of ecosystems: goods and services Global distribution of biomes and its climatic controls The ecosystem concept, energy flow and trophic levels Nutrient cycling and the Gersmehl model Contrasting nutrient cycles: tropical rainforest and taiga Net primary productivity and limiting factors Measuring biodiversity Threats to biodiversity from local to global scale Tropical rainforests and coral reefs at risk Wetlands at risk Conserving biodiversity: strategies, priorities and funding Succession, seres and the climatic climax Sub-climax and plagioclimax communities The Arctic tundra: climate, soils, plants and animals Impacts of climate change on the Arctic tundra Sustainable use and management of the Arctic tundra

Economic Growth and Challenge: IndiaContemporary theme

Topic overview Relief and drainage patterns of India India's climate and the monsoon Water availability and water stress Population distribution, growth and structure Governance, health, education and welfare Caste, gender and cultural influences Resources, relief and climate as opportunity and constraint Droughts, floods and climate variability Economic activity, democracy and the role of government The changing size and structure of India's economy Global shift, outsourcing and offshoring India's soft power and global governance Environmental pressures of economic growth Water, food and energy security and urban pressures Sustainable development strategies in India

Economic Growth and Challenge: ChinaContemporary theme

Topic overview Relief and drainage patterns of China China's climate and the monsoon Water availability and the north-south imbalance Population distribution, growth and structure Governance, health, education and welfare Gender and minority groups in China Resources, relief and climate as opportunity and constraint Droughts, floods and climate variability Economic activity, modified communism and the role of government The changing size and structure of China's economy Global shift, offshoring and the workshop of the world China's soft power and global governance Environmental pressures of economic growth Water, food and energy security and urban pressures Sustainable development strategies in China

Development in an African ContextContemporary theme

Topic overview Changing definitions of development Simple, composite and qualitative measures of development The development gap and the development continuum Regional, ethnic and gender variation within countries The resource base: minerals and energy Soils, relief, climate and water availability Climate variability, drought and flood Free trade, trade blocs and protectionism The resource curse and conflict minerals MNCs, foreign direct investment and offshoring Tourism and fair trade Colonialism, neo-colonialism, governance and corruption Education, health, welfare and the position of women The environmental costs of development Desertification in the Sahel Strategies to promote development

Energy Challenges and DilemmasContemporary theme

Topic overview Classifying energy resources Fossil fuel stocks, reserves and their global distribution Geological factors in energy supply Insolation, wind strength and reliability Relief, dam sites and hydroelectric power Waves, tides and biofuels: favourable locations Changing global patterns of energy demand Economic and technological influences on energy demand Transfers, storage and the pricing of oil and gas OPEC, national governments and the oil and gas companies Environmental problems of energy extraction, transport and use Political, economic and technological problems of energy Appropriate technology and micro-generation in developing countries National energy mixes and world energy prices Demand reduction and energy efficiency policies Clean fossil fuel technologies and the sustainability of alternatives

Weather and ClimateContemporary theme

Topic overview Structure of the atmosphere The atmospheric heat budget Global atmospheric circulation and the tricellular model Pressure belts and planetary surface winds Oceanic circulation, continentality and altitude The world's major climate types The ITCZ and seasonal migration The monsoon climate The climate of the UK Air masses affecting the UK The jet stream and UK weather ENSO and short-term climate change Vulnerability, resilience and adaptive capacity Hazards of low- and high-pressure systems and their management Urban climates and air quality Climate change: shifting belts, tipping points and response

Geographical Skills

Topic overview Grid references, coordinates and locating a place Distance, area, direction and scale Sampling and sources of error Percentages, ratios, densities and frequencies Measures of central tendency Measures of dispersion Concentration, ratios and development indices Correlation and Spearman Rank Chi-square and significance testing Mapping techniques Graphs and diagrams Digital and qualitative field techniques

Tectonic Hazards

Secondary volcanic hazards

3 things to know
Component 3 Section A

Overview

Secondary volcanic hazard, how a lahar forms and jökulhlaup and what triggers one.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Define a secondary volcanic hazard.

Key term

What is a lahar?

Key term

Explain how a lahar forms.

Questions from this subtopic

Each one with the model answer underneath.

1
Define a secondary volcanic hazard.
Model answer
A secondary volcanic hazard arises from the effects of an eruption rather than from the eruption itself. Lahars, glacial floods, landslides, tsunami and climatic change are examples.
2
What is a lahar?
Model answer
A lahar is a fast-moving flow of volcanic ash and debris mixed with water. The consistency is like wet concrete, and lahars follow river valleys for tens of kilometres.
3
Explain how a lahar forms.
Model answer
Heavy rain, melting snow or a breached crater lake saturates loose ash on a volcano's flanks. The mixture then flows downslope, picking up more debris as it goes.
4
Describe the Nevado del Ruiz lahar of 1985.
Model answer
A small eruption on 13 November 1985 melted part of the ice cap on Nevado del Ruiz in Colombia. Lahars buried the town of Armero, and estimates made soon afterwards put the toll near 23,000.
5
Why was Armero so badly affected despite a small eruption?
Model answer
Warnings had been issued but were not acted on, and the town lay on old lahar deposits in a valley. The lahar arrived after dark, more than two hours after the eruption.
6
What is a jökulhlaup and what triggers one?
Model answer
A jökulhlaup is a sudden glacial outburst flood caused by an eruption beneath an ice cap. Meltwater collects under the ice and then bursts out as a torrent.

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