How does magma temperature affect eruption style?

Hotter magma is less viscous and tends to produce effusive eruptions; cooler magma is more viscous and can be more explosive.

How does high silica content affect magma viscosity?

High silica content increases viscosity, making the magma thick and resistant to flow.

Why can gases not escape easily from high-silica magma?

The high viscosity traps gases within the magma.

Edexcel A-Level Geography 9GE0

Tectonic Processes and Hazards

Topic overview Global distribution of tectonic hazards and plate boundary processes The structure of the Earth and mantle convection Ridge push, slab pull and sea-floor spreading Destructive and constructive plate margins Collision and transform margins Magma composition and eruption style The Benioff zone and earthquake magnitude Seismic waves and their effects Volcanic hazards and tsunamis Hazard, vulnerability, resilience and the risk equation The Pressure and Release model The impacts of tectonic hazards Measuring hazards, and the hazard profile Speed of onset, areal extent, duration and predictability Why impacts differ between countries Education, buildings, healthcare and income as factors in vulnerability Governance at local and national level Population density, isolation and urbanisation How development level shapes disaster outcomes Trends in tectonic disasters, data reliability and sampling Mega-disasters and multiple-hazard zones Theoretical frameworks for prediction, impact and management Land-use zoning and hazard-resistant design Monitoring, prediction, preparedness and aid

Glaciated Landscapes and ChangeLandscape

Topic overview The cryosphere and the types of glacier Glacial chronology and the causes of climate change Evidence for Pleistocene ice extent Relict glacial landscapes, and polar against temperate glaciers Permafrost, nivation, frost heave and solifluction Ice wedges, patterned ground, pingos and loess Glacial mass balance and the ice-albedo feedback Accumulation and ablation processes The equilibrium line and how glaciers move What controls the rate of glacial movement Basal slip and internal deformation What speeds a glacier up or slows it down Debris entrainment, transport and the scale of glacial landforms Glacial erosion, corries, aretes and pyramidal peaks Troughs, hanging valleys, ribbon lakes and roches moutonnees Moraines: lateral, medial, recessional and terminal Drumlins, till plains and the two kinds of till Erratics and reconstructing former ice movement Meltwater pathways, and analysing fluvioglacial sediment Fluvio-glacial (meltwater) landforms The value of glaciated landscapes to people Natural hazards and human threats to glaciated landscapes Climate change and the players who manage these landscapes Management approaches, legislation and scale

Coastal Landscapes and ChangeLandscape

Topic overview The littoral zone and the influences that shape it Concordant and discordant coasts, and geological structure Coastal types and the influence of rock structure Faulting, folding and geological weaknesses Rock type, permeability and cliff profiles Psammosere succession on sand dunes Halosere succession and rates of recession Waves, beach profiles and marine erosion Wave-cut notches, platforms and cliffs Caves, arches, stacks and stumps Longshore drift and the transport of sediment Spits, bars, tombolos and other depositional landforms Sediment cells: sources, transfers and sinks Weathering on the coast Mass movement and its landforms Rapid coastal recession and variations in its rate Causes of sea level change, and emergent coastlines Submergent coastlines and contemporary sea level rise Coastal flooding as a significant and increasing risk Losses from coastal recession, and environmental refugees Hard and soft engineering on the coast Integrated coastal zone management and shoreline policies How coastal management decisions are made, and by whom Using GIS, photographs and crowd-sourced data in coastal management

Globalisation

Topic overview Widening, deepening and the global flows The five global flows defined Transport, ICT and the shrinking world Political and economic decision making in globalisation Measuring globalisation: the AT Kearney and KOF indices TNCs, glocalisation, outsourcing and switched-off places The global shift and who gains from it The social and environmental costs of the global shift Deindustrialised regions in developed countries Rural-urban migration and the growth of megacities Global hub cities and international migration The costs and benefits of economic migration Cultural diffusion and the spread of a global culture Cultural erosion and opposition to globalisation Measuring development: GDP, HDI and the Gender Inequality Index Environmental measures, the Gini coefficient and the Lorenz curve Geographical skills: statistics, data and research ethics Winners, losers and the widening development gap Social, political and environmental tensions from global change Local sourcing and its costs and benefits Fair trade, ethical consumption and recycling

Regenerating PlacesPlaces

Topic overview Economic classification and variation from place to place The functions of a place and why they change Measuring place change and deprivation Past and present connections shaping economic and social characteristics Economic and social inequalities changing perceptions of areas Lived experience, attachment and conflict over place Evidence, representations, Spearman's rank and significance testing Measures of dispersion: range, interquartile range and standard deviation Successful regions and the spiral of decline Perceptions of the need for regeneration National planning, transport and funding decisions National policy: Levelling Up, house-building targets and foreign investment Local government incentives and inward investment What attracts investment, and the multiplier effect Local interest groups and tourism, sport and rural regeneration Rebranding to change public perception of places Rebranding deindustrialised cities and rural areas Economic, social and environmental measures of success Deprivation domains and demographic change How different stakeholders judge regeneration Urban stakeholders and their criteria for success Urban regeneration: reality, image and contested decisions Rural stakeholders and their criteria for success Rural regeneration: reality, image and contested decisions

Diverse PlacesPlaces

Topic overview Population structure variation from place to place and over time Population characteristics variation from place to place and over time Global, national and regional influences on place How places are represented in film, art, music and media Continuity and change in demographic and cultural character Urban places viewed differently by different groups Idyllic and negative perceptions of rural places How reputation, media and lived experience shape rural views Evidence about living spaces, and research ethics Media and creative sources, coding and sampling Increasing cultural and social diversity in the UK What causes segregation Segregation along the rural-urban continuum, and migration Perceptions of segregated places, and measuring segregation Land-use change and tension between residents and newcomers Measuring integration, and community cohesion in Slough Diverse rural communities: the Lake District

The Water Cycle and Water Insecurity

Topic overview The processes of the hydrological cycle The stores of water and their relative size Fluxes, residence time, fossil water and the cryosphere The drainage basin as an open system What influences drainage basin processes Water budgets and river regimes What shapes a storm hydrograph Reading a storm hydrograph Meteorological and hydrological drought, ENSO and human causes The impacts of drought on wetlands and forests The physical causes of flooding Human causes of flooding The environmental and economic impacts of flooding Social impacts, case studies and synoptic charts How climate change alters the hydrological cycle ENSO, uncertainty and future projections Water stress, scarcity and the physical causes of insecurity Human causes of water insecurity and rising demand Physical and economic water scarcity Why economic scarcity happens, and the price of water How water is used: industry, energy and agriculture The consequences of water insecurity Competing users and trans-boundary rivers The players in water conflict, and its causes Water transfers as a hard engineering solution Mega dams and their costs Desalination, and the case against the techno-fix The value of more sustainable schemes of restoration of water supplies and water conservation Integrated drainage basin management and water treaties The players in water management and the conflicts between them

The Carbon Cycle and Energy Security

Topic overview Carbon stores and fluxes Chemical weathering, carbonate rocks and the slow carbon cycle Biological processes sequestering carbon (fast carbon cycle)Balanced carbon cycle sustaining earth systems Energy security and measuring energy use What shapes a country's energy mix Contrasting energy mixes, public perception and OPEC The players in energy security, and energy pathways Energy pathways and the mismatch between supply and demand Unconventional fossil fuels and their environmental cost Renewables and nuclear: the costs and benefits Biofuels, carbon capture, hydrogen and the uncertainties Land-use change and its effect on the carbon and water cycles Ocean acidification and coral reefs Climate belts, Amazonian drought and ecosystem services Forest loss, the Kuznets curve and consumer attitudes How warming changes the hydrological cycle Uncertainty, ocean health and vulnerable regions Uncertainty, feedback loops and tipping points Adaptation and mitigation strategies Why players disagree, and handling climate data

Superpowers

Topic overview What makes a superpower: economy, politics and military Cultural, demographic and resource characteristics Hard power, soft power and smart power The Belt and Road Initiative, and power indexes Patterns of power change over time Emerging powers and how their strengths are assessed World systems, dependency and modernisation theory IGOs and how superpowers dominate them TNCs, cultural influence and Westernisation How superpowers and emerging nations act in global decisions Alliances, IGOs and geostrategy The environmental cost of superpower demand The rising middle class in emerging superpowers Contested resources and intellectual property Contested political spheres and open conflict China's ties with the developing world Tensions in Asia and the Middle East Challenges to existing superpowers, and future power structures

Health, Human Rights and InterventionConnections

Topic overview Concepts of human development What causes variations in health and life expectancy Health variations within countries Governments and IGOs defining development targets and policies Human rights in international law and agreements Differences between countries in definitions and protection of human rights Variations in rights within countries Progress towards equality, and the case studies Forms of geopolitical intervention Development aid and the arguments about it Economic development projects and military aid Development focused on human rights and welfare Health and life expectancy variation between and within countries Welfare states, neo-liberalism and IGO programmes The Responsibility to Protect and UN authorisation Military alliances, war crimes and the cost of military power Measuring the success of geopolitical interventions The mixed record of development aid Why superpowers give aid, and the Gini coefficient Military interventions, both direct and indirect, have a mixed record of success

Migration, Identity and SovereigntyConnections

Topic overview Globalisation and the growth of migration What changes migration patterns, and flow-line maps Varied and complex causes of migration Consequences of international migration Nation states and their varied histories Nationalism in the development of the modern world Tax havens, new state forms and alternatives to capitalism The UN and its interventions The IMF, World Bank, WTO and other IGOs Migration in a globalised world Open borders, deregulation and migrant integration Nation states, borders and contested territory Nationalism, decolonisation and low-tax regimes IGOs managing environmental problems National identity as an elusive and contested concept Challenges to national identity Consequences of disunity within nations

Tectonic Processes and Hazards

Magma composition and eruption style

3 things to know
Papers 1 and 3

Overview

Recall questions on how silica content, gas and temperature decide whether an eruption is effusive or explosive.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

How does silica content affect volcanic eruption characteristics?

Key term

How does magma viscosity influence volcanic eruption style?

Key term

How does gas content influence volcanic eruption magnitude?

Questions from this subtopic

Each one with the model answer underneath.

1
How does magma viscosity influence volcanic eruption style?
Model answer
High viscosity magma resists flow and tends to produce explosive eruptions; low viscosity magma flows easily and produces effusive eruptions.
2
How does silica content affect volcanic eruption characteristics?
Model answer
High silica content increases viscosity and explosivity; low silica content produces more fluid, effusive eruptions.
3
How does gas content influence volcanic eruption magnitude?
Model answer
Higher gas content increases pressure within the magma, potentially leading to more explosive eruptions.
4
How does magma temperature affect eruption style?
Model answer
Hotter magma is less viscous and tends to produce effusive eruptions; cooler magma is more viscous and can be more explosive.
5
How does high silica content affect magma viscosity?
Model answer
High silica content increases viscosity, making the magma thick and resistant to flow.
6
Why can gases not escape easily from high-silica magma?
Model answer
The high viscosity traps gases within the magma.

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