The causes and types of volcano, their effects, why people live near them, and how the hazard is managed (AO1, AO2).

What this dot point is asking

CCEA wants you to explain how volcanoes form, the difference between the two main types, the effects of an eruption, why people live near volcanoes despite the danger, and how the hazard is managed. As with earthquakes, organise effects into social, economic and environmental. The "why live there" question is distinctive to volcanoes and rewards a list of real benefits set against the risk.

How volcanoes form

The two types of volcano

The lava type controls the shape and the violence of the eruption.

• Shield volcano. Built from runny, basaltic lava that flows far before cooling, giving gentle, wide slopes. It forms at constructive margins and hotspots, and erupts frequently but gently. Example: Mauna Loa, Hawaii.
• Composite (strato) volcano. Built from alternating layers of thick, sticky lava and ash, giving steep, tall cones. It forms at destructive margins and erupts less often but violently and explosively, often with deadly ash clouds and pyroclastic flows. Example: Mount Etna, Italy.

The effects of an eruption

Organise the effects under three headings.

• Social impacts (on people): deaths from lava, ash and pyroclastic flows, people made homeless, and breathing problems and contaminated water from ash.
• Economic impacts (on money and jobs): destroyed homes, farmland and infrastructure, lost tourism and trade, disrupted air travel from ash clouds, and high clean-up costs.
• Environmental impacts (on nature): land buried by lava and ash, fires, polluted air and water, but also, in time, new, fertile land.

Why people live near volcanoes

Managing the volcanic hazard

Eruptions can often be predicted better than earthquakes, so monitoring is central.

• Monitoring and prediction. Seismometers detect tremors as magma rises, gas sensors detect changing emissions, and tiltmeters detect the ground bulging. Together these can warn of an eruption days ahead.
• Warnings and evacuation. Clear warning systems and evacuation plans move people out of danger before an eruption.
• Hazard mapping and land use. Hazard maps show areas at risk from lava, ash and flows, so building is kept away from the most dangerous zones.

Worked example: the "why live there" question

Common mistakes

Examples in context

Example 1. Iceland turning a hazard into a resource. Iceland sits on the Mid-Atlantic Ridge, so volcanic and geothermal heat are abundant. Rather than only suffering the hazard, Iceland taps the heat to generate almost all its electricity and to heat homes and greenhouses, even bathing in the warm water of the Blue Lagoon. This shows how the geothermal benefit can outweigh the risk and supports the "why live there" answer with a real place.

Example 2. When ash grounds aircraft. When an Icelandic volcano erupted in 2010, its ash cloud spread across Europe and grounded thousands of flights for days, because volcanic ash can damage jet engines. This was a major economic impact felt far from the volcano itself, showing how an eruption's effects can be widespread, not just local, which is a strong point in an effects answer.

Try this

Q1. Give one difference between a shield volcano and a composite volcano. [2 marks]

• Cue. Shield: gentle, wide, runny lava, gentle eruptions. Composite: steep cone, sticky lava and ash, violent eruptions.

Q2. Give two reasons people live near volcanoes. [2 marks]

• Cue. Any two: fertile soils, geothermal energy, tourism and jobs, minerals, or cannot afford to move.

Q3. Name one method used to monitor a volcano. [1 mark]

• Cue. Seismometers, gas sensors or tiltmeters (detecting ground bulging).