Tectonic Hazards » Volcanic Hazards

What you'll learn this session

Study time: 30 minutes

The causes and formation of volcanoes
Different types of volcanic eruptions and their characteristics
Primary and secondary effects of volcanic hazards
Responses to volcanic eruptions (immediate and long-term)
Case studies of contrasting volcanic events
How prediction, protection and preparation can reduce impacts

Introduction to Volcanic Hazards

Volcanoes are one of Earth's most spectacular and dangerous natural phenomena. They form when molten rock (magma) from beneath the Earth's crust rises to the surface. When this happens, we call it a volcanic eruption, which can range from gentle lava flows to explosive events that devastate large areas.

Key Definitions:

Volcano: An opening in the Earth's crust through which magma, ash and gases erupt.
Magma: Molten rock beneath the Earth's surface.
Lava: Magma that has reached the Earth's surface.
Pyroclastic flow: Fast-moving currents of hot gas and volcanic matter that flow down the sides of a volcano during an eruption.
Ash cloud: A cloud of ash formed during a volcanic eruption that can travel thousands of kilometres.

How Volcanoes Form

Volcanoes typically form at the boundaries between tectonic plates - the massive sections of Earth's crust that slowly move over the mantle below.

🌋 Convergent Boundaries

When two plates collide and one slides beneath the other (subduction), the descending plate melts in the mantle. This creates magma that rises to form volcanoes. Examples include the volcanoes of the Pacific "Ring of Fire".

💧 Divergent Boundaries

When plates move apart, magma rises to fill the gap, creating new crust and sometimes volcanoes. The Mid-Atlantic Ridge is an example, with Iceland sitting directly on this boundary.

🌌 Hot Spots

Some volcanoes form away from plate boundaries over "hot spots" - areas where magma rises from deep within the mantle. The Hawaiian Islands formed this way as the Pacific Plate moved over a hot spot.

Types of Volcanic Eruptions

Not all volcanic eruptions are the same. The type of eruption depends on the magma's composition, particularly its silica content, gas content and temperature.

🔥 Explosive Eruptions

High silica content makes magma thick and sticky (viscous), trapping gases. When pressure builds up enough, explosive eruptions occur. These produce ash clouds, pyroclastic flows and volcanic bombs. Examples include Mount St. Helens (USA) and Mount Pinatubo (Philippines).

💦 Effusive Eruptions

Low silica content creates runny (less viscous) magma that allows gases to escape easily. These eruptions tend to produce flowing lava rather than explosions. Hawaii's volcanoes typically have effusive eruptions with spectacular lava flows.

Volcanic Hazards and Their Effects

Volcanic eruptions can cause numerous hazards that affect people and the environment in different ways.

Primary Effects (immediate impacts during the eruption)

Lava flows: Destroy buildings and infrastructure, but move slowly enough that they rarely cause fatalities.
Pyroclastic flows: Fast-moving clouds of hot gas and volcanic matter that can travel at speeds up to 700 km/h and reach temperatures of 1,000°C. These are often deadly.
Ash falls: Can collapse roofs, damage crops, contaminate water supplies and cause respiratory problems.
Volcanic bombs: Large chunks of lava ejected from the volcano that solidify in the air and can cause impact damage and fires.
Toxic gases: Including carbon dioxide and sulphur dioxide, which can cause breathing difficulties and, in high concentrations, death.

Secondary Effects (occurring after the main eruption)

Lahars: Mudflows caused when volcanic ash and debris mix with water (often from melted snow or heavy rain).
Landslides: Can occur when volcanic activity destabilises slopes.
Climate effects: Large eruptions can release enough ash and gases into the atmosphere to temporarily cool global temperatures.
Economic impacts: Disruption to agriculture, tourism and transportation (especially air travel due to ash clouds).
Disease: Water contamination and poor living conditions in evacuation centres can lead to disease outbreaks.

Case Study: Mount Pinatubo, Philippines (1991)

Background: After 500 years of dormancy, Mount Pinatubo erupted in June 1991 in one of the largest volcanic eruptions of the 20th century.

Primary effects:

Ejected 10 billion tonnes of magma and 20 million tonnes of sulphur dioxide
Created an ash cloud 35km high
Pyroclastic flows extended 16km from the volcano
847 people died (relatively low due to evacuation)

Secondary effects:

Lahars continued for years after the eruption, triggered by monsoon rains
Global temperatures dropped by about 0.5°C for two years
Agricultural land was covered in ash, affecting food production
200,000 people became homeless

Responses:

Successful evacuation of 200,000 people before the main eruption
International aid of $241 million
Lahar warning systems installed
Dams and channels built to control lahars

Responses to Volcanic Eruptions

How communities and governments respond to volcanic eruptions depends on various factors, including the country's level of development, preparation and resources.

🕐 Immediate Responses

Evacuation of at-risk areas
Search and rescue operations
Emergency medical care
Provision of temporary shelter, food and clean water
Clearing ash from essential infrastructure

📅 Long-term Responses

Rebuilding homes and infrastructure
Economic recovery programs
Improving monitoring systems
Developing better evacuation plans
Land use planning to reduce future risk

Managing Volcanic Hazards

While we can't prevent volcanoes from erupting, we can reduce their impact through prediction, protection and preparation.

🔍 Prediction

Monitoring ground deformation
Measuring gas emissions
Detecting seismic activity
Tracking temperature changes
Using satellite imagery

🛡 Protection

Building diversion channels for lava/lahars
Constructing barriers
Strengthening buildings against ash fall
Land use zoning to limit development in high-risk areas

📝 Preparation

Developing evacuation plans
Public education campaigns
Emergency drills
Stockpiling emergency supplies
Training emergency responders

Case Study: Eyjafjallajökull, Iceland (2010)

Background: This eruption was relatively small but had massive impacts due to its ash cloud disrupting European air travel.

Primary effects:

Limited local damage in Iceland
Ash plume reached 9km into the atmosphere
Melted ice caused flooding (jökulhlaup)

Secondary effects:

Airspace closed across Europe for 6 days
Over 100,000 flights cancelled
10 million passengers stranded
Estimated economic loss of £1.1 billion to the airline industry
Impacts on global supply chains and businesses dependent on air freight

Responses:

Development of better ash detection systems
Revision of aviation protocols for volcanic ash
Improved international coordination for similar events

Comparing Volcanic Hazard Impacts

The impacts of volcanic eruptions vary significantly between high-income countries (HICs) and low-income countries (LICs).

📈 HICs (e.g., Japan, Iceland)

Better monitoring and early warning systems
More effective evacuation procedures
Stronger buildings and infrastructure
Greater financial resources for recovery
Lower death tolls but often higher economic costs

🏢 LICs (e.g., parts of Indonesia, Philippines)

Limited monitoring capabilities
Densely populated areas near volcanoes
Less resilient infrastructure
Fewer resources for evacuation and recovery
Often higher death tolls but sometimes lower economic costs

The Benefits of Volcanoes

Despite their destructive potential, volcanoes also provide significant benefits:

Fertile soil: Volcanic ash weathers to create some of the most fertile soils on Earth.
Geothermal energy: Countries like Iceland harness volcanic heat for renewable energy.
Tourism: Volcanic landscapes attract tourists, boosting local economies.
Building materials: Volcanic rock is used in construction.
Mineral deposits: Many valuable minerals are associated with volcanic activity.

This explains why people continue to live near volcanoes despite the risks they pose. The challenge is finding ways to enjoy these benefits while minimising the hazards through effective monitoring, planning and response strategies.

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