Plate Tectonics » Volcanoes - formation, types, and impacts

What you'll learn this session

Study time: 30 minutes

The formation process of volcanoes and how they relate to plate boundaries
Different types of volcanoes and their characteristics
The primary and secondary impacts of volcanic eruptions
Case studies of significant volcanic eruptions
How humans adapt to and manage volcanic hazards

Introduction to Volcanoes

Volcanoes are one of the most dramatic features of our planet's landscape. They form when magma from the Earth's mantle rises to the surface and erupts as lava. These fascinating but potentially devastating natural features are closely linked to plate tectonics and occur primarily at plate boundaries.

Key Definitions:

Volcano: An opening in the Earth's crust through which molten rock, ash and gases erupt.
Magma: Molten rock beneath the Earth's surface.
Lava: Magma that has reached the Earth's surface.
Crater: A bowl-shaped depression at the top of a volcano.
Vent: The opening through which volcanic materials are erupted.

Volcano Formation

Volcanoes form when magma finds its way to the Earth's surface. This typically happens at plate boundaries where tectonic activity creates pathways for magma to rise. The three main plate boundaries where volcanoes form are:

🌋 Destructive (Convergent) Boundaries

When an oceanic plate subducts beneath a continental plate, the descending plate melts in the mantle, creating magma that rises to form volcanoes. Examples include the volcanoes of the Pacific Ring of Fire.

🌋 Constructive (Divergent) Boundaries

As plates move apart, pressure is released, allowing magma to rise and form volcanoes. This occurs at mid-ocean ridges like the Mid-Atlantic Ridge, creating new seafloor.

🌋 Hot Spots

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

Types of Volcanoes

Volcanoes come in different shapes and sizes, determined by the type of eruption and the materials erupted. The three main types are:

⛰ Shield Volcanoes

Characteristics: Broad, gently sloping sides formed from fluid lava flows.

Eruptions: Generally non-explosive with runny basaltic lava.

Example: Mauna Loa in Hawaii is the world's largest active shield volcano.

⛰ Composite Volcanoes

Characteristics: Steep-sided, symmetrical cones built up of alternating layers of lava, ash and rock fragments.

Eruptions: Often explosive with viscous lava.

Example: Mount Fuji in Japan and Mount St. Helens in the USA.

⛰ Cinder Cones

Characteristics: Simple, small, steep-sided cones built from ejected lava fragments.

Eruptions: Moderately explosive, ejecting cinders and ash.

Example: Paricutin in Mexico, which famously grew in a farmer's field in 1943.

Volcanic Eruptions and Their Impacts

Volcanic eruptions can have significant impacts on people, the environment and the economy. These impacts can be both positive and negative and can be felt both immediately and over a longer period.

⚠ Primary Impacts

Lava flows: Destroy buildings and infrastructure, but move slowly enough for evacuation.
Pyroclastic flows: Fast-moving clouds of hot gas and volcanic matter that can travel at speeds of up to 700 km/h, causing immediate destruction.
Ash falls: Can collapse roofs, damage crops, contaminate water supplies and cause respiratory problems.
Lahars: Volcanic mudflows that can bury entire settlements.
Toxic gases: Including sulphur dioxide and carbon dioxide, which can cause health problems and even death.

⚠ Secondary Impacts

Climate change: Large eruptions can release ash and gases that block sunlight, cooling the Earth's surface.
Economic disruption: Damage to infrastructure, agriculture and tourism.
Displacement: People may need to relocate temporarily or permanently.
Disease: Contaminated water supplies and poor living conditions in evacuation centres can lead to disease outbreaks.
Psychological impacts: Trauma and stress from experiencing a disaster.

Case Study: Mount Pinatubo, Philippines (1991)

The eruption of Mount Pinatubo on 15 June 1991 was one of the largest volcanic eruptions of the 20th century.

Primary impacts:

Over 800 people killed, mostly from building collapses due to ash accumulation
Pyroclastic flows extended up to 16 km from the volcano
Ash fall covered an area of over 7,500 km²

Secondary impacts:

Global temperatures dropped by about 0.5°C for two years due to sulphur dioxide emissions
Over 200,000 people became homeless
Agricultural land was devastated, affecting livelihoods
The nearby US Clark Air Base was permanently closed

Management: Successful monitoring and early evacuation saved thousands of lives. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the US Geological Survey (USGS) detected signs of an imminent eruption months in advance.

Positive Impacts of Volcanoes

While volcanic eruptions can be destructive, they also bring benefits:

Fertile soils: Volcanic ash and lava break down to form some of the most fertile soils on Earth, supporting productive agriculture.
Geothermal energy: Heat from volcanic systems can be harnessed as a renewable energy source.
Tourism: Volcanic landscapes attract visitors, boosting local economies.
Building materials: Volcanic rocks and minerals are used in construction.
Creation of new land: Lava flows can extend coastlines and create new islands.

Living with Volcanoes: Monitoring and Management

People continue to live near volcanoes despite the risks, often because of the fertile soil, natural resources, or cultural attachment to the area. To reduce the risks, various monitoring and management strategies are employed:

🔍 Monitoring Techniques

Seismometers: Detect earthquake activity that often precedes eruptions.
Gas monitoring: Measures changes in gas emissions that might indicate rising magma.
Ground deformation: GPS and satellite data track bulging or swelling of the volcano.
Thermal imaging: Detects heat changes that might signal magma movement.
Historical analysis: Studying past eruption patterns to predict future behaviour.

🛠 Management Strategies

Hazard mapping: Identifying areas at risk from different volcanic hazards.
Early warning systems: Alerting populations to potential eruptions.
Evacuation plans: Establishing routes and procedures for quick evacuation.
Land use planning: Restricting development in high-risk areas.
Engineering solutions: Building barriers to divert lava flows or reinforcing buildings against ash fall.
Education: Teaching communities about volcanic hazards and how to respond.

Case Study: Eyjafjallajökull, Iceland (2010)

The eruption of Eyjafjallajökull in April 2010 was relatively small but had massive global impacts due to the ash cloud it produced.

Impacts:

Over 100,000 flights cancelled across Europe
Economic losses estimated at £1.1 billion for the airline industry
10 million passengers stranded worldwide
Disruption to global supply chains and business

Lessons learned: The eruption highlighted how interconnected our modern world is and how vulnerable global systems can be to natural events. It led to improved protocols for dealing with volcanic ash in aviation and better international coordination.

Summary

Volcanoes are fascinating geological features that form primarily at plate boundaries when magma rises to the Earth's surface. They come in different types shield, composite and cinder cone each with distinctive characteristics and eruption styles. While volcanic eruptions can cause significant destruction through lava flows, pyroclastic flows, ash falls and other hazards, they also bring benefits such as fertile soil and geothermal energy.

Living with volcanoes requires effective monitoring and management strategies to reduce risks to people and property. By understanding how volcanoes form, the types of eruptions they produce and their potential impacts, communities can better prepare for and respond to volcanic hazards.