Volcanoes

Distribution of Volcanic Hazards

• Most active volcanoes occur at or near plate boundaries

• Many (about 75%) occur around the 'Ring of Fire' surrounding the Pacific Ocean

• Vulcanicity (volcanic activity) is focused on constructive and destructive plate margins

  • At constructive margins, eruptions tend to be small and >effusive 

  • The eruptions are usually basaltic lava:

    • Low gas content

    • Low viscosity

    • Higher temperature

  • At destructive margins, eruptions tend to be explosive as the magma is forcing its way to the surface

  • These eruptions are often andesitic

    • High gas content

    • High viscosity

    • Lower temperature

• Volcanoes can also be found at hot spots in the middle of plates, like Hawaii in the central Pacific

Examiner Tips and Tricks

It is important that you are confident to describe distribution.

• What is the general pattern?

• Does the pattern relate to anything else for example the location of plate boundaries?

• Are they near the equator or further away?

• Are they inland or coastal?

• Use map features to help with your description - place names, compass rose, latitude and longitude

Magnitude of Volcanic Hazards

• Some volcanic eruptions are gentle and effusive while others are hugely explosive

  • This is dependent on the magma composition

• The Volcanic Explosivity Index (VEI) is used to measure the magnitude of an eruption

• This is a logarithmic scale from 0-8 

• is calculated based on a series of measurements and observations

  • These include:

    • Height of material ejected into the atmosphere

    • Volume of material

    • Duration of the eruption

Primary Hazards

• Although they are all unique, volcanic eruptions have common hazards

• Primary (a direct result of the eruption)

  • pyroclastic flows

  • landslides

  • ash fall out

  • earthquakes

Diagram to show volcanic hazards

• Tephra – solid material of varying sizes that is ejected by a volcano – ranges from ash (less than 2mm in diameter) to volcanic bombs (more than 64mm)

• Ash fallout – large quantities of ash carried by the wind and deposited on the ground It can travel many km, causing respiratory problems, injuries, damage, deaths and disruption to air transport.

  • E.g. the 2010 Eyjafjallajökull eruption in Iceland produced an ash cloud that disrupted air travel in Europe for several weeks

• Pyroclastic flow- a super-heated mixture of gas and tephra that flows at speeds of up to 700 km per hour

  • This is one of the deadliest volcanic hazards as they can travel long distances and destroy everything in their path

  • E.g. when Fuego volcano erupted in Guatemala in 2018, pyroclastic flows destroyed several nearby towns

• Lava flow – lava flows travel at different speeds depending on slope, temperature and viscosity

  • Most move slowly enough that they are not a risk to human life but can cause significant damage to property and infrastructure

  • The fastest flows can reach speeds of up to 60 mph

  • In the 2021 eruption of Mount Nyiragongo in the Democratic Republic of Congo, lava flows travelled almost 10km destroying properties and killing over 30 people

• Volcanic gases – eruptions can release large quantities of gases such as sulphur dioxide and carbon dioxide

  • They are hazardous to human health causing respiratory problems and deaths

  • E.g. Kilauea in Hawaii (USA) releases large amounts of sulphur dioxide leading to air quality alerts and health warnings for residents

Secondary Hazards

• Lahars – mudflows that occur when tephra or ash mixes with water, either from rainfall, or from melted snow and ice

  • They are fast flowing and destroy everything in their path

  • E.g. the lahars that occurred when Mount Pinatubo erupted in the Philippines in 1991 caused extensive damage and disruption

• Jökulhlaups - floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption

  • The 2010 eruption of Eyjafjallajökull triggered a jökulhlaup which destroyed several bridges and roads

• Acid rain – forms when sulphur dioxide gas emitted during the eruption reacts with water vapour in the atmosphere to form sulphuric acid

• It can damage crops, forests, infrastructure like limestone buildings and aquatic ecosystems

Map to show extent of lahars in eruption of Mount Pinatubo

Frequency & Regularity of Hazards

• Volcanic eruptions occur with varying frequency and regularity depending on the type of volcano and its location

  • Shield volcanoes tend to be found at constructive plate margins and are typified by high frequency, low magnitude eruptions

  • Stratovolcanoes tend to be found at destructive plate margins and are typified by low frequency, high magnitude eruptions

Diagram of a shield volcano

• Some volcanoes erupt more frequently and regularly than others

  • Mount Stromboli in Italy usually erupts every 20-40 minutes

  • Mount Pinatubo in the Philippines had not erupted for around 500 years before its eruption in 1991

• Scientists study the geological history of volcanoes (e.g. eruptions and gas emissions) to try to predict when the next eruption might occur

• Volcanic eruptions can occur with few warning signs and do not necessarily follow historical patterns

• making them difficult to predict

Predicting Volcanic Events

• There are warning signs before most volcanic eruptions

• Volcanologists monitor changes using GPS, tilt meters, satellites, seismometers and gas detection

• Signs of an eruption include:

  • Magma rising which can be detected by heat sensors and satellites

  • Ground deformation as rising magma causes bulges

  • Increased emissions of sulphur dioxide and other gases

  • Increased seismic activity caused by magma movement detected by seismometers

Methods of monitoring volcanoes

Examiner Tips and Tricks

It is important to be aware that while there are several methods used to monitor and predict volcanic eruptions, it is impossible to be certain about exactly when a volcano will erupt and with what magnitude. Indeed, there are many examples where even heavily monitored volcanoes have taken people by surprise.

• For example, Mount Ontake in Japan erupted suddenly and unexpectedly in 2014 killing 63 people. It hadn’t shown any signs of an eruption or increased activity so no warnings or alerts were issued. Hikers and tourists on the mountain were taken by surprise and many were killed or injured.

Primary & Secondary Impacts of Eruptions

• Primary impacts are the immediate effects of the hazard such as injuries and deaths, and damage to property and infrastructure

• Secondary impacts are the longer-term effects of the hazard such as economic losses, social and psychological consequences

Examples of Impacts of Volcanic Hazards SEEP FACTORS

long-Term and short-term Responses to Volcanic Hazards

• Long-term these are immediate measures taken to reduce the impacts of future eruptions

• Short-term responses usually happen immediately before, during or after a volcanic eruption

Examples of Long and Short-term Responses

Responses can also be categorised as prevention, preparedness, mitigation and adaptation

Comparison Table of Volcano Types

Structural and Design Mitigation for Buildings

To prevent significant damage from volcanic hazards, buildings can be engineered with specific design features:

Steeply Pitched Roofs:

• Designing roofs with a greater slope ensures that volcanic ash (tephra) slides off easily.

• This prevents roof collapse from the immense weight of accumulated ash, which becomes even heavier if it rains.

Reinforced Roof Strength:

• Using materials like reinforced concrete or heavy-duty steel to increase the load-bearing capacity of the roof against static ash loads and the dynamic impact of falling volcanic bombs.

Smooth Surface Materials:

• Utilizing corrugated iron or smooth tiles to reduce friction, allowing tephra to shed more efficiently.

Sealing and Filtration Systems:

• Installing specialized seals on windows and doors to prevent the infiltration of fine ash particles and toxic gases (SO2, CO2), which can cause respiratory failure and damage electrical systems.

Simplified Building Footprints:

• Minimizing roof "valleys" and complex joints where ash can naturally collect and create structural pressure points.

Strengthened Foundations:

• Building robust foundations to withstand the seismic tremors and ground shaking that typically accompany rising magma.

Protective Deflection Barriers:

• In specific locations, reinforced masonry walls or channels can be built to divert lahars or slow-moving lava flows away from residential structures.

Non-Flammable Materials:

• Using fire-resistant roofing and siding to protect buildings from incendiary damage caused by hot tephra or proximity to lava.