🌋Volcanology Unit 8 – Volcanic Hazards and Risk Assessment

Key Volcanic Concepts

• Magma composition influences eruption style and hazards (basaltic, andesitic, rhyolitic)
• Volcanic gases contribute to explosive eruptions and pose health risks (sulfur dioxide, carbon dioxide, hydrogen sulfide)
  • Sulfur dioxide can cause acid rain and respiratory issues
  • Carbon dioxide can accumulate in low-lying areas, leading to asphyxiation
• Pyroclastic density currents are high-speed, ground-hugging flows of hot ash, pumice, and gas
• Lahars are destructive mudflows or debris flows triggered by volcanic activity
  • Can be generated by melting snow and ice, heavy rainfall, or crater lake breakout
• Lava flows vary in speed and destructive potential based on composition and viscosity (pahoehoe, aa, blocky)
• Tephra includes ash, pumice, and other volcanic ejecta that can cause respiratory issues, infrastructure damage, and aviation hazards
• Volcanic edifice instability can lead to catastrophic sector collapses and debris avalanches

Types of Volcanoes and Eruptions

• Shield volcanoes have gentle slopes and are formed by effusive eruptions of low-viscosity lava (Mauna Loa, Kilauea)
• Stratovolcanoes have steep slopes and are built by alternating layers of lava, ash, and pyroclastic material (Mount Fuji, Mount St. Helens)
  • Often associated with explosive eruptions and a wide range of hazards
• Cinder cones are small, steep-sided volcanoes built from ejected lava fragments (Parícutin, Mexico)
• Lava domes are formed by viscous lava piling up around the vent (Soufrière Hills, Montserrat)
  • Can collapse and generate pyroclastic density currents
• Phreatic eruptions occur when magma heats groundwater, causing steam-driven explosions (Ontake, Japan)
• Plinian eruptions are large, explosive events characterized by high ash columns and widespread tephra fallout (Vesuvius, 79 AD)
• Effusive eruptions involve the quiet outpouring of lava with minimal explosive activity (Kilauea, Hawaii)

Volcanic Hazards and Their Effects

• Pyroclastic density currents can travel at speeds over 100 km/h, causing destruction and fatalities (Pompeii, 79 AD)
• Lahars can travel long distances, destroying infrastructure and burying communities (Nevado del Ruiz, 1985)
  • Can occur during or long after an eruption, making them a persistent hazard
• Lava flows can ignite fires, destroy structures, and disrupt transportation routes (Eldfell, Heimaey, 1973)
• Tephra fallout can collapse roofs, disrupt utilities, and cause respiratory issues (Mount Pinatubo, 1991)
  • Can also impact agriculture and livestock
• Volcanic gases can cause acid rain, air pollution, and pose health risks (Kilauea, ongoing)
• Sector collapses and debris avalanches can reshape landscapes and trigger tsunamis (Mount St. Helens, 1980)
• Secondary hazards include flooding, wildfires, and infrastructure damage

Monitoring and Prediction Methods

• Seismic monitoring detects earthquakes and volcanic tremor, indicating magma movement (seismometers, seismic arrays)
• Ground deformation measurements track changes in the volcano's shape due to magma intrusion (GPS, tiltmeters, InSAR)
  • Inflation often precedes eruptions, while deflation occurs during or after
• Gas monitoring assesses changes in the composition and emission rates of volcanic gases (COSPEC, DOAS, MultiGAS)
• Thermal monitoring identifies heat signatures associated with magma ascent and surface activity (infrared cameras, satellite imagery)
• Hydrological monitoring tracks changes in water chemistry, temperature, and level in nearby springs, streams, and lakes
• Acoustic monitoring detects low-frequency sounds generated by magma movement and gas release (infrasound sensors)
• Integrated monitoring systems combine multiple data streams for improved eruption forecasting and early warning

Risk Assessment Techniques

• Hazard identification involves recognizing potential hazards based on the volcano's history, characteristics, and current activity
• Vulnerability assessment evaluates the exposure and susceptibility of people, infrastructure, and ecosystems to volcanic hazards
  • Considers factors such as population density, land use, and socioeconomic conditions
• Risk analysis combines hazard and vulnerability data to estimate the likelihood and consequences of volcanic events
• Probabilistic risk assessment uses statistical methods to quantify uncertainty and generate risk estimates (event trees, Bayesian belief networks)
• Multi-hazard risk assessment considers the interactions and cascading effects of multiple hazards (lahars, tephra fallout, and flooding)
• Risk perception studies investigate how individuals and communities understand and respond to volcanic risk
• Cost-benefit analysis weighs the costs of mitigation measures against the potential losses from volcanic events

Hazard Mapping and Zoning

• Hazard maps delineate areas potentially affected by specific volcanic hazards (lava flows, pyroclastic density currents, tephra fallout)
  • Based on historical events, geological evidence, and numerical simulations
• Hazard zonation divides the area around a volcano into zones of varying hazard levels (high, medium, low)
  • Used to guide land-use planning, evacuation routes, and emergency response
• Probabilistic hazard maps display the likelihood of a given area being affected by a specific hazard over a certain time period
• Temporal hazard maps show how hazard zones change over time based on the volcano's activity level and monitoring data
• Hazard maps are communicated to stakeholders and the public through various media (print, digital, interactive)
• Regular updates to hazard maps incorporate new data, improved modeling techniques, and changes in the volcano's behavior
• Integration of hazard maps with vulnerability and exposure data supports risk-informed decision-making

Mitigation Strategies and Emergency Planning

• Land-use planning restricts development in high-hazard zones and promotes sustainable land management practices
• Building codes and engineering solutions improve the resilience of structures to volcanic hazards (reinforced roofs, lahar barriers)
• Evacuation planning identifies safe zones, routes, and shelters, and establishes protocols for timely and orderly evacuation
  • Considers the needs of vulnerable populations (elderly, disabled, low-income)
• Early warning systems disseminate timely and actionable information to authorities, emergency responders, and the public
  • Utilize multiple communication channels (sirens, text alerts, social media)
• Education and outreach programs raise awareness of volcanic hazards and promote preparedness and self-protective actions
• Simulation exercises and drills test and improve the effectiveness of emergency plans and response capabilities
• Post-eruption recovery planning addresses the short- and long-term needs of affected communities (temporary housing, infrastructure repair, economic recovery)

Case Studies and Real-World Applications

• Mount Pinatubo, Philippines (1991): Successful evacuation of tens of thousands of people based on timely warnings and hazard zonation
• Eyjafjallajökull, Iceland (2010): Disruption of European air travel due to tephra fallout, highlighting the global impact of volcanic eruptions
  • Led to improvements in volcanic ash forecasting and aviation safety protocols
• Nevado del Ruiz, Colombia (1985): Tragic lahar disaster that killed over 23,000 people, emphasizing the importance of hazard communication and preparedness
• Mount Merapi, Indonesia (2010): Effective use of hazard maps and community-based evacuation planning during a major eruption
  • Demonstrated the value of integrating scientific knowledge with local wisdom and social networks
• Long Valley Caldera, California, USA (ongoing): Comprehensive monitoring and hazard assessment of a restless caldera in a highly populated area
• Soufrière Hills, Montserrat (1995-present): Long-term eruption that has reshaped the island's geography, economy, and society
  • Illustrates the challenges of living with an active volcano and the importance of adaptive risk management strategies