🌋Volcanology Unit 9 – Volcano Monitoring Techniques

Key Concepts and Terminology

• Volcanic monitoring involves the systematic observation and measurement of volcanic activity to assess hazards and predict eruptions
• Precursors are signals or changes in volcanic activity that may indicate an impending eruption (seismicity, gas emissions, ground deformation)
• Seismicity refers to the frequency, intensity, and location of earthquakes associated with volcanic activity
  • Volcano-tectonic (VT) earthquakes result from rock fracturing due to magma movement or tectonic stresses
  • Long-period (LP) earthquakes are caused by fluid movement within the volcanic system
  • Harmonic tremors are continuous, rhythmic seismic signals often associated with magma ascent
• Gas emissions, particularly sulfur dioxide (SO2), carbon dioxide (CO2), and hydrogen sulfide (H2S), can provide insights into magma degassing and potential eruptions
• Ground deformation occurs when magma intrusion or pressure changes cause the Earth's surface to inflate or deflate
• Hydrothermal activity involves the interaction between magma, water, and rock, leading to the formation of hot springs, geysers, and fumaroles
• Lahars are destructive volcanic mudflows that can travel long distances and pose significant hazards to downstream communities

Geological Background

• Understanding the geological setting and history of a volcano is crucial for effective monitoring and hazard assessment
• Tectonic setting influences the type and behavior of volcanoes (subduction zones, rift zones, hot spots)
• Magma composition (basaltic, andesitic, rhyolitic) affects the style and explosivity of eruptions
  • Basaltic magmas are less viscous and often result in effusive eruptions (lava flows)
  • Rhyolitic magmas are more viscous and can lead to explosive eruptions (pyroclastic flows, ash plumes)
• Eruptive history provides insights into the frequency, magnitude, and types of past eruptions
• Stratigraphy and deposits from previous eruptions can help reconstruct the volcano's behavior and assess potential hazards
• Structural features, such as calderas, domes, and fissures, can influence the path and style of magma ascent
• Hydrothermal systems and alteration can affect the stability of volcanic edifices and contribute to phreatic eruptions

Types of Volcanic Monitoring

• Seismic monitoring uses seismometers to detect and locate earthquakes associated with magma movement and rock fracturing
• Deformation monitoring tracks changes in the shape of the volcanic edifice using GPS, tiltmeters, and InSAR
• Gas monitoring measures the composition and flux of volcanic gases to assess magma degassing and potential eruptions
  • Direct sampling, UV spectrometers, and satellite remote sensing are used to monitor gas emissions
• Hydrothermal monitoring involves tracking changes in water chemistry, temperature, and flow rates of hot springs and fumaroles
• Visual monitoring uses cameras and field observations to detect changes in volcanic activity (ash plumes, lava flows, dome growth)
• Infrasound monitoring detects low-frequency sound waves generated by volcanic explosions and gas emissions
• Thermal monitoring uses infrared cameras and satellite imagery to measure heat flux and detect thermal anomalies
• Gravity and magnetic monitoring can detect changes in subsurface magma storage and movement

Ground-Based Monitoring Techniques

• Seismic networks consist of strategically placed seismometers that continuously record ground motion
  • Broadband seismometers cover a wide range of frequencies and are used to characterize different types of seismic events
  • Short-period seismometers are more sensitive to high-frequency events and are useful for detecting local earthquakes
• GPS (Global Positioning System) stations measure ground deformation by tracking changes in the position of fixed points on the Earth's surface
• Tiltmeters are sensitive instruments that measure small changes in the tilt of the ground, indicative of subsurface magma movement
• Electronic distance measurement (EDM) uses laser ranging to precisely measure distances between benchmarks and detect ground deformation
• Gas sampling and analysis can be done using Fourier-transform infrared (FTIR) spectrometers, gas chromatographs, and electrochemical sensors
• Acoustic flow monitors (AFMs) measure the sound waves generated by volcanic explosions and gas emissions to estimate the velocity and volume of ejecta
• Borehole strainmeters are installed in deep wells to measure small changes in rock strain caused by magma intrusion or pressure changes
• Muon tomography uses cosmic-ray muons to image the internal structure of volcanoes and detect magma movement

Remote Sensing Methods

• Satellite remote sensing provides a synoptic view of volcanic activity and can monitor volcanoes in remote or inaccessible areas
• Synthetic Aperture Radar (SAR) uses microwave radiation to create detailed images of the Earth's surface and measure ground deformation
  • Interferometric SAR (InSAR) compares two or more SAR images to detect small changes in ground elevation
• Thermal infrared (TIR) sensors, such as MODIS and ASTER, can detect thermal anomalies and measure surface temperatures associated with volcanic activity
• Ultraviolet (UV) sensors, like OMI and TROPOMI, can measure sulfur dioxide (SO2) emissions from volcanoes, which are indicative of magma degassing
• Light Detection and Ranging (LiDAR) uses laser pulses to create high-resolution digital elevation models (DEMs) and detect changes in volcanic topography
• Hyperspectral imaging, such as with the Hyperion sensor, can identify and map volcanic minerals and alteration zones
• Gravimetric satellites, like GRACE, can measure changes in the Earth's gravity field caused by magma movement and mass redistribution
• Infrasound arrays can detect low-frequency sound waves generated by volcanic explosions and gas emissions from great distances

Data Analysis and Interpretation

• Seismic data analysis involves identifying and classifying different types of seismic events (volcano-tectonic, long-period, harmonic tremor)
  • Spectral analysis can help distinguish between different seismic sources and magma transport processes
  • Seismic tomography uses the travel times of seismic waves to image the internal structure of volcanoes and detect magma storage zones
• Deformation data analysis aims to quantify and model ground surface changes to infer subsurface magma movement and pressure changes
  • Mogi and Okada models are commonly used to estimate the location, depth, and volume of magma intrusions
• Gas data analysis focuses on calculating gas emission rates, ratios, and temporal variations to assess magma degassing and eruption potential
  • Correlation between gas emissions and seismic or deformation data can provide a more comprehensive understanding of volcanic processes
• Multidisciplinary data integration combines different monitoring techniques to develop a holistic view of volcanic activity and improve eruption forecasting
• Machine learning and statistical methods, such as pattern recognition and time series analysis, can help identify precursory signals and forecast eruptions
• Numerical modeling, including fluid dynamics and rock mechanics simulations, can help interpret monitoring data and understand magma transport processes

Hazard Assessment and Risk Management

• Hazard assessment involves identifying and characterizing the potential volcanic hazards (lava flows, pyroclastic density currents, ash fall, lahars)
  • Hazard maps delineate areas that could be affected by different volcanic hazards based on historical eruptions, geological mapping, and numerical simulations
• Risk assessment considers the likelihood and consequences of volcanic hazards on people, infrastructure, and the environment
  • Vulnerability and exposure analysis help quantify the potential impacts of volcanic eruptions on society
• Early warning systems integrate real-time monitoring data, hazard assessment, and communication protocols to provide timely alerts and evacuation orders
• Hazard communication and public outreach are essential for raising awareness, promoting preparedness, and facilitating effective emergency response
  • Collaboration between volcanologists, emergency managers, and local communities is crucial for successful risk reduction
• Long-term land-use planning and zoning regulations can help mitigate volcanic risks by discouraging development in high-hazard areas
• Contingency planning and crisis management involve developing strategies and resources to respond to and recover from volcanic emergencies
• Post-eruption monitoring and assessment are important for understanding the impacts of eruptions and guiding rehabilitation and reconstruction efforts

Real-World Case Studies

• Mount St. Helens (USA, 1980): Demonstrated the importance of seismic monitoring and deformation studies in predicting and mitigating the impacts of explosive eruptions
  • Seismic precursors and bulging of the volcano's north flank were key indicators of the impending eruption
• Pinatubo (Philippines, 1991): Showcased the successful use of satellite remote sensing and ground-based monitoring to forecast and manage a large-scale volcanic crisis
  • Timely evacuation of tens of thousands of people based on monitoring data and hazard assessments saved countless lives
• Eyjafjallajökull (Iceland, 2010): Highlighted the global impacts of volcanic ash on aviation and the importance of ash dispersion modeling and risk assessment
  • Disruption of European air traffic for several weeks due to the presence of volcanic ash in the atmosphere
• Soufrière Hills (Montserrat, 1995-present): Illustrates the challenges of long-term volcanic risk management and the socioeconomic consequences of prolonged eruptive activity
  • Gradual evacuation and relocation of the island's population due to the ongoing volcanic hazards
• Kilauea (Hawaii, 2018): Demonstrated the use of multiple monitoring techniques, including seismicity, deformation, and gas emissions, to track the evolution of a large-scale effusive eruption
  • Lava flows and associated hazards (laze, volcanic smog) impacted residential areas and infrastructure
• Nevado del Ruiz (Colombia, 1985): Emphasized the tragic consequences of inadequate hazard communication and lack of preparedness in the face of volcanic risks
  • Lahars triggered by the eruption killed more than 23,000 people in the town of Armero
• Taal (Philippines, 2020): Showcased the rapid response and evacuation efforts based on real-time monitoring data and hazard assessments during a sudden-onset volcanic crisis
  • Phreatic explosion and subsequent magmatic eruption led to the evacuation of hundreds of thousands of people from the surrounding areas