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The Global Positioning System (GPS) has revolutionized the way scientists monitor volcanic activity and study lava flows around the world. This sophisticated satellite-based technology provides unprecedented precision in measuring ground movements, enabling volcanologists to better understand volcanic behavior, predict potential eruptions, and protect communities living near active volcanoes. When magma accumulates or migrates beneath a volcano, it can cause pressurization and related ground deformation, and characterization of surface deformation provides important constraints on the potential for future volcanic activity, especially in combination with seismic activity, gas emissions, and other indicators.
Understanding Volcanic Ground Deformation
Ground deformation measurements provide an important indicator about what is happening beneath a volcano, as magma accumulates in an underground reservoir before an eruption, the ground surface typically swells (named inflation). This inflation process occurs when magma enters the volcanic system or releases gas, causing pressurization. If magma enters the system or releases gas, it becomes pressurized, and the ground above becomes inflated like a balloon, moving upward and outward; similarly, if magma leaves the system or fluid pressures decrease, the volcano “deflates” and moves downward and inward.
Ground surface deformation is recognised as a reliable indicator of an impending eruption and can give clues to magmatic processes at depth. By carefully monitoring these subtle changes in the Earth’s surface, scientists can gain valuable insights into what is occurring deep within the volcanic plumbing system, potentially providing critical early warning signs of an impending eruption.
How GPS Technology Works for Volcano Monitoring
The Basics of GPS Volcano Monitoring
To use GPS data for volcano monitoring, multiple receivers are placed around a volcano as a GPS network, and in some locations, instruments are permanently installed and record data continuously. These specialized GPS systems differ significantly from the consumer-grade devices found in smartphones and vehicle navigation systems.
While relatively inexpensive GPS receivers, like those in vehicle navigation systems, smart phones, and handheld units, can determine their position on the Earth’s surface to within a few meters, with more sophisticated receivers and data-analysis techniques, receiver positions can be determined to less than a centimeter (fraction of an inch), which is very important when applied as a volcano monitoring technique. This level of precision is essential because scientists using GPS for volcano monitoring need to be able to measure changes that are less than a half of an inch (about a centimeter) to detect signs of magma moving underground.
Continuous vs. Survey-Mode GPS
GPS is utilized in one of two modes: continuous and survey. Continuous GPS systems use permanently installed receivers and antennas at fixed locations to track the motion of specific stations over time. These stations operate 24 hours a day, 7 days a week, providing an uninterrupted stream of data that scientists can analyze for any signs of volcanic unrest.
Survey-mode GPS, on the other hand, involves periodic measurements at established benchmarks. Scientists visit these locations at regular intervals—often annually or during specific volcanic events—to collect data for comparison over time. In Hawai’i Volcanoes National Park, over 50 continuous GPS stations are supplemented by over 100 sites that are occupied for a few days each during annual or event-driven GPS campaigns, and this combination of methods provides the best possible temporal and spatial resolution of deformation patterns associated with active volcanism.
Network Configuration and Data Analysis
By looking at data from a single receiver over a period of time, scientists can determine whether the ground surface has moved (deformed), and by combining the data collected from a GPS network, it is possible to get a larger view of which areas of the volcano’s surface are moving as well as the speed and direction of movement; this large-scale picture of volcano deformation can be used to construct a model of what is happening beneath the surface—for example, the location of any magma reservoirs or active faults.
GPS can precisely measure both horizontal and vertical motions, and GPS and other instruments used to measure deformation may detect motion at a volcano before any earthquakes occur, and these changes in shape may accelerate immediately before an eruption, making GPS a valuable monitoring tool. This capability to detect pre-seismic deformation is particularly valuable, as it can provide additional warning time before volcanic activity intensifies.
Monitoring Ground Deformation at Active Volcanoes
Detecting Magma Movement
GPS stations installed around volcanoes continuously track ground deformation over time, providing scientists with critical data about subsurface magma movement. Changes in the position of these stations can indicate magma accumulation or migration beneath the surface, which may signal an impending eruption. GPS measurements can be used to estimate the location and amount of magma accumulating beneath the surface; for example, Mauna Loa Volcano has experienced multiple episodes of inflation since its 1984 eruption, and it has been well documented since the mid-1990’s, and these data have helped HVO scientists to better understand magma movement and storage beneath the volcano.
Today’s GPS networks record data in real time and detect rapid changes associated with magma moving towards the surface in the hours to days before an eruption. This real-time capability represents a significant advancement in volcano monitoring, allowing scientists to respond quickly to changing conditions and issue timely warnings to at-risk populations.
Case Studies: GPS Success Stories
The effectiveness of GPS monitoring has been demonstrated at numerous volcanoes worldwide. A 2015 study created a tool that tracks the contraction and expansion of volcanoes with real-time surface deformation data and is able to monitor the dynamics of magma movement in seconds; the team of researchers applied their tool to the 2008 Mount Etna eruption in Sicily, Italy as an example, and using GPS data from ten stations, the scientists simulated a real-time situation and monitored changes in the magma system for over a year prior to the eruption; this modeling displayed rising magma and a dike intrusion within Mount Etna, as well as the movement of magma towards the surface of the volcano the night before the eruption.
At Kīlauea volcano in Hawaii, GPS monitoring has revealed fascinating insights into volcanic processes. The rate of incoming magma supply beneath a volcano is a key factor to forecasting its eruptive activity, and a 2012 study used GPS data, in addition to InSAR and gas chemistry, to estimate the rate of the magma supply in the Kīlauea volcano in Hawai’i from 2003-2007; the researchers determined that the rate more than doubled over that time period. This information proved crucial for understanding the volcano’s subsequent eruptive behavior.
It has long been known that the south flank of Kīlauea is moving seaward at a rate of several centimeters (a few inches) per year; this motion is continuous, but GPS monitoring has also detected discrete episodes of accelerated motion about every 2 years, known as a slow earthquake, the motion takes place over 2-3 days and would be equivalent to a ~M5.5 earthquake if it were to occur all at once.
Inflation and Deflation Cycles
One of the most important phenomena that GPS monitoring reveals is the inflation and deflation cycles of volcanoes. During inflation, points on the volcano’s surface move upward and outward as magma accumulates in subsurface reservoirs. During deflation, these same points move downward and inward as magma drains away or erupts at the surface. By tracking these movements with millimeter-scale precision, scientists can infer the location, size, and behavior of magma chambers deep beneath the volcano.
These deformation patterns provide critical information for eruption forecasting. Precursory ground deformation can be used to forecast the place and, with luck, the size of an eruption. The ability to detect and interpret these subtle changes has significantly improved volcanic hazard assessment and emergency response planning worldwide.
Tracking and Mapping Lava Flows
Beyond monitoring ground deformation, GPS technology plays a vital role in mapping the extent and movement of lava flows during volcanic eruptions. Volcanologists routinely use hand-held GPS receivers to map lava flows and other volcanic features, and they can now use specialized GPS receivers and sophisticated analysis software to continuously track the subtle ground movements that precede an eruption.
During active eruptions, scientists use GPS equipment to accurately map the boundaries of advancing lava flows, documenting their extent, speed, and direction. This information is critical for hazard assessment and response planning, helping emergency managers determine which areas are at risk and when evacuations may be necessary. The precise spatial data collected through GPS mapping also contributes to long-term studies of volcanic behavior and helps improve models of lava flow dynamics.
GPS mapping of lava flows provides valuable data for understanding eruption rates and volumes. By repeatedly surveying the same areas over time, scientists can calculate how much lava has been erupted and how quickly it is being produced. This information helps volcanologists understand the magma supply system feeding the eruption and can provide insights into how long an eruption might continue.
Integration with Other Monitoring Techniques
GPS and InSAR: Complementary Technologies
Geodetic instruments include continuously recording Global Navigation Satellite System (GNSS; of which the United States’ Global Positioning System is one example) stations, borehole tiltmeters, and interferometric synthetic aperture radar (InSAR) measurements (from satellites, occupied and unoccupied aircraft systems, and ground-based sensors). While GPS provides precise point measurements at specific locations, InSAR offers broad spatial coverage, making the two technologies highly complementary.
Because InSAR detects deformation over broad areas, it is an excellent tool for mapping both large- and small-scale changes, and on Mauna Loa, InSAR helps scientists detect subtle shifts in the deformation style of the volcano. The combination of GPS’s temporal resolution and InSAR’s spatial coverage provides a comprehensive view of volcanic deformation that neither technique could achieve alone.
Multi-Parameter Monitoring Approach
Experience has shown that no single geodetic monitoring technique is adequate to detect and track the entire range of ground-motion patterns that occur at volcanoes, primarily because of the temporal and spatial diversity of volcano deformation; similarly, the magnitude of surface deformation varies widely, and geodetic monitoring strategies should therefore include multiple techniques and instrument types to cover a wide range of spatial and temporal scales.
Effective volcano monitoring requires integrating GPS data with information from seismometers, gas sensors, thermal cameras, and other instruments. Combining GPS with seismicity, gas emissions, and changes in water chemistry around the volcano paints an even better picture of what is going on below the surface. This multi-parameter approach provides a more complete understanding of volcanic processes and improves the reliability of eruption forecasts.
GPS, tilt, and InSAR (satellite radar) are the primary methods used today to track ground movement. Each technique has its strengths and limitations, and by using them together, scientists can overcome the weaknesses of individual methods and gain a more comprehensive view of volcanic activity.
Advantages of GPS for Volcano Monitoring
High Precision and Accuracy
The primary advantage of GPS over all other deformation monitoring methods is the ability to simultaneously measure horizontal and vertical displacements within accuracies of a few millimeters. This exceptional precision allows scientists to detect even the smallest ground movements that might indicate changes in volcanic activity. The three-dimensional positioning capability of GPS is particularly valuable, as volcanic deformation often involves complex patterns of movement in multiple directions.
GPS is the ultimate tool for measuring three-dimensional displacements; therefore, it is no surprise that GPS is presently the dominant method for deformation monitoring at volcanoes. The technology’s ability to provide accurate measurements in all three spatial dimensions makes it indispensable for understanding the complex deformation patterns associated with magma movement and volcanic unrest.
Real-Time Data and Continuous Monitoring
One of the most significant advantages of modern GPS systems is their ability to provide real-time data. HVO and CVO are testing a new capability, real-time volcano monitoring, which we expect will improve our ability to forecast eruptions. Real-time GPS monitoring enables scientists to detect and respond to changes in volcanic activity as they occur, rather than waiting for periodic survey results.
GPS ground deformation measurements can be continuous, automatic, conducted in all weather conditions, and provide three-dimensional positioning results, and higher computing power also means that the complex mathematics required to process GPS baselines can be easily handled in near real time. This capability for continuous, automated monitoring is especially important for volcanoes that may show rapid changes in activity with little warning.
Remote and Autonomous Operation
Once a GPS network is installed, no human presence is needed at a potentially dangerous volcanic locale. This remote monitoring capability is crucial for maintaining surveillance of hazardous volcanoes without putting scientists and technicians at risk. GPS stations can operate autonomously for extended periods, powered by solar panels and batteries, and transmit data via radio or satellite links to monitoring centers.
Additionally there is no requirement for intervisibility of stations within a GPS network, measurements can be made in all weather, 24 h per day and over relatively long distances, and GPS is well suited to operate automatically in a remote environment powered by batteries and solar panels, with the logged data being transmitted to an office via a radio link. This operational flexibility makes GPS ideal for monitoring volcanoes in remote or challenging environments where other techniques might be impractical.
Cost-Effectiveness and Accessibility
Ground deformation monitoring is considered one of the most effective tools for investigating the behaviour of active volcanoes, and the decreasing cost of GPS hardware, together with the increased reliability of the technology, facilitates such demanding applications. While high-precision GPS equipment remains more expensive than consumer-grade devices, the costs have decreased significantly over the years, making comprehensive monitoring networks more accessible to volcano observatories worldwide.
A GPS receiver and antenna cost about $4,000, and continuous GPS sites require batteries, solar panels, and radio telemetry, at a cost of about $3,000 per site. These costs, while substantial, are reasonable compared to the potential economic and human losses that could result from an unexpected volcanic eruption. The investment in GPS monitoring infrastructure can save lives and protect property by providing early warning of volcanic unrest.
Technical Aspects of GPS Volcano Monitoring
Equipment and Installation
Establishing a GPS monitoring network on a volcano requires careful planning and specialized equipment. Scientists must select appropriate locations for GPS stations that will provide good coverage of the volcanic edifice while remaining accessible for installation and maintenance. The stations must be anchored to stable bedrock to ensure that measurements reflect actual ground deformation rather than local instability or monument movement.
Each continuous GPS station consists of several key components: a high-precision GPS antenna permanently fixed to the ground, a GPS receiver that tracks signals from satellites, a power system (typically solar panels and batteries), and a telemetry system for transmitting data to the monitoring center. The antenna must be precisely positioned and securely mounted to minimize any movement that could introduce errors into the measurements.
Data Processing and Analysis
Although the graphs of processed GPS data on HVO’s public website look like simple strings of “polka dots,” there is much more to the story; it is a complex process requiring high-precision equipment, advanced software, and powerful computing capabilities. Processing GPS data to achieve millimeter-level precision requires sophisticated algorithms that account for numerous sources of error and uncertainty.
Scientists must correct for atmospheric effects, satellite orbit errors, clock biases, and many other factors that can affect the accuracy of GPS measurements. The processing software uses signals from multiple satellites simultaneously to calculate precise three-dimensional positions. For each dot on a daily GPS graph, a full 24 hours of data is used, and there is even more complexity to generate the most precise antenna locations; for example, scientists need to correct for some of the many factors that add uncertainty or noise to the primary GPS signal which further complicates the accuracy of GPS.
Network Design Strategies
During the past few years a methodology has been developed for processing data collected by GPS networks consisting of a mixed set of single-frequency and dual-frequency receivers; the strategy is to deploy a few permanent, ‘fiducial’ GPS stations with dual-frequency, geodetic-grade receivers surrounding an ‘inner’ network of low-cost receivers. This approach allows volcano observatories to maximize coverage while managing costs effectively.
The number and distribution of GPS stations required depends on the volcano’s threat level and monitoring objectives. As a rule of thumb, volcanoes in these two threat categories will require at least 12–20 permanent seismic stations within 20 km of the main volcanic vent, including several stations very close to the vent; routine deformation surveys and continuously recording permanent Global Positioning System (GPS) stations. High-threat volcanoes require more intensive monitoring with greater station density and more frequent data collection.
Applications Beyond Traditional Deformation Monitoring
Detecting Volcanic Ash Plumes
Recent research has revealed that GPS technology can provide information beyond ground deformation measurements. A 2017 study found that GNSS signal to noise ratio (SNR) data can be used to detect ash plumes rising from Redoubt and Etna volcanoes; the researchers found that large pieces of ash affect the satellite signal reaching the GNSS station during volcanic eruptions, which results in a low signal to noise ratio, and this technique even works with less expensive instruments than typical high-precision GNSS stations, so it could provide a real-time, relatively inexpensive method for monitoring the plumes of shorter eruptions.
This innovative application demonstrates how GPS data can be analyzed in new ways to extract additional information about volcanic activity. The ability to detect ash plumes using existing GPS infrastructure adds value to monitoring networks and provides another tool for tracking eruptions in real-time.
Monitoring Volcanic Landslides and Flank Instability
At many large stratovolcanoes (for example, Mount Rainier), flank collapses and landslides are significant geologic hazards that may occur even in the absence of magmatic activity, and monitoring the stability of volcanoes is thus another critical application of geodetic monitoring networks to inform hazard assessment. GPS networks can detect slow-moving landslides and areas of instability on volcanic flanks, providing early warning of potential catastrophic failures.
The 1980 eruption of Mount St. Helens demonstrated the importance of monitoring volcanic deformation for detecting flank instability. In early 1980, a bulge appeared on the north side of Mount St. Helens, a volcano in the state of Washington; by late March, the bulge was growing almost 2 meters per day, and by May 17, the bulge had grown by over 130 meters. Modern GPS networks can detect such deformation much earlier and with greater precision, potentially providing more warning time for similar events.
Global Examples of GPS Volcano Monitoring
Hawaiian Volcanoes
The Hawaiian Volcano Observatory (HVO) operates one of the world’s most comprehensive GPS monitoring networks. HVO has over 70 permanent and continuously operating GPS stations on the Island of Hawai’i that gather data every day, plus, HVO scientists collect survey measurements at another 50 to 70 benchmarks for a couple days a year. This extensive network provides detailed coverage of Kīlauea, Mauna Loa, and other Hawaiian volcanoes, enabling scientists to track even subtle changes in volcanic activity.
The data from this network has contributed to numerous scientific advances in understanding volcanic processes. For over thirty years, high-precision GPS (Global Positioning System) measurements have been a key tool used by the USGS Hawaiian Volcano Observatory (HVO), and scientists have come to depend on daily GPS positions to monitor changes in the shape of volcanoes and understand magma storage and movement underground.
International Applications
GPS volcano monitoring has been successfully implemented at numerous volcanoes worldwide. From Mount Etna in Italy to volcanoes in Indonesia, Japan, and throughout the Pacific Ring of Fire, GPS networks provide critical data for volcano observatories. The aim of this project was to demonstrate that a continuous low-cost GPS monitoring system is an appropriate method for ground deformation monitoring to aid volcano studies. Studies at volcanoes like Mount Papandayan in Indonesia have demonstrated that effective GPS monitoring can be achieved even with limited resources.
The success of GPS monitoring at diverse volcanic settings has led to its adoption as a standard tool for volcano observatories worldwide. International collaboration and data sharing have further enhanced the value of GPS monitoring, allowing scientists to compare observations from different volcanoes and improve their understanding of volcanic processes globally.
Challenges and Limitations
Environmental and Technical Challenges
Despite its many advantages, GPS volcano monitoring faces several challenges. Harsh environmental conditions on volcanoes can damage equipment, requiring regular maintenance and replacement. Extreme temperatures, corrosive volcanic gases, heavy snowfall, and lightning strikes can all affect GPS station performance and longevity. Scientists must design robust installations that can withstand these conditions while maintaining measurement precision.
Signal interference and multipath effects, where GPS signals bounce off nearby surfaces before reaching the antenna, can introduce errors into measurements. Careful site selection and antenna design help minimize these effects, but they remain a consideration in network planning and data processing.
Data Interpretation Complexities
Interpreting GPS deformation data requires expertise and careful analysis. Not all ground deformation is caused by magma movement—tectonic processes, groundwater changes, landslides, and other factors can also cause surface displacement. Scientists must carefully analyze GPS data in conjunction with other monitoring information to correctly interpret the causes of observed deformation.
The relationship between surface deformation and subsurface magma movement is complex and not always straightforward. Mathematical modeling is required to infer the location, size, and behavior of magma bodies from surface measurements. These models involve assumptions and uncertainties that must be carefully considered when making eruption forecasts.
Coverage Limitations
GPS provides measurements only at specific point locations where receivers are installed. While networks can include dozens or even hundreds of stations, there are always gaps in coverage. This is where complementary techniques like InSAR become valuable, providing spatial coverage between GPS stations. However, the point-based nature of GPS means that localized deformation between stations might be missed without adequate network density.
Future Developments and Innovations
Advances in GPS Technology
GPS technology continues to evolve, with improvements in receiver sensitivity, processing algorithms, and data transmission capabilities. The expansion of satellite navigation systems beyond the U.S. GPS constellation—including Europe’s Galileo, Russia’s GLONASS, China’s BeiDou, and others—provides more satellites for positioning calculations, potentially improving accuracy and reliability. These Global Navigation Satellite Systems (GNSS) offer enhanced capabilities for volcano monitoring.
HVO upgraded their GPS data processing software to the latest program suite; it is designed to be more precise, accurate, user-friendly, and flexible, and HVO continues to be at the forefront of GPS data collection and processing to monitor the active volcanoes in Hawaii and American Samoa and to best understand their risks, while advancing scientific knowledge and hopefully reducing the negative impacts of volcanic eruptions.
Machine Learning and Automated Analysis
Artificial intelligence and machine learning algorithms are beginning to be applied to GPS volcano monitoring data. These tools can help identify subtle patterns in deformation that might be missed by traditional analysis methods, potentially improving eruption forecasting. Automated systems can process data in real-time and alert scientists to significant changes, enabling faster response to volcanic unrest.
Machine learning approaches can also help distinguish between different types of deformation signals, separating volcanic processes from tectonic movements, seasonal effects, and instrumental artifacts. As these techniques mature, they promise to enhance the value of GPS monitoring data and improve our ability to forecast volcanic eruptions.
Integration with Emerging Technologies
The future of volcano monitoring lies in the integration of GPS with other emerging technologies. Unoccupied aerial systems (drones) equipped with GPS can provide rapid mapping of volcanic features and changes. Fiber-optic sensing systems can complement GPS by providing distributed strain measurements. Advanced satellite systems offer improved temporal and spatial resolution for deformation monitoring.
The combination of these technologies with traditional GPS monitoring creates a comprehensive, multi-faceted approach to understanding volcanic processes. As computing power increases and data analysis techniques improve, scientists will be able to extract more information from GPS and related datasets, leading to better eruption forecasts and improved hazard mitigation.
Practical Applications for Hazard Mitigation
Early Warning Systems
GPS monitoring plays a crucial role in volcanic early warning systems. By detecting ground deformation that precedes eruptions, GPS networks provide valuable time for emergency managers to implement protective measures. This might include evacuating at-risk populations, closing access to hazardous areas, issuing aviation warnings, or activating emergency response plans.
The real-time nature of modern GPS monitoring means that warnings can be issued quickly as conditions change. This is particularly important for volcanoes near populated areas, where timely warnings can save lives and reduce economic losses. The integration of GPS data with other monitoring information provides a more reliable basis for decision-making during volcanic crises.
Long-Term Hazard Assessment
Beyond immediate eruption forecasting, GPS data contributes to long-term volcanic hazard assessment. By documenting patterns of deformation over years or decades, scientists can better understand a volcano’s behavior and identify areas at greatest risk. This information informs land-use planning, building codes, and infrastructure development in volcanic regions.
GPS monitoring also helps scientists identify previously unknown volcanic hazards. For example, the detection of flank instability through GPS measurements can reveal landslide risks that might not be apparent from other observations. This comprehensive understanding of volcanic hazards enables more effective risk management and community preparedness.
Supporting Scientific Research
The wealth of GPS data collected at volcanoes worldwide supports fundamental research into volcanic processes. Scientists use this data to test and refine models of magma chamber behavior, eruption triggering mechanisms, and volcanic plumbing systems. These insights advance our theoretical understanding of how volcanoes work, which in turn improves our ability to forecast eruptions and assess hazards.
GPS datasets from multiple volcanoes allow comparative studies that reveal common patterns and unique characteristics of different volcanic systems. This global perspective enhances our understanding of volcanic processes and helps identify which monitoring signals are most reliable for eruption forecasting at different types of volcanoes.
Conclusion
GPS technology has transformed volcano monitoring and the study of lava flows, providing unprecedented precision in measuring ground deformation and tracking volcanic activity. The ability to detect millimeter-scale movements in real-time has significantly improved our capacity to forecast eruptions and protect communities living near active volcanoes. From the comprehensive networks monitoring Hawaiian volcanoes to systems deployed at dangerous stratovolcanoes worldwide, GPS has become an indispensable tool for volcano observatories.
The advantages of GPS monitoring—including high precision, continuous operation, remote accessibility, and three-dimensional measurement capability—make it ideally suited for volcanic applications. When integrated with complementary techniques like InSAR, seismic monitoring, and gas measurements, GPS provides a comprehensive view of volcanic processes that enables more reliable hazard assessment and eruption forecasting.
As technology continues to advance and our understanding of volcanic processes deepens, GPS monitoring will play an increasingly important role in protecting lives and property from volcanic hazards. The ongoing development of more sophisticated analysis techniques, improved instrumentation, and better integration with other monitoring methods promises to further enhance the value of GPS for volcano science. For anyone interested in learning more about volcano monitoring techniques, the USGS Volcano Hazards Program provides extensive resources and real-time monitoring data.
The success of GPS volcano monitoring demonstrates the power of space-based technology to address critical challenges in Earth science and hazard mitigation. As we continue to refine these techniques and expand monitoring networks globally, we move closer to the goal of providing reliable early warning for volcanic eruptions, ultimately saving lives and reducing the devastating impacts of these powerful natural phenomena. Organizations like the EarthScope Consortium continue to advance geodetic monitoring capabilities, ensuring that volcano observatories have access to cutting-edge technology and expertise for protecting vulnerable communities worldwide.