Monitoring natural hazards is fundamental to public safety and disaster preparedness. Volcanic eruptions and powerful storms like hurricanes can cause widespread devastation, but modern science provides tools to observe and track these phenomena. Scientists rely on a complex suite of technologies, from instruments placed directly on a volcano’s slopes to satellites orbiting the planet, to gather necessary data. This continuous stream of information allows for the prediction of hazard timing, trajectory, and intensity, giving communities time to prepare and evacuate.
Monitoring Volcanic Activity: Ground-Level Geophysical Tools
Magma movement beneath a volcano causes minute changes in the ground surface measured by high-precision instruments. Ground deformation is tracked using networks of Global Positioning System (GPS) receivers. These measure the distance between fixed points to detect if the volcano is bulging outward. This inflation, often only a matter of centimeters, signals rising magma or increasing pressure in a shallow reservoir beneath the surface. Highly sensitive tiltmeters record the slightest changes in the ground’s slope. Strainmeters, buried deep in boreholes, measure the tiny stretching or squeezing of the crust caused by the pressurized magmatic system.
Seismic monitoring provides immediate evidence of activity deep within the volcano’s plumbing system. Seismometers record two main signals: discrete volcano-tectonic earthquakes and continuous volcanic tremor. The small, sharp earthquakes result from the surrounding rock fracturing under stress as magma forces its way upward through cracks and fissures. Volcanic tremor, a low-frequency, rhythmic shaking, is associated with the movement of magma or volcanic gas through conduits. Deploying a network of seismometers allows scientists to pinpoint the location and depth of the unrest, mapping the magma’s migration path.
The composition and volume of gases released from fumaroles and vents offer chemical clues about the magma system. Sulfur dioxide (\(\text{SO}_2\)) and carbon dioxide (\(\text{CO}_2\)) are the two primary magmatic gases monitored. Correlation Spectrometers (COSPEC) or newer UV-based spectrometers are used to measure the total flux of \(\text{SO}_2\) in the volcanic plume as it passes overhead. Sudden increases in \(\text{SO}_2\) emission often precede an eruption, as it is a volatile gas that separates from the magma close to the surface. Ground-level sensors, such as those in a Multi-GAS system, also measure the ratio of \(\text{CO}_2\) to \(\text{SO}_2\) to determine if new, gas-rich magma is rising from depth.
Monitoring Volcanic Activity: Satellite and Aerial Observation
For a broader, non-invasive assessment of volcanic unrest, scientists rely on remote sensing instruments aboard satellites and aircraft. Interferometric Synthetic Aperture Radar (InSAR) is a satellite-based technique that measures ground deformation across wide areas with millimeter-scale accuracy. This method uses radar waves to compare two images of the same area taken at different times. Ground movement appears as a pattern of colored fringes in a resulting image called an interferogram. InSAR is effective for tracking the slow inflation or deflation of a volcano, especially in remote regions.
Thermal monitoring uses satellite-borne infrared sensors to detect and measure heat radiating from the volcano’s surface. These sensors identify thermal anomalies, such as new lava flows, hot craters, or changes in fumarole field temperature. Systems automatically process this data to provide near-real-time detection of high-temperature hot spots. This information is useful for tracking the effusive activity of an ongoing eruption and quantifying the energy output.
Tracking the atmospheric dispersal of volcanic clouds uses satellite-based spectrometers operating in the ultraviolet and infrared spectrums. These instruments measure the total column of volcanic gases, especially \(\text{SO}_2\), and ash in the eruption plume. This data is essential for aviation safety, as volcanic ash clouds pose a severe threat to jet engines. By mapping the three-dimensional structure and movement of the plume, forecasters issue warnings to reroute air traffic away from hazardous areas.
Tracking Hurricanes: Atmospheric and Oceanic Data Acquisition
Direct measurement of a hurricane’s environment is necessary to understand its current state and potential for intensification. This data acquisition involves specialized aircraft reconnaissance missions, often flown by “Hurricane Hunters.” These planes fly directly into the storm’s eye and eyewall to gather high-resolution, in-situ atmospheric data. Data is collected by dropping expendable devices called dropsondes, which descend to the ocean surface.
As dropsondes fall, they transmit a vertical profile of the atmosphere, measuring pressure, temperature, humidity, and wind speed and direction. The minimum sea-level pressure recorded in the eye is a primary indicator of the storm’s intensity. This detailed profile data is immediately transmitted back to forecasters. The observations provide a precise, three-dimensional snapshot of the storm’s structure, which is crucial for improving numerical weather prediction models.
Oceanic conditions provide the energy source that fuels a hurricane’s development. Tropical storms draw power from the heat stored in the upper layers of the ocean, known as Ocean Heat Content (OHC). Argo floats are autonomous, deep-diving instruments that measure temperature and salinity at various depths, providing the subsurface data necessary to calculate OHC. Weather buoys and drifting surface buoys complement this by measuring Sea Surface Temperature (SST), atmospheric pressure, and waves in real-time. The depth of the warm water layer is important because if it is deep, the storm’s churning action fails to mix cooler water to the surface, allowing the hurricane to strengthen rapidly.
Tracking Hurricanes: Remote Sensing and Prediction Systems
The large-scale visualization and tracking of hurricanes rely on satellite remote sensing and advanced ground-based radar systems. Weather satellites operate in two primary orbits. Geostationary satellites, such as the GOES series, orbit at a high altitude and move at the same rate as the Earth’s rotation, remaining fixed over a specific point on the equator. This fixed perspective provides a continuous view of a hemisphere, enabling forecasters to track the real-time movement and development of a storm every few minutes.
Polar-orbiting satellites fly at a lower altitude and travel from pole to pole, with the Earth rotating beneath them. These satellites provide global coverage and collect highly detailed atmospheric temperature and moisture profiles, which are crucial for long-range forecast models. Although they observe a specific location less frequently, their higher resolution data significantly improves the accuracy of the storm’s initial conditions used in prediction models. Together, these two types of satellites offer continuous surveillance and the detailed atmospheric input required for accurate forecasting.
As a hurricane approaches land, ground-based and airborne Doppler radar systems provide high-resolution data on the storm’s structure and internal wind field. Doppler radar works by emitting microwave pulses and measuring the slight change in frequency of the signal returned by precipitation particles, known as the Doppler shift. This measurement allows the estimation of wind speed and direction within the storm, helping to visualize the eye, eyewall, and rainbands. The data is integrated into complex Numerical Weather Prediction (NWP) models. These models use supercomputers to solve the mathematical equations governing the atmosphere and ocean, generating ensemble forecasts that predict the hurricane’s track and intensity over the next several days.