Brief Introduction to:

Thermal Infrared Remote Sensing of Active Volcanism-
Soufriére Hills, Montserrat


Remote sensing has fast become an important tool used for many applications from urban planning and development to sea surface temperature modeling. One application that is not as geographically pervasive, but ever increasingly important, is monitoring of active volcanoes. Location priority is not just given to volcanoes with a surrounding high population density, but also to those that are explosively eruptive and are currently in an active phase. Although Soufriére Hills, located in the Lesser Antilles on the island of Montserrat, is monitored heavily by the Montserrat Volcano Observatory, or MVO, remote sensing is still a critical method. Information using the ASTER satellite can be acquired by using bands from visible near infra-red to thermal wavelengths and beyond. Eventually, the knowledge gained from remotely monitoring Soufriére Hills will be applied to other locations as a hazard assessment and mitigation tool.

Volcanic landscapes have drawn attention for thousands of years. Not only do they provide an aesthetically pleasing backdrop, but most importantly provide rich soils for successful sustenance. Often, groups populate a hazardous area unknowingly due to the above reasons, ignoring warnings embedded in folklore. It is not very different today, however, even in our modern society with multiple forms of communication and a growing field of volcanology. People still inhabit regions where eruptions have taken place even in their own lifetimes. In some instances, efforts have been made to relocate populations, often to no avail. The people of Shimabara, Japan, for example, live in direct contact with pyroclastic flow pathways. The population has been estimated at 45,000, and with already crowded conditions, would be almost impossible to relocate. Instead, these people make a huge effort to control erupted material and practice mitigation protocols. Overall, the death toll from volcanoes and volcanic related phenomenon from 1600 until 1982 is 238,867, with pyroclastic flows being the number one killer (Tilling, 1989). An estimated 10% of the world’s population lives on or near dangerous volcanic areas, as estimated by Tilling in 1989. Recent estimates suggest 1 in 4 people can be subjected to volcanic hazards. With population densities increasing, identifying precursors to eruptions has become most critical for the mitigation efforts that ensue. Remote sensing can aid in this identification process.

The best way to understand volcanic activity is to observe and quantify eruptions first hand. Soufriére Hills is a stratovolcano on an active island-arc system. The volcano itself has became once again active in 1992, the first activity seen since earthquakes experienced in the 1960’s. In July of 1995, until the end of the year, phreatic explosions and ashfall were noted. Dome growth began in September of 1995, but did not produce pyroclastic flows until March of 1996. Since that stage of activity, until the present, dome growth and collapse has been fairly consistent. Other activity associated with dome growth at Soufriére Hills includes rockfall, ashfall, earthquake activity, and SO2 emission. Lahars are generated in accordance with heavier rainfall. Currently, 2/3 of the island is part of the Exclusion Zone. All of the activity is monitored by the MVO with a multitude of instruments, such as seismic stations and COSPECs, as well as by visual observations and fly-by’s. It is of course difficult and hazardous to obtain certain measurements, such as temperature, during an eruption. A satellite may capture an eruption at or near peak activity phase and allow some measurements to be safely taken. In the thermal wavelengths, radiant energy is a function of brightness temperature and emissivity. Using Planck’s constant, those two components can be derived. Monitoring temperature will allow some conclusions to be made about eruptive phase, as well as pre-eruption temperature flux.

In order to calibrate the remote sensing data, the most important factor would be to take direct measurements for comparison, on location. Global Positioning System points of the crater rim would allow thermal anomalies to be exactly placed, and measurements would provide a better understanding of peak eruption factors. Surface temperature plots in 3-D may offer a visual as to which areas of the dome are active in different stages. Continued monitoring via satellite and through the MVO are also key to understanding the capabilities of Soufriére Hills.