© D. Gibert Helicopters lowered scientists and their equipment on the Tarissan crater of La Soufrière volcano.
© D. Gibert
Helicopters lowered scientists and their equipment on the Tarissan crater of La Soufrière volcano.
Digital models are extremely helpful and currently used in a variety of fields that can range from archaeology to epidemiology. Scientists now plan to synthesize different geophysical, geochemical, and hydrology models into a single model of digital volcano. The volcano chosen to design this model is La Soufrière, on the French
To create this ideal model, scientists first had to gather data directly on the volcano (sometimes by being lowered on cables from hovering helicopters). This was the purpose of a campaign1 that started May 29th and ended at the beginning of summer, before weather conditions deteriorated. Researchers completed a plethora of measurements to study all aspects of the volcano. “Our approach can be compared to that of medical imagery,” explains Dominique Gibert,2 heading the project which involves numerous CNRS laboratories.3 “Structural imagery is used to study the architecture of the volcano and development, while functional imagery makes it possible to observe, understand, and predict its internal activity.”
To kick off this campaign, the researchers first scrutinized the volcano by covering its north-west flank with cables and sensors, despite rubble from the massive collapse caused by the Saintes earthquake in 2004.4 Physicists then remeasured certain volcano profiles to examine how they evolved over time. This was mainly achieved using electric tomography, which, by inputting an electrical current at different points, provides 3D knowledge of the structure, and also gives an insight into subterranean activity. “Data show strong hydrothermal reactivation under La Soufrière volcano,” explains Gibert. And there is another worrying sign: “Fifteen years ago, we could enter the Tarissan crater, at the top of the dome where the temperature reached 40°C. Today, it has soared to 100°C.” This rise in activity could be confirmed by parallel analyses, including measurements of fluctuations in carbon dioxide emissions from the faults. These are magmatic in origin, and large amounts of gas attest to increasing volcanic activity. “On the other hand, this increased activity does not necessarily indicate an upcoming eruption,” the physicist was quick to point out. Moreover, the main danger is not necessarily an eruption: “The collapse of the dome represents a greater threat,” he continues. “In fact, geologists are aware that this area is highly unstable with a tendency to shift. And if the 150 million cubic meters of the dome cave in, this could definitely trigger an eruption.”
> See the model
1. Carried within the framework of the “Structure et stabilité de la zone sommitale de la Soufrière de Guadeloupe” (Structure and stability of the summital zone of the Guadeloupe Soufrière) project.
2. Dominique Gibert, from the Géosciences Rennes laboratory (CNRS / Université Rennes-I joint lab), heads this project along with Georges Boudon, Director of the volcanic observatories of the Institut de physique du globe de Paris (IPGP: Paris Institute for Global Physics).
3. Laboratoire Géosciences Rennes (Geoscience Laboratory-Rennes), IPGP, LGIT, Magma and volcano laboratory, Pierre Süe Laboratory, LSCE, IUEM, LDG (CEA).
4. For more information on seismic activity in Guadeloupe, visit www.ipgp.jussieu.fr