Understanding Taal Volcano for a better forecast of its next eruptions [fr]
Jacques Zlotnicki, Director of Research at the French National for Scientific Research (CNRS)
President of the scientific inter-association Electromagnetic Studies of Earthquakes and Volcanoes (EMSEV)
The Taal Volcano is a volcanic island located about 60 kilometers south of Manila. The edifice emerges at an altitude of 311 meters above Taal Lake, bordered by a vast prehistoric crater (caldeira). The region represents an important economic asset for the Philippines. Agriculture, aquaculture, tourism, resorts, and businesses allow about a million inhabitants to live within the 25 kilometer radius around Taal Volcano.
However, Taal is a dangerous volcano with frequent eruptions, 33 of which have been recorded since 1572. During an eruption, plumes of ashes and rocks avalanche rapidly downslope and devastate the outer flanks of the Island and a part of the Taal Lake, stopping at the rim of the prehistoric caldeira. In addition, ashes may be expelled up to an altitude of 15 kilometers into the atmosphere. The eruption of 1911 killed 1,500 inhabitants, and its ash clouds reached Manila. The last eruption in 1965 occurred outside the crater and devastated once again the southwest Island. Up to now, no eruption has been predicted sufficiently in advance to allow risk management and the protection of local communities.
After a conference on volcanic risks in Asia organized in 2003 by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the scientific inter-association Electromagnetic Studies of Earthquakes and Volcanoes (EMSEV), the development of an international cooperation was proposed, with the objectives to (1) understand and visualize with depth the volcanic structure, (2) decipher the eruptive dynamisms causing these eruptions, and (3) support PHIVOLCS in the monitoring of the volcano’s activity. Since 2004, a French team from the National Center for Scientific Research (CNRS) and a Japanese team from the Earthquake Research Institute in Tokyo have taken the leadership in the research, with the support of the Volcano Department of PHIVOLCS.
Since then, the teams - at least once a year - work together on the volcano and the update activity is discussed with PHIVOLCS. In the course of the first years, the teams have carried out electromagnetic surveys (a specialization of EMSEV) which have highlighted the internal structure of the volcano, the faults that take root at depth in the edifice, and the hydrothermal system (the zone where percolating ground water meets the ascending hot gases and fluids coming from the magmatic system below). The huge hydrothermal system located under the crater is located at about 2 kilometers in depth. The confluence between warm and cool fluids weakens the bedrocks by progressive mineralization. It can give rise to violent and rapid phreatic explosions once the pressure becomes too high.
The CNRS and their Japanese and US colleagues have also set up continuous recording stations for measuring several kinds of parameters: electric and magnetic fields, soil temperature, ground tilt, and the changes in the electrical resistivity of the subsoil, etc. These stations maintained by PHIVOLCS greatly assist the government agency in monitoring the volcanic activity. Since then, the teams have identified an extension of geothermal surface activity along ancient faults located on the northern flank and 2 kilometers away from the center of the crater. Finally, the most recent studies tend to show that longer the period between two eruptions is, the risk of a large explosion outside the crater increases, such as the 1965 eruption, which took place 54 years after the 1911 eruption. The current period is the third longest without an eruption.
These works will be presented during the international congress of the Asia Oceania Geosciences Society (AOGS) which will take place from February 4 to 8, 2018 in Tagaytay: http://nathazards.org/public.asp?page=home.htm. The main article, published in April 2017 in the Journal of Volcanology and Geothermal Research, is now available online.
Over the years, the international team has been reinforced by an American team specializing in the ground deformation (US Geological Survey), a Belgian team with an expertise in the geochemistry of fluids and gases (Free University of Brussels), and a Greek team specialized in electrical (University of Thessaloniki). The Japanese team has now mobilized many universities. In these scientific works which have a strong implication on the risks, the French team wishes to emphasize the support given by the Embassy of France in Manila throughout the years, regularly accompanying the researchers on the volcano and following the work carried out for a better understanding of the activity of Taal.