Awakening
Awakening of Mount Chaitén, a forgotten volcano
During the evening of April 30th 2008, in a distant volcanic region in the southern Andes about 1000 km south of Santiago, Chile, strong ground shaking was the first sign that something was awry. Thousands of people felt an increasing number of strong earthquakes that just would not quit. On May 2nd Mount Chaitén , in southern Chile, interrupted a period of quiescence of more than 9000 years generating a sequence of explosive eruptions that caused the spontaneous evacuation of the 4’700 residents of Chaitén town located about 10 kilometers south of the volcano. Chaitén is the gateway for Chilean tourism in Patagonia and a center of commercial salmon aquaculture. Other people within 50 km of the volcano were also promptly evacuated by the Chilean government.
For about a week, Mount Chaitén generated several eruptive plumes up to about 20 km above sea level and dispersed volcanic ash up to the Atlantic coast of Argentina about 600 km east of the volcano disrupting various human activities, contaminating ground water supplies and seriously affecting agriculture and aviation. On the 13th May a first fast-moving mud flow (i.e. lahar) reached Chaitén town destroying everything on its path and finally entering the ocean. After the first couple of weeks of May 2008, the activity at Mount Chaitén has been characterized by dome explosions and dome collapses of lower magnitude and intensity, but life around Mount Chaitén is still largely affected by the dispersal and accumulation of volcanic ash (a regular update is provided by the Global Volcanism Program of the Smithsonian Institution). The eruption of Mount Chaitén is characterized by a very particular type of magma (i.e. rhyolite) that does not erupt very frequently (the last rhyolitic eruption before Chaitén was the 1912 eruption of Novarupta volcano, Alaska). As a result, this eruption requires detailed studies not only for the identification of potential hazards for the surrounding areas but also because it could reveal crucial insights into eruption dynamics.
In January 2009 a team of scientists from the volcanology group of the University of Geneva has been to southern Chile together with a team of scientists from the University of South Florida (USA) and a team of scientists from the University of Oxford (UK) in order to accurately characterize the tephra deposit generated by Mount Chaitén and assess the potential hazards associated with the current eruption. As a result of this trip, we have indentified individual tephra layers associated with the May 2008 eruption that could be correlated with the corresponding satellite images. The volume of the largest events was derived together with other crucial parameters (e.g. granulometry, plume height, mass discharge rate, duration). All this parameters are necessary for the compilation of a hazard assessment, which is still in progress. In fact, a dedicated model for the description of the dispersal of tephra can be used in combination with comprehensive information on wind conditions to provide a probabilistic assessment of possible dangerous tephra accumulation around the volcano (e.g. (TEPHRA model). Probabilistic hazard assessments are crucial to land-use planning. In addition, probabilistic hazard assessments can be associated with various aspects of vulnerability to produce detailed risk evaluations. The volcanology/geological risk group of the Department of Mineralogy (Section of Earth and Environmental Sciences) is largely involved in the study and identification of new strategies for risk reduction including:
- an international program for the evaluation and management of geological risks (i.e. CERG);
- a European effort for the development of a new methodological framework for an integrated multi-scale vulnerability assessment (i.e. ENSURE);
- a CERG-UNOSAT joint project for the development of a new methodology for a fast risk assessment of active volcanic areas.
C. Bonadonna