Copahue volcano activity and increasing population in Caviahue village (eastern flank), North Patagonia Andes

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Rovere, Elizabeth Ivonne۱; Poscolieri, Maurizio۲
Holding Date 03 September 2008

Caviahue Volcanic Complex constitutes a series of volcano-tectonic centers and an asymmetric 20 x 18 Km caldera located eastward of the active volcano: Copahue. During year 2000, Copahue volcano acid crater lake collapsed as a precursor of over 50 explosions of low intensity (VEI 1 to 2) occurred during 5 months. Since 2001, Caviahue village has received more than 50,000 tourists and the local population has been continuously increasing. Geological records indicate high explosive index (VEI>3) within the last three million years, in six different episodes (at least): 2,63 Ma (Riscos Bayos; ignimbrite I), 2,08 Ma (Riscos Bayos; ignimbrite II), 1,1 - 0,9 Ma (Domo Acido; rhyolite), 0,76 Ma (Copahue Volcano; dacite) and 0,62 Ma (Cerro Bayo rhyolite). Probably, higher eruptive explosions occurred after 0,62 Ma, but reliable age dating methods in volcanic rocks after Mid-Pleistocene to pre-history are still in debate.
Furthermore, historical records are scarce in this Andean region. Last eruptions generated a 15 m high wall in the crater rim, and about 4 Km2 of unconsolidated volcaniclastic blocks around the summit. The eastern flank of Copahue is unstable and can be shot by a low phreatomagmatic explosion or by drastic climatic changes such as an intense snow or rain, or even by melting the western rim glacier through increasing warming. The risk is focused to tourists or local population of Caviahue and Copahue villages. Two exit roads from Caviahue and Copahue exist, both cross the volcano valleys, only the southern way is paved. In case of an eruption, a pyroclastic flow or a lahar would cross the route through the valleys (and cross the small bridge) after 20 minutes. Lake physical chemical monitoring, together with seismic and acoustic emission measurements are in a progress program of multidisciplinary characteristics. Further research studies are necessary, particularly on flank instability and anomalous flows drainage predictions.