Fallout hazards associated with a possible renewal of explosive activity at Cerro Blanco volcanic complex, Austral Puna, Argentina.

WALTER BAEZ; ARNAU FOLCH; ANTONIO COSTA; JOSÉ VIRAMONTE

Puerto de la Cruz, tenerife

Congreso; Cities on Volcanoes 6; 2010

IAVCEI

Cerro Blanco volcanic complex is the youngest high-silica caldera complex of the Southern Central Andes. Two different periods of activity are identified. The first period (~72 ka BP) is characterized by voluminous ignimbrite-forming eruptions that generated the "Piedra Pomez" field (> 20 km3). At least one of these eruptions produced a tephra fallout .The second period (~20-15 ka BP) produced two smaller ignimbrite fields. During the last phase of the second period a dome was extruded at the caldera margins, and there were numerous phreatic explosions along a local fault system. At present there is some thermal activity and pipe and diffuse degassing at the center of the caldera. INSAR and high precision GPS measurements reveal that the system is currently subsiding at a rate of ~3 cm per year. Preliminary broadband seismic analysis indicates activity at ~7 km depth. Although the area around the volcanic complex is inhabited, a renewal of activity of the volcanic complex would have a tremendous impact on the region, especially in the more distal areas (>100 km) where several settlements exist. For these reasons, we investigated the effects of a potential tephra fallout eruption. On the basis of the volcanological records, we define two eruptive scenarios - violent strombolian and sub-plinian eruptions, respectively. For each scenario we assess the associated fallout hazard. Ash fallout is modeled using a semianalytical model and statistical wind field record. Simulations allow us to determine which areas could be affected, and the potential impact on main infrastructures, regional airports and national and international air traffic lines.