Analysis of the lahars associated with the 2011 Cordón Caulle eruption, Chile

In this study we analyse the lahar events in the area surrounding the Cordón Caulle volcano (Chile) occurred during the 2011 eruption. The main phase (4-6 June) was characterized by eruptive plumes from 7 to 11 km high which dispersed most of the tephra eastward toward Argentina, with a total estimated volume of about 1 km3. Tephra fall blanketed the region ESE and ENE from the volcano with thickness of the tephra layers between about 1 m (15 km from vent) and 0.06 m (240 km from the vent). On 10 June 2011, two lahars occurred close to the Argentina-Chile border; one lahar reached the National road 231 (at 26 km from the vent), while the second lahar reached the Provincial road 234 (65 km from the vent). At the same time, floods occurred in the town of Villa La Angostura (xx km) due to the high concentration of pyroclastic material in the river. An analysis of the lahars was carried out for the first 15 days of the eruption for the area between Cordón Caulle volcano and the town of Villa La Angostura. The spatial distribution of the potential lahar sources is modelled with an infinite slope stability model based on observed deposit grain-size and thickness, rainfall data and slope angle. Results are compared with the occurrence of lahar events during the 2011 Cordón Caulle eruption. These outcomes provide fundamental insights into lahar triggering during long-lasting volcanic eruptions and are crucial to the compilation of lahar hazard maps and emergency management plans in the South Andes volcanic region.