Secondary Lahars Triggered by Periglacial Melting at Chimborazo Volcano, Ecuador

Periglacial melting processes can provide the water source for secondary lahars triggered by volcanic and/or meteorological phenomena on volcanoes. Between December 2015 and April 2016, four major lahars were reported southeast of Chimborazo volcano (Ecuador). Fieldwork allowed determining the area (1.670.37 km2), volume (3E+05 to 7E+05 m3), peak discharge (100 - 150 m3/s) and mean speed (2 - 4 m/s) of these flows, which affected the local infrastructure and threatened several towns downstream (>1000 inhabitants). This case study suggests that anomalous periglacial melting could have been induced by: i) an increase in temperatures at periglacial altitudes partly ascribed to El Niño phenomenon, ii) albedo reduction of the glacier due to ash fallout from Tungurahua volcano (40 km east of Chimborazo) which erupted from 1999 to 2016 and, iii) a slight increase in internal activity at Chimborazo prior and during the lahars occurrence, as evidenced by more seismic events and thermal anomalies. These simultaneous factors could have led to the formation, outburst and/or overflow of superficial and intra-glacier ponds providing the water source to generate lahars on a dormant volcano.