Enormous and far-reaching debris avalanche deposits from Sangay volcano (Ecuador): Multidisciplinary study and modeling the 30 ka sector collapse

Abstract Sangay is one of the most active volcanoes in the world. Its eruptions were first recorded by Spanish priests in 1628, and since 2010 it has displayed VEI 1–2 level eruptive activity about every two years. Its most recent eruptive phase began on May 7, 2019, and has continued until the present. While most eruptive products do not impact inhabited areas, Sangay's associated Pleistocene-age avalanche deposits were enormous and far-reaching. Their surfaces are now populated by numerous communities on the volcano's E and SE aprons. The study of Sangay's debris-avalanche deposits located in SE Ecuador in the upper Amazon Basin indicates at least two avalanche events. Sangay Debris Avalanche-1 is the first deposit (250–100 Ka, as reported by Monzier et al., 1999 ), and Sangay Debris Avalanche-2 the younger deposit (~30 Ka, 14C dated). Both avalanches have a run-out distance of more than 60 km from Sangay's central crater. Statistical analysis of 541 counted hummocks shows that the largest hummocks are located in the middle run-out zone, between 40 and 50 km from the volcano. This middle zone possibly indicates that while in transport, the younger avalanche impacted laterally with a 500 m high ridge located SE of the volcano. The flow was redirected around this elevated, uplifted morphology. Petrological and geochemical data of clasts from the avalanche deposits have a similar affinity with late Holocene primary eruptive products from Sangay volcano. The vertical relief, mapped area, run-out distance, and the estimated deposit volumes categorize the two Sangay debris avalanche deposits as some of the furthest reaching volcanic slides related to continental volcanoes. Numerical simulations indicate that Sangay's potential future flank collapse could produce large debris avalanche deposits directed to the East, occupying the northern and southern drainage networks around the volcano. Several localities and towns would be affected, and the flow of major rivers would be blocked, and subsequent secondary lahars could have important discharges (1000 to 10,000 m3/s). We performed numerical simulations using the VolcFlow code, applying rheological parameters (plastic retarding stress of ~50 kPa) to simulate possible future debris avalanches of Sangay volcano.