Comment on: “Cobeñas, G., Thouret, J.-C., Bonadonna, C., Boivin, P., 2012. The c.2030 yr BP Plinian eruption of El Misti volcano, Peru: Eruption dynamics and hazard implications. Journal of Volcanology and Geothermal Research 241-242, 105-120.”

Abstract

Cobeñas et al. (2012) describe deposits from the 2-ka eruption of Misti volcano, southern Peru. They propose a tephra-fall deposit overlain by voluminous pyroclastic-flow and surge deposits, which are overlain by proportionally minor lahar deposits and a debris-avalanche deposit of limited distribution. Some of their data corroborate our earlier work (Harpel et al., 2011), but three of their primary interpretations differ dramatically from ours and have important hazard implications. Voluminous flowage deposits crop out, and we present evidence that the majority contain diagnostic features suggesting that they are lahar deposits rather than pyroclastic-flow deposits. Their pyroclastic-flow deposit volume is also unrealistically large and not consistent with the extant deposits. The purported debris-avalanche deposit is texturally identical to the lahar deposits and has none of the features typically associated with debris-avalanche deposits. Associating such a unit with collapse and formation of a notch in the south crater rim lacks supporting data and disregards the myriad other reasons such notches can form. They divide the tephra-fall deposit into three beds, suggest that it underlies the pyroclastic-flow deposits, and infer that the eruption ceased after pyroclastic flow formation. We delineate six beds and present evidence that the upper beds persistently crop out between the pyroclastic-flow and lahar deposits. We infer from our eruption sequence that the eruption continued vigorously after pyroclastic-flow formation.