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Historical Distal Lahar Deposits on the Remote Eastern-Drainage of Cotopaxi Volcano, Ecuador

Abstract:

Cotopaxi is an active stratovolcano, located 60 km SE of Quito. During historical times, Cotopaxi experienced at least five eruptive cycles triggering major lahars which descended along all three main fluvial systems: Pita (north), Cutuchi (south) and Tambo-Tamboyaku (east). Northern and southern lahar deposits have been studied for decades, due to their impact on large populated areas. In contrast, the eastern deposits have only been occasionally mentioned. However, historical reports suggest that the AD 1744, 1768 and 1877 eruptions triggered lahars in the eastern drainage, which caused damage in this remote zone. These lahars flowed more than 120 km downstream crossing the uninhabited Eastern Cordillera until reaching the Amazon lowlands where rural-indigenous settlements were located. In this study, two different historical lahar deposits were recognized and characterized at the eastern lowlands. Several samples were collected in order to perform geochemical analyses of the juvenile blocks, grain size distribution, and componentry analyses of the proximal and distal eastern zones. Finally, inundation areas, deposit volumes and peak discharges were estimated. The results allowed us to make a detailed characterization of the deposits, which is valuable information for future investigations and which allows a better understanding of the potential consequences of a similar future event.