Caracterización geológica y petrográfica de los depósitos volcanoclásticos del volcán sumaco, provincia de napo y orellana; un aporte en la preparación del primer mapa de amenazas volcánicas del sumaco.

Abstract

The stratovolcano Sumaco is in northeastern Ecuador, between the provinces of Napo and Orellana. It has two scars indicating two major avalanches in its history, dividing the volcano into three parts: PaleoSumaco, Sumaco Actual, and Sumaco Reciente. A field study revealed a connection between Sumaco's previous eruptions and its sporadic eruptive activity. In the past 4400 years, there have been more regular eruptions with ash deposits extending over 20 km from the main crater, reaching a thickness of approximately 0.25 meters. Stratigraphic sections of the volcano's outer slopes revealed at least 4 major ash fall deposits associated with Sumaco's activity. These ash layers contain pumice with crystals of biotite, clinopyroxene, plagioclase, and traces of amphibole. Additionally, grayish rocks with phenocrysts of pyroxene and plagioclase of andesitic composition were found. Furthermore, three avalanche deposits (DAE-Guamaní, DAE-Payamino, and DAE-MPucuno), three lava flows (F.L-Pacto Sumaco, F.L-Pucuno Alto, F.L-Río Pucuno), four pyroclastic flow deposits (F.P Oritoyacu, F.P. Río Sapo, F.P Pucuno Alto, F.P. Sendero Pacto Sumaco), and one pyroclastic surge flow (F.P-JP12-Sendero Pacto Sumaco) were identified. In conclusion, this study linked these deposits to the three structural phases of the current cone formation of Sumaco Volcano, using geochemical, granulometric, petrographic analyses, and radiocarbon dating on carbonized plant remains found in the deposits.