Evaluation of the initial stage of the reactivated Cotopaxi volcano – analysis of the first ejected fine-grained material

Abstract. Fine-grained volcanic samples were collected at different locations near the Cotopaxi volcano on the same day of its reactivation and some days afterwards in August 2015. The wind-directions charged with such materials have been determined and compared with the existing data-base allowing preventive measures about local warning. The obtained data yielded the less expected wind-directions and therefore ash precipitation in usually less affected areas towards the northern and eastern side of Cotopaxi volcano. The collected samples were studied basically for their morphology, content in minerals and rock fragments as well as the chemical composition. The results obtained from this study allowed to identify and classify the origin of the expelled material being hydroclasts of andesites and dacites with rare appearances of rhyodacites and associated regular as well as accessory minerals all being present in the conduct and crater forming part of previous eruptive activities of the volcano. A further evaluation has been performed to determine the activity stage of the volcanic behavior. The resulting interpretation appears to point to a volcanic behavior a more frequent sporadic event with a relatively low probability of lahar generation rather than any other known destructive phase, which includes a less-frequent but tremendously more catastrophic scenario.