Caracterización granulométrica del Lahar del Valle de los Chillos (CVL) en el flanco norte del volcán Cotopaxi.

Abstract

Cotopaxi is a large active stratovolcano located in the eastern cordillera of the Ecuadorian Andes, between the provinces of Pichincha and Cotopaxi. The present edifice, approximately conical, is the result of innumerable eruptions that occurred in the past. Due to its glacial cover, primary lahars have been very common phenomena recorded in all the eruptive cycles of the last 2,000 years. Approximately 4,500 years BP, the last catastrophic rhyolitic eruption occurred, which caused the sectoral collapse of the volcano, generating to a huge avalanche of debris and followed by an enormous lahar called "The Chillos Valley Lahar" (CVL), which descended through its northern fluvial system to the Pacific Ocean. This research seeks to study the lahar through granulometric characterization and geological mapping. The data provided for this study were analyzed based on statistical parameters that more accurately describe the grain size distribution of the components. The granulometry of the CVL deposit shows that the sand size grains are the dominant fraction with 49.4 wt. %. Samples from the CVL deposit fall into the category of “non-cohesive debris flows”, which are characterized as poorly sorted, massive, and generally matrix supported. The observation routes allowed us to confirm that the deposit is homogeneous and lacks internal gradation. In the study area, the deposit extends over an approximate area of 388 km2; Therefore, a dry volume of approx. 0.77 km3.