Estimation of precipitation thresholds that cause laharic phenomena in the Concepción volcano, Ometepe island, Rivas, 2016

Abstract

Lahars are flows made up of sediments and water that move on volcanic slopes, highly destructive due to the great speed they take and their high density of materials. This research estimates the triggering precipitations that have caused the laharic phenomena in the Concepción volcano, Ometepe Island, 2016, to provide data that contribute to the design of an early warning system before the occurrence of this phenomenon. Initially, meteorological stations were installed to obtain the rainfall record during 2016 and, in turn, the laharic events that occurred during this year were monitored. Subsequently, correlating the data between the date and time of lahar occurrence with the precipitation recorded at the triggering moment, an estimate was made of the triggering precipitation thresholds for each laharic event associated with the accumulated rainfall of the previous 30 days. The results indicate that eight laharic phenomena occurred in 2016, these events originated in areas made up of unconsolidated lavas. The unconsolidated lava where these events originated refers to fragmented materials of different diameters (pyroclastic), including fine material such as ash, when this material becomes supersaturated, its volume and specific weight increase and it tends to destabilize and destabilize thicker materials, which, added to the high slopes of the Concepción volcano (up to 100%), increases the susceptibility of lahar-type landslides. Of the eight laharic phenomena that occurred, four are the events for which there is a record of rainfall greater than zero millimeters, these events occurred on average with triggering rainfall of 35.88 mm and intensities of 19.57 mm h^-1, with accumulated rainfall on previous days of 0.76 mm (one day), 29.45 mm (10 days), and 150.03 mm (30 days).