Topohazard, a novel tool for enhancing gravity-driven flows hazard maps: application to Cotopaxi volcano, Ecuador

Abstract During the 2015 volcanic crisis and eruption of Cotopaxi –one of Ecuador’s highest-risk volcanoes– an urgent issue arose concerning the integration of the 1:50,000-scale volcanic hazard map, developed in 2004, into digital applications supported by Geographic Information Systems. The incorporation of this lower-resolution map alongside newer, more detailed base cartography revealed critical inconsistencies between the drainage system and lahar hazard areas. To address this challenge, the Instituto Geofísico – Escuela Politécnica Nacional (IG-EPN) undertook a rapid update of the 2004 lahar hazard areas. This effort involved fieldwork to redefine the lahar hazard boundaries with greater precision and the development of a novel algorithm called Topohazard. The Topohazard algorithm provides a swift and efficient method for visualizing drainage morphology by generating a raster that highlights topographic differences relative to a user-defined Zero-Level Trajectory, such as a river channel. Leveraging the newly updated high-resolution Digital Elevation Model of Cotopaxi slopes available at the time, this innovative approach improved the understanding of terrain morphology and facilitated more accurate hazard boundary delineation. Through its application, combined with fieldwork, an updated version of the Cotopaxi volcanic lahar hazard map was released in 2016, which also included the previously unaddressed eastern drainage. This work explores the potential for highly detailed crisis management-oriented maps as a natural evolution of traditional volcanic hazard maps. The application of Topohazard in Latacunga is examined, including a discussion of its limitations, such as challenges posed by flat areas and abrupt changes in flow direction.