Modelling future lahars controlled by different volcanic eruption scenarios at Cotopaxi (Ecuador) calibrated with the massively destructive 1877 lahar

Abstract

Lahars are among the most hazardous mass flow processes on earth and have caused up to 23 000 casualties in single events in the recent past. The Cotopaxi volcano, 60 km southeast of Quito, has a well-documented history of massively destructive lahars and is a hotspot for future lahars due to (i) its $10 km 2 glacier cap, (ii) its 117-147-year return period of (Sub)-Plinian eruptions, and (iii) the densely populated potential inundation zones (300 000 inhabitants). Previous mechanical lahar models often do not (i) capture the steep initial lahar trajectory, (ii) reproduce multiple flow paths including bifurcation and confluence, and (iii) generate appropriate key parameters like flow speed and pressure at the base as a measure of erosion capacity. Here, we back-calculate the well-documented 1877 lahar using the RAMMS debris flow model with an implemented entrainment algorithm, covering the entire lahar path from the volcano edifice to an extent of $70 km from the source. To evaluate the sensitivity and to constrain the model input range, we systematically explore input parameter values, especially the Voellmy-Salm friction coefficients μ and ξ. Objective selection of the most likely parameter combinations enables a realistic and robust lahar hazard representation. Detailed historic records for flow height, flow velocity, peak discharge, travel time and inundation limits match best with a very low Coulomb-type friction μ (0.0025-0.005) and a high turbulent friction ξ (1000-1400 m/s 2). Finally, we apply the calibrated model to future eruption scenarios (Volcanic Explosivity Index = 2-3, 3-4, >4) at Cotopaxi and accordingly scaled lahars. For the first time, we anticipate a potential volume growth of 50-400% due to lahar erosivity on steep volcano flanks. Here we develop a generic Voellmy-Salm approach across different scales of high-magnitude lahars and show how it can be used to anticipate future syneruptive lahars.

Community Perception and Communication of Volcanic Risk from the Cotopaxi Volcano in Latacunga, Ecuador

“…Therefore, this work is providing the community with the availability of scenario-based risk models based on the vulnerability of the exposed elements in graphical and user-friendly interphase, which is an added value for the local community. The integrated scenario-based lahar footprints per VEI [69] and the locally developed probabilistic ash falls models [95] are themselves useful outcomes for civil protection and local-planners. They can be used to identify which human settlements and agricultural plantations might be affected or even discuss the relocation of some of the exposed components of critical infrastructure.…”

“…The iteratively constructed RIESGOS demonstrator for a multi-risk information system is based on a modular and scalable concept in which the different hazards, the related exposure models, and vulnerability schemas are each represented by one individual web service. These independent and distributed web-services (managed and maintained by individual research institutions) are based on the quantitative methodologies developed within the RIESGOS framework for multi-risk analysis (i.e., [69,[89][90][91][92][93][94]). Therefore, their integration into the RIESGOS demonstrator simulates the multi-risk environment of Latacunga.…”

“…They are represented by isolines ( Figure A1). The lahar models described in [69] are incorporated, showing the maximum possible values of five physical properties (i.e., flow velocity, flow depth, pressure, erosion, and deposition (see Figure A2). Figure 6.…”

Detailed Cartography of Cotopaxi’s 1877 Primary Lahar Deposits Obtained by Drone-Imagery and Field Surveys in the Proximal Northern Drainage

“…The main findings of the present study should be taken into account when lahar hazard at Cotopaxi is re-assessed with improved numerical models in the future. Two of the most recent and developed numerical approaches tested for lahar hazard assessment at Cotopaxi are based on: the numerical solution of fluid-dynamics partial differential equations that represent lahars by a Voellmy-Salm reology (RAMMS software) [29]; and, the use of a multicomponent Cellular Automata of semiempirical models of surface flows (LLUMPIY model) [30]. Both are 3D models capable of simulating phenomena such as erosion and deposition of the moving flow, as well as providing fundamental quantitative information (i.e., for further risk assessment) such as basal, lateral and impact pressure, or flow height and average velocity at any point of a high-resolution drainage topography.…”

“…Thus, the lahar hazard at Cotopaxi has always been assessed by deterministic approaches, which have used different numerical models calibrated with field data and corresponding lahar scenarios. Numerical models tested at Cotopaxi include 1-D hydrological [7,16,27,28], statistical [18], and more developed flow-dynamics-based codes which consider deposition, bulking and erosive processes [29,30]. Regardless of the numerical model, the field data or lahar scenario used as either entry data, boundary condition, or calibration, has been invariably derived from knowledge of the primary lahar that occurred on 26 June 1877, during the latest highly explosive eruption of the Cotopaxi volcano.…”