LLUNPIY Simulations of the 1877 Northward Catastrophic Lahars of Cotopaxi Volcano (Ecuador) for a Contribution to Forecasting the Hazards

Abstract

LLUNPIY (lahar modeling by local rules based on an underlying pick of yoked processes, from the Quechua word “llunp’iy“, meaning flood) is a cellular automata (CA) model that simulates primary and secondary lahars, here applied to replicate those that occurred during the huge 1877 Cotopaxi Volcano eruption. The lahars flowing down the southwestern flanks of the volcano were already satisfactorily simulated in previous investigations of ours, assuming two possible different triggering mechanisms, i.e., the sudden and homogeneous melting of the summit ice and snow cap due to pyroclastic flows and the melting of the glacier parts hit by free-falling pyroclastic bombs after being upwardly ejected during the volcanic eruption. In a similar fashion, we apply here the CA LLUNPIY model to simulate the 1877 lahars sprawling out the Cotopaxi northern slopes and eventually impacting densely populated areas. Our preliminary results indicate that several important public infrastructures (among them the regional potable water supply system) and the Valle de Los Chillos and other Quito suburban areas might be devastated by northward-bound lahars, should a catastrophic Cotopaxi eruption comparable to the 1877 one occur in the near future.

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

“…Conversely, the 1877 calibration simulations obtained with LLUMPIY [30] are significantly different from the cartography of this study. One of the main reasons for such differences may be related to another finding highlighted here.…”

“…Such differences are explained by the topography of the summit crater, whose northern rim is ~120 m higher than its eastern rim, which produced that only the more diluted bomb-depleted PDCs descended northwards, while the denser bomb-rich PDCs descended towards the East. However, one of the main assumptions made in [30] during LLUMPIY calibrations, is that PDCs (and consequently primary lahars) are evenly distributed all around the crater rim, which ultimately produces the differences between the calibration simulations and the cartography obtained here.…”

“…Thus, in the simplest approach, the results of the present study could be useful to improve the calibration of new generation models such as RAMMS or LLUMPIY [29,30]. This means that the adjustment of parameters governing any 1877 model should be such that the produced simulations are at least somewhat similar to the cartography presented here, considering that the current day topography might be significantly different from that prior to 1877 and, as already discussed, the cartography presented here only represents the current day lithic deposit left since the original event.…”

“…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.…”