Canuti, P., N. Casagli, F. Catani, and G. Falorni, Modeling of the Guagua Pichincha volcano (Ecuador) lahars, Physics and Chemistry of the Earth, 27 (36), 1587-1599, 2002.
Abstract from the Paper:
Lahars, here defined as debris flows of volcanic origin, are rapid mass movements that pose a serious threat to cities located in the vicinity of many volcanoes. Quito, capital city of Ecuador and placed at the foot of the Pichincha volcano complex, is exposed to serious inundation hazard as part of the city is built on numerous deposits of large lahars that have occurred in the last 10,000 years. The objective of this paper is to model the potential lahars of the Pichincha volcano to predict inundation areas within the city of Quito. For this purpose two models that apply different approaches were utilized and their results were compared. The programs used were LAHARZ, a semi-empirical model conceived by the United States Geological Survey (USGS), and FLO-2D, a hydraulic model distributed by FLO Software Inc. LAHARZ is designed as a rapid, objective and reproducible automated method for mapping areas of potential lahar inundation (Proc. First Int. Conf. on Debris Flow Hazards Mitigation, San Francisco, USA, ASCE, 1998, p. 176). FLO-2D is a two-dimensional flood routing model for simulating overland flow on complex surfaces such as floodplains, alluvial fans or urbanized areas (FLO-2D Users manual, version 99.2). Both models run within geographical information systems (GIS). Fieldwork was focused on collecting all available information involved in lahar modeling. A total of 49 channel cross-sections were measured along the two main streams and stratigraphic investigations were carried out on the fans to estimate the volume of previous events. A global positioning system was utilized to determine the coordinates of each cross-section. Further data collection concerned topography, rainfall characteristics and ashfall thicknesses. All fieldwork was carried out in cooperation with the Instituto Geofisico of the Escuela Politecnica Nacional. Modeling in a GIS environment greatly aided the exportation of results for the creation of thematic maps and facilitated model comparison. Evaluation of the models was performed by comparing simulation results against each other and against the geometry of existing lahar deposits.
My Take:
Quito, capital of the country of Ecuador, is right in the path of the Pichincha volcanic complex lahar hazard zone. The authors of this paper used two computer models, LAHARZ, and FLO-2D for delineating the lahar inundation areas within the city of Quito. Those two models were chosen by the authors because they adopt completely different approaches to modeling lahars. They exported those models for use in ArcView, where they performed additional processing and comparison between the two models. The results obtained by the simulations carried out with LAHARZ and FLO-2D were compared with GIS to inundation areas of past events. The authors concluded that LAHARZ and FLO-2D provided results that differ noticeably. LAHARZ aims to rapidly provide indications concerning areas exposed to inundation hazard during emergencies while FLO-2D is proposed as a tool to be used in the middle and longterm management of areas prone to inundation. In this case, GIS provided a crucial mechanism for testing and comparing volcanic hazard models.