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Análisis Cuantitativo Del Riesgo De Inundación Por UNIVERSIDAD DE CHILE FACULTAD DE CIENCIAS FÍSICAS Y MATEMÁTICAS DEPARTAMENTO DE GEOLOGÍA ANÁLISIS CUANTITATIVO DEL RIESGO DE INUNDACIÓN POR LAHARES EN EL VOLCÁN VILLARRICA: MÉTODOS INTEGRADOS DE PELIGRO Y VULNERABILIDAD PARA LA CIUDAD DE PUCÓN, CENTRO SUR DE CHILE MEMORIA PARA OPTAR AL TÍTULO DE GEÓLOGO FELIPE ANDRÉS FLORES LOBOS PROFESOR GUÍA LUIS ENRIQUE LARA PULGAR MIEMBROS DE LA COMISIÓN ANGELO CASTRUCCIO ALVAREZ OSCAR GABRIEL OROZCO LANFRANCO SANTIAGO DE CHILE DICIEMBRE 2014 RESUMEN DE LA MEMORIA PARA OPTAR AL TÍTULO DE: Geólogo POR: Felipe Andrés Flores Lobos Fecha: 01/12/2014 PROFESOR GUÍA: Luis E. Lara Pulgar ANÁLISIS CUANTITATIVO DEL RIESGO DE INUNDACIÓN POR LAHARES EN EL VOLCÁN VILLARRICA: MÉTODOS INTEGRADOS DE PELIGRO Y VULNERABILIDAD PARA LA CIUDAD DE PUCÓN, CENTRO SUR DE CHILE El Volcán Villarrica (39°25′12″S, 71°56′23″W, 2.847 msnm) es un estratovolcán del centro sur de Chile, desarrollado durante el Pleistoceno superior y el Holoceno, y que ha emitido productos principalmente de composición basáltica a andesítico – basáltica. Sus más de 60 erupciones registradas desde 1558, lo convierten en uno de los volcanes más activos de Chile y Sudamérica, y su extensa cobertura glacial y nival, con un volumen equivalente en agua estimado en 2,7 km3, hacen que la generación de lahares o flujos de detritos volcánicos sea uno de los procesos más peligrosos para la zona aledaña al volcán. En este contexto se ubica la ciudad de Pucón, a cerca de 16 km del cráter, y que se encuentra rodeada por quebradas que drenan al Villarrica y que representan caminos para los flujos laháricos, como lo son la quebrada Zanjón Seco, el río Turbio y el Pedregoso. El presente trabajo realiza un análisis cuantitativo del riesgo de inundación por lahares para la comuna de Pucón; esto se logra por un lado, evaluando el peligro, mediante la utilización del modelo numérico Laharz, que simula las áreas inundadas en función del volumen inicial del flujo para distintos escenarios eruptivos, cada uno con una frecuencia esperada, y además incorporando criterios geológicos, hidrológicos y geomorfológicos; y por otro lado, evaluando la vulnerabilidad en base a 3 parámetros sociodemográficos como son (1) los grupos etarios y la proporción de discapacitados, (2) la densidad de población, y (3) el grado de escolaridad. Los resultados muestran que existen zonas bajo alto o muy alto riesgo, en los sectores de Quelhue, El Turbio, y el sector sureste del área urbana de Pucón. En cuanto a la metodología, dadas las limitaciones del modelo numérico para evaluar el peligro, y a su alta sensibilidad frente al modelo de elevación digital (DEM), se propone una metodología combinada, basada en la cuantificación de las áreas de inundación entregadas por el modelo Laharz, y también en la interpretación geológica del lugar. Palabras claves: Lahar, Peligro, Vulnerabilidad, Riesgo, Laharz, Modelo de elevación digital i Agradecimientos Quisiera agradecer y dedicar este trabajo en primer lugar a mi familia y amigos, por todo su apoyo en estos años de estudio. En particular a mis padres por darme una excelente crianza y apoyarme incondicionalmente hasta el día de hoy, gran parte de lo que soy es gracias a ellos. Agradezco especialmente a Fernanda, no tan solo por su amor, sino que también por ser mi compañera e inspiradora, y brindarme fuerzas y energías en momentos en las que más las necesitaba. Doy las gracias también a mi profesor guía, Luis Lara, por creer en mí y darme la oportunidad de realizar este trabajo, a Gabriel Orozco, por sus valiosos aportes y gratas discusiones en torno a este estudio, y a Rodrigo Calderón por su ayuda terreno y en el desarrollo de la temática de la vulnerabilidad. Finalmente agradezco a todos los funcionarios de la Universidad de Chile y de Sernageomin que se cruzaron en mi camino, desde los profesores hasta los ayudantes de terreno y conductores, por su aporte en el cumplimiento de mi meta profesional y por brindarme gratos ambientes de estudio y trabajo. ii Tabla de contenido 1. INTRODUCCIÓN ....................................................................................................... 1 1.1. Formulación del estudio propuesto ..................................................................... 1 1.2. Objetivos ............................................................................................................. 5 1.2.1. Objetivos generales ...................................................................................... 5 1.2.2. Objetivos específicos .................................................................................... 6 1.3. Hipótesis de trabajo............................................................................................. 6 1.4. Metodologías ....................................................................................................... 7 1.4.1. Trabajo de gabinete previo a terreno ............................................................ 7 1.4.2. Trabajo de terreno ........................................................................................ 7 1.4.3. Trabajo de gabinete posterior al terreno ....................................................... 7 1.4.4. Cartografía de vulnerabilidad y riesgo .......................................................... 8 1.4.5. Herramientas metodológicas ........................................................................ 8 1.5. Ubicación y vías de acceso ............................................................................... 13 1.6. Fisiografía ......................................................................................................... 14 2. MARCO GEOLÓGICO E HISTORIA ERUPTIVA .................................................... 16 2.1. Trabajos anteriores ........................................................................................... 16 2.2. Basamento de los volcanes Pleistoceno – Holoceno ........................................ 17 2.2.1. Rocas Estratificadas ................................................................................... 17 2.2.2. Rocas Plutónicas ........................................................................................ 19 2.3. Geología del volcán Villarrica ............................................................................ 19 2.3.1. Unidades geológicas .................................................................................. 21 2.3.2. Centros eruptivos adventicios (Holoceno Tardío) ....................................... 26 2.4. Depósitos sedimentarios del Pleistoceno – Holoceno ....................................... 26 2.5. Estructuras ........................................................................................................ 26 2.6. Registro histórico de la actividad eruptiva del volcán Villarrica ......................... 27 3. GEOMORFOLOGÍA E HIDROLOGÍA DE LOS CAUCES ........................................ 34 3.1. Río Turbio ......................................................................................................... 38 3.2. Río Pedregoso .................................................................................................. 43 3.3. Zanjón Seco ...................................................................................................... 47 iii 4. ESCENARIOS ERUPTIVOS Y SUS PROBABILIDADES ........................................ 50 4.1. Definición de escenarios eruptivos .................................................................... 50 4.1.1. Escenario 1: Erupción hawaiana – estromboliana moderada (IEV = 1) ...... 53 4.1.2. Escenario 2: Erupción estromboliana (IEV = 2) .......................................... 54 4.1.3. Escenario 3: Erupción estromboliana vigorosa – vulcaniana (IEV = 3) ...... 55 4.1.4. Escenario 4: Erupción vulcaniana – pliniana (IEV ≥ 4) ............................... 56 4.2. Análisis estadístico y probabilidad de ocurrencia de los escenarios eruptivos .. 58 4.2.1. Proceso de Poisson .................................................................................... 60 4.2.2. Probabilidad escenario 1 ............................................................................ 61 4.2.3. Probabilidad escenario 2 ............................................................................ 65 4.2.4. Probabilidad Escenario 3 ............................................................................ 69 4.2.5. Probabilidad Escenario 4 ............................................................................ 70 4.2.6. Análisis Global ............................................................................................ 72 4.3. Volúmenes de flujos laháricos para cada escenario eruptivo ............................ 76 4.3.1. Antecedentes previos ................................................................................. 76 4.3.2. Escenario 1 (IEV = 1).................................................................................. 77 4.3.3. Escenario 2 (IEV = 2).................................................................................. 81 4.3.4. Escenario 3 (IEV = 3).................................................................................. 85 4.3.5. Escenario 4 (IEV ≥ 4) .................................................................................. 91 5. CARTOGRAFÍA Y VALORACIÓN DEL PELIGRO DE INUNDACIÓN POR LAHARES....................................................................................................................... 93 5.1. Modelación computacional ...............................................................................
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