GeoSur2013 25-27 November 2013 – Viña del Mar (Chile)
Acknowledgements We thank Mighty River Power (New Zealand) and MRP Geotermia Chile Ltda for granting permission to publish this work. We also acknowledge the support given by GeoGlobal Energy during the execution of this project.
REFERENCES • Angermann, D., Klotz, J., Reigber, Ch., 1999. Space-geodetic estimation of the Nazca–South America Euler vector. Earth and Planetary Science Letters 171 (3), 329–334. • Barrios, L.; Hernández, B.; Quezada, A.; Pullinger, C. 2011. Geological hazards and geotechnical aspects in geothermal areas, the El Salvador experience. Presented at “Short Course on Geothermal Drilling, Resource Development and Power Plants”, organized by UNU-GTP and LaGeo, in Santa Tecla, El Salvador, January 16-22, 2011. • Cembrano, J.; Hervé, F.; Lavenu, A. 1996. The Liquiñe-Ofqui fault zone: a long-lived intra-arc fault system in southern Chile. Tectonophysics, 259, 55-66. • Polanco, E. 1998. Volcanismo explosivo postglacial en la cuenca del Alto Biobio, Andes del Sur (37°45’-38°30’). Memoria para optar al título de Geólogo. Universidad de Chile. • Stimac, J.; Lohmar, S.; Colvin, A.; Stacey, R.; Wilmarth, M.; Melosh, G.; Iriarte, S.; González, A.; Mandeno, E. 2013. 2012 Tolhuaca Resource Assessment. GeoGlobal Energy internal report, 182 p. • Vergara, C.; Lara, L.; Sellés, D. 2012. Complejo Volcánico Lonquimay (38,2°S): Características geoquímicas atípicas en el contexto de la Zona Volcánica Sur. P. 513-515, XIII Congreso Geológico Chileno, Antofagasta. • Wardman, J.B.; Wilson, T.M.; Bodger, P.S.; Cole, J.W.; Stewart, C. 2012. Potential impacts from tephra fall to electric power systems: a review and mitigation strategies. Bulletin of Volcanology, DOI 10.1007/s00445-012-0664-3.
Apagado Volcano scoria cone (Southern Andes, 42°S): 2-23 a basaltic Plinian eruption at 2,480 yB.P.
Mauricio Mella B.
Servicio Nacional de Geología y Minería, Oficina Técnica Puerto Varas, Puerto Varas, Chile. * Presenting Author’s email: [email protected]
Abstract Basaltic eruptions are typically characterized by Strombolian and Hawaiian eruptive styles. However, a few examples of Plinian basaltic eruptions have been documented in the world. The Ap-1 eruption from Apagado Volcano scoria cone is a bedded dark grey and orange-brown, glassy, elongated scoria deposit dispersed ESE, well-stratified, characterized by a base unit with basement lithics. The mass estimation suggests a magnitude above 5.3 with a 13 to 24 km plume height. This is the biggest Holocene eruption in the Calbuco-Chaitén segment, but in this case not related to large volcanoes (e.g. Yate or Hornopirén), instead to a small scoria cone. Thus, Apagado Volcano scoria cone becomes the principal potential ash- fall threat for Río Negro – Hornopirén towns and Ap-1 is one of the major explosive basaltic eruptions recognized in the region.
Introduction The basaltic Plinian eruptions are rare in most of the basaltic volcanoes. Basaltic eruptions are typically characterized by Strombolian and Hawaiian styles. However, a few examples of large explosive basaltic eruptions have been documented in the world: Fontana Lapilli in Nicaragua (Wehrmann et al., 2006), Etna in Italy (Coltelli et al., 1998), Tarawera eruption in New Zealand (Walker et al., 1984), Villarrica and Llaima in Chile (Moreno and Clavero, 2006; Naranjo and Moreno, 2005). This contribution reports new data on thickness and maximum particle size, as well as the magnitude and dispersion of Ap-1 eruption. The Apagado Volcano is a small scoria cone representing the Hualaihué Volcano youngest unit (Mella, 2008) and consists of basaltic to basaltic andesite lava and tephra (Mella, 2008; Watt et al., 2011).
178
001-364 GeoSuf 2013 178 11-11-2013 9:16:19 GeoSur2013 25-27 November 2013 – Viña del Mar (Chile)
Stratigraphy and distribution of Ap-1 eruption Watt et al., (2011) first recognized the Ap-1 eruption as a bedded dark grey and orange-brown, glassy, elongated scoria deposit, well-stratified on cm-scale. They proposed the Apagado Volcano as the source for Ap-1 eruption, and suggested that this deposit would represent a minor explosive eruption (
Fig. 1 - Photographs of Ap-1 deposit that outcrops about 1 km to E from the Apagado Volcano, showing contacts between different units and the presence of grey layers with basement-bearing component (arrows).
Eruptive volume, mass and magnitude Several methods are proposed for estimating volumes, mass and plume height from isopach and isopleth maps (Pyle, 1989; Fierstein and Nathenson, 1992; Bonadonna et al., 1998; Bonadonna and Costa, 2012; Bonadonna and Costa, 2013). Also, the volume of tephra fall layers characterizes the magnitude of an eruption (Pyle, 2000). The mass estimation of the Ap-1 eruption suggests a magnitude above 5.3 with a 13 to 24 km plume height (Fig. 2). The magnitude and plume height are typical of Plinian eruptions (Pyle, 2000; Bonadonna and Costa, 2013; Fig. 2). Therefore, the Ap-1 is the biggest Holocene eruption in the Hualaihué area and it is not related to the large stratovolcanoes of the region (e.g. Yate or Hornopirén). This
179
001-364 GeoSuf 2013 179 11-11-2013 9:16:20 GeoSur2013 25-27 November 2013 – Viña del Mar (Chile)
Fig. 2 - Isopach and isopleth maps of Ap-1 eruption, with Weibull fit within the Plinian style.
suggest that the Apagado Volcano scoria cone is the main threat for Río Negro – Hornopirén towns and Ap- 1 is one of the major explosive basaltic eruptions recognized in the region.
Acknowledgements This work has been funded through sectorial funds from SERNAGEOMIN. L. Lara and H. Moreno (SERNAGEOMIN) are acknowledged for reviewing of this text.
REFERENCES • Bonadonna C.; Costa, A. 2012. Estimating the volume of tephra deposits: a new simple strategy. Geology 40(5):415–418 • Bonadonna C.; Costa, A. 2013. Plume height, volume, and classification of explosive volcanic eruptions based on the Weibull function. Bulletin of Volcanology 75(8): 1-19 • Bonadonna C.; Ernst G.; Sparks R.S.J. 1998. Thickness variations and volume estimates of tephra fall deposits: the importance of particle Reynolds number. Journal of Volcanology Geothermal Resource 81(3–4):173–187. • Coltelli M.; Del Carlo P.; Vezzoli L. 1998. Discovery of a Plinian basaltic eruption of Roman age at Etna volcano, Italy. Geology 26:1095–1098 • Fierstein, J.; Nathenson, M.1992. Another look at the calculation of fallout tephra volumes: Bulletin of Volcanology 54:156–167. doi:10.1007/BF00278005. • Mella, M. Petrogenesis of the Yate Volcanic Complex (4230’S), Southern Andes, Chile. PhD Thesis, Institute of Geosciences, University of Sao Paolo, Brazil, 2008.
180
001-364 GeoSuf 2013 180 11-11-2013 9:16:22 GeoSur2013 25-27 November 2013 – Viña del Mar (Chile)
• Moreno, H.; Clavero, J., 2006. Geología del área del volcán Villarrica, Regiones de la Araucanía y de los Lagos. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geología Básica, No. 98, p.35, 1 mapa escala 1:50.000, Santiago. • Naranjo, J.A.; Moreno, H. 2005. Geología del volcán Llaima, Región de la Araucanía. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geología Básica, No.88, 33 p., 1 mapa escala 1:50.000, Santiago. • Pyle, D.M. 1989. The thickness, volume and grainsize of tephra fall deposits. Bulletin of Volcanology 51:1-15. • Pyle, D.M. 2000. Sizes of volcanic eruptions. In: Sigurdsson, H. (Ed.), Encyclopedia of Volcanoes: 463-475. Academic Press, San Diego. • Walker G.; Self S.; Wilson L. 1984. Tarawera, 1886, New Zealand—a basaltic Plinian fissure eruption. Journal of Volcanology Geothermal Resource 21:61–78 • Watt, S.; Pyle, D.; Naranjo, J.A.; Rosqvist, G.; Mella, M.; Mather, T.; Moreno, H. 2011. Holocene tephrochronology of the Hualaihue region (Andean southern volcanic zone, ~42° S), southern Chile. Quaternary International 246 (1–2):324-343 • Wehrmann H.; Bonadonna C.; Freundt A.; Houghton B.F.; Kutterolf S. 2006. Fontana Tephra: a basaltic Plinian eruption in Nicaragua. In: Rose W., Bluth G., Carr M., Ewert J., Patino L., Vallance J. (eds). Volcanic hazards in Central America. Geological Society of America, Special Paper 412: 209–224
The high social and economic impact 2013 summer debris 2-24 flow events in Central Chile and Argentina
Stella M. Moreiras*1 and Sergio A. Sepúlveda2
(1) CONICET- IANIGLA (CCT Mendoza). Av. Ruiz leal s/n Parque Gral San Martín. Mendoza. 5500. Argentina. (2) Departamento de Geología, Universidad de Chile. Plaza Ercilla 803, Santiago. * Presenting Author’s email: [email protected]
Introduction During the southern-hemisphere summer months of January and February 2013, local but very intense rainfall events caused a number of debris flows in the Andes Main and Frontal ranges of central Chile and Argentina at about 32-34º S. The flows were mainly triggered in the Maipo and Aconcagua valleys (Chile), concentrated in two distinct rainfall events, and along the Mendoza River valley (Argentina) in a more distributed manner. The flows caused serious disruption to the international road infrastructure and high impact to the population, mainly due to potable water supply cut offs to major cities. In this short paper we document the location and field observations of these events and describe their impacts to society.
Debris flows in Central Chile Two distinct rainfall events in 21st January and 8th February 2013 caused several debris flows in the Central Chile Andean valleys. In both cases the rainfall was very localized, attributed to convective cells that caused short, intense precipitations in discrete catchments, while in the few meteorological stations around the area the measured rainfall was null or negligible, with a maximum of 11 mm and 8 mm of daily precipitation in the Maipo basin for the 21st January and 8th February, respectively (DGA, 2013). Therefore, there is no information of the precise amount of rain that produced the flows. The 21st January event produced important debris flows in the Maipo valley (33.5º-33.8ºS), and some minor flows and flooding were reported in the Cachapoal valley (34ºS) causing road interruptions (Sernageomin 2013a, 2013b). The most damaging event occurred in the San Alfonso creek and other minor lateral tributaries of the Maipo and Volcán rivers in the Maipo basin (Fig. 1). According to tourists that were camping on the San Alfonso gully and field observations, the flow was rich in sandy mud and transported blocks of over 1 m. Splash marks at bridges next to the confluence with the Maipo River show that the flow reached heights of up to about 3 m, with a deposit thickness of 0.5 to 1 m. The flow would have generated at the catchment uplands, with a travel distance of up to about 9 km before reaching the Maipo river. Meanwhile, the same climatic event caused smaller debris and mudflows in at least three steep tributary creeks of the
181
001-364 GeoSuf 2013 181 11-11-2013 9:16:22