Nevados de Chillán 

 


 

The Nevados de Chillán complex (36º 51’ 48’’ S - 71º 22’ 36’’ W; 3212 m a.s.l) is a composite stratovolcano with polygenic characteristics, composed by a number of volcanic edifices, lava domes, pyroclastic cones andparasitic cones (Déruelle, 1974; Déruelle, 1977; Dixon et al., 1999; Naranjo and Lara, 2004, Mee et al., 2006).The complex is composed by two volcanic edifices (González-Ferrán, 1995), the so called Nevados de Chillán orCerro Blanco to the NW (3212 m asl) and Las Termas/Volcan Chillán/Volcan Arrau subcomplex to the SE (3186m asl), both separated by the Portezuelo Los Baños (Figure 2). Cerro Blanco preferentially emits basalticandesiteto andesits with the last event in 1861-65 at the Santa Gertrudis cone (Philippi, 1862).

 

Las Termas complex erupts more silicic lavas, andesites, dacites and low-Si rhyolites, being the last longeruptive event between 1973-86, when a new lava cone of 100-150 m was built, named Volcán Arrau, yielding amaximum height of 3206 m asl in 1983, almost 20 m higher than nearby Volcán Nuevo (Naranjo and Lara,2004). The last small explosive event occurred in late 2003 (Naranjo and Lara, 2004), with the emission of a lowaltitudeeruptive column that lasted less than a few hours.

 

The historical occurrence of volcanic activity of theNevados de Chillán complex has been compiled amongothers by Petit-Breuilh (1995), being one of the mostactive volcanoes of the Southern Volcanic Zone (SVZ).The complex is partially covered by glaciers which werefirstly described by Philippi (1862), which have shrunk in2004 to an area of only 6 km2 of ice distributed in 25small ice bodies (Zenteno et al., 2004). Among theseglaciers, there are several ash/debris covered ice bodiesand few bare ice glaciers. No studies of these glaciershave been accomplished up to date, but one snow route,frequently measured by DGA at Volcán Chillán, wasincorporated into a recent analysis by Masiokas et al.(2006). The vicinity of the Termas de Chillán resort centreprovides logistic facilities for a more reliable winter andsummer access to the glaciers.

 

 

Volcán Villarrica

 


 

Volcán Villarrica (Figure 3) is considered to be one of the twomost active volcanoes in the Andes. Its eruptive activity inhistorical times is mainly characterized by mild strombolianactivity (González-Ferrán, 1995; Lara, 2004), permanentdegassing and periodic explosions, with the lava lake remainingat a high level (90-180 m below surface) at least since 1984 andvery sensitive to the magmatic conduit activity (Calder et al.,2004; Witter et al., 2004). Concentrations of acid gasesmeasured at the summit of the crater have been recognizedeven as a hazard to climbers ascending the volcano, who maybe exposed to concentrations above limits defined by the U.S.National Institute of Occupational Safety and Health (Witter andDelmelle, 2004). Its historical eruptive activity indicates (Petit-Breuilh and Lobato, 1994; Lara, 2004) low frequency of largeexplosive eruptions (Volcanic Explosivity Index, VEI between 3and 4) however more than 500 eruptive events have beendocumented since 1558 (Petit-Breuihl and Lobato, 1994), andtens of more explosive eruptions (VEI 3 to 6) are recorded inpre-historical times, including two large ignimbrite-formingeruptions in the Late Pleistocene and Holocene (13.7 and 3.7ka BP; e.g. Moreno and Clavero, 2006).

 

The latest most violent eruption in recent times took place in 1971-72 when lava flows were generated, as wellas 30 to 40 km hr-1 laharic flows descending towards Lagos Villarrica and Calafquén (Naranjo and Moreno,2004). During the first stages of the 1971-1972 eruptive cycle, lava fountaining pouring out from a NNE fissureon the upper flanks of the volcano generated rapid melting of the glacier cap (González-Ferrán, 1995; Naranjoand Moreno, 2004), both towards the northern flank and towards the southwestern flank of the edifice, wherethe main lava flows were distributed (Moreno and Clavero, 2006). Lahars produced by eruptions of VolcánVillarrica in 1948-1949, 1963-1964, and 1971-1972 have resulted in the death of more than 75 people (Stern,2004), being considered the main hazard factor of the volcano (Moreno, 2000). The volcano is covered by aglacier of 30.3 km2 (volume in 2005; Rivera et al., 2006A), mainly distributed toward the south and east wherethe main glacier basin (Glaciar Pichillancahue-Turbio, 17.3 km2) composed of partially ash/debris-covered iceis located. This glacier partially infills a volcanic caldera depression (Clavero and Moreno, 2004) associated totwo partial collapses of ancestral edifices. The energy balance of this glacier has been monitored since 2003(Brock et al., 2007), and Global Positioning System (GPS) as well as Radio Echo Sounding (RES), and otherglaciological measurements have been carried out between 2005 and 2007 (Rivera et al., in press).

 

 

Volcán Hudson

 


 

Volcán Hudson is an active stratovolcano with a 10 km diameter caldera (Figure 4) at the southern tip of theSouthern Volcanic Zone (SVZ) at 45º54’S, 72º58’W, 1905 m asl (Naranjo et al., 1993; Gutiérrez et al., 2005),only recognized as an active volcano in 1970 (Fuenzalida and Espinoza, 1974) due to its remoteness andunpopulated location in the Aysén region. More than 10 eruptions have been detected during the Holocene.Those occurred in 3600 y BP and especially the 6700 y BP being the largest ever recorded in the SouthernAndes during that time (Stern, 1991). The Hudson caldera was thought to have been generated during one ofthese big Holocene eruptions (Naranjo and Stern, 1998), however Orihashi et al. (2004) proposed that it wasformed by multiple collapse events. In recent historical times a subplinian to plinian eruption with two eruptivecycles took place in August and September of 1971, characterized by a maximum VEI of 4 (Naranjo et al.,1993).

 

The eruptive plume generated by the 1971 event was composed by gasses and ashes, that reached up to12,000 m, distributing pyroclastic material toward the East in Chile and Argentina. Several lahars descendedthrough the Huemules valley (Fuenzalida, 1976).

 

In 1991, the volcano experienced the second largest Plinian eruption in Chilean historical times with a VEI of 4,which produced > 4km3 bulk volume of tephra, affecting an area of more than 150,000 km2 in Chile andArgentina. Several lahar flows were reported at Río Huemules without casualties, however, the economic andsocial impacts were severe (Naranjo et al., 1993).

 

Fuenzalida (1976) estimated that 80% of the ice withinthe caldera was melted during the 1971 eruption,however by the end of the 1980s almost 90% of calderawas ice-covered (~ 65 km2). The 1991 eruption meltedan approximated area of 15 km2. The equilibrium linealtitude (ELA) of Volcán Hudson is located at 1300 masl and the precipitations in this region are higher than 4m per year, therefore ice recovery is an important issuewithin the caldera. The total ice area within the calderain 2002 yielded a value of 51 km2. Assuming aconservative mean ice thickness of 100 m, the totalvolume of ice storage on top the volcano would be 5km3 (Rivera et al., 2006B). This figure is the double ofthe previous estimations by Naranjo and Stern (1998).

 

The limited data available for this volcano is a challengefor this project, where any modelling task effort willrequire a lot of basic surveying and mapping. Thesemeasurements will be carried out during airbornecampaigns that are going to be validated with groundsurveys, where we expect to improve our knowledgefrom this remote place.