villarrica guia.cdr

4. Glaciology
Villarrica 3 is characterised by the formation of the small 450 m-high summit cone
within the youngest caldera at 2,400 m a.s.l., constituted by lava flows that have
almost covered its rim. The recent cone (Holocene, <3,700 B.P.) reaches an altitude of
2,847 m asl and consists of a sequence of lava flows with interbedded pyroclastic flow,
fallout and surge deposits (mainly basaltic to basaltic andesite in composition (50.554.5% SiO2), as well as lahar deposits. The sequence includes historic lava flows and
lahars (since 1558 A.D. up to the penultimate eruption in 1984). The last eruption in
2000 did not generate lahars nor lava flows.
1. Introduction
Volcán Villarrica (Figure 1) is located in the modern Southern Volcanic Zone (SVZ) of
the Chilean Andes at 39°30’S, being one of the most active in Chile in historical times
(Petit-Breuilh and Lobato, 1994). It forms a NW-SE volcanic chain together with the
Pleistocene-Holocene Quetrupillán and Lanín stratovolcanoes which is oblique to the
recent volcanic arc and main “Liquiñe-Ofqui Fault Zone” (LOFZ; Figure 2; Hickey et al.,
1989; Cembrano, 1990; Cembrano et al., 1992; Cembrano and Moreno, 1994; López
Escobar et al., 1995; Cembrano et al., 2000). The Middle?-Late Pleistocene to Historic
compound Villarrica stratovolcano and its products cover an area of more than 700
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km (Moreno, 1993 and 2000), being characterised by a conical shape with a 200 m
diameter open crater and small lava lake showing weak strombolian activity
(Witteretal, 2004). Its altitude reaches 2,847 m a.s.l. According to morphostructural
and stratigraphic criteria, Volcán Villarrica edifice has been divided into three evolution
stages which are described below.
During the Late Glacial Maximum (LGM), lobule type glaciers reached 210 m asl at the
lower end of Lago Villarrica and Lago Calafquén (Laugenie, 1971), where formed
several coalescent moraine arcs still visible (also visible are sandurs, terraces, ablation
moraines located down stream from the main arcs and the ice margin contact at the
lake shore, among other geomorphological features), which were probably abandoned
between 13,840 and 14,200 years B.P. (Clayton et al., 1997; Moreno & Clavero, 2006).
Very few Little Ice Age (LIA) deposits have been detected near the present lower end
of the glaciers in the surroundings of Volcán Villarrica, however, there are a couple of
valleys (Pichillancahue, and Palguin), where arrow style LIA moraines are still visible. At
present, the ice cap at Volcán Villarrica is reaching a minimum altitude of 1,750 m asl
at Glaciar Pichillancahue, Palguin valley.
Parasitic cones
More than 30 pyroclastic cones, and their associated lava flows, basaltic andesite to
andesite in composition (52 – 56% SiO2), have been erupted through the flanks of
Volcán Villarrica (mainly through Villarrica 1 edifice). These parasite centres form two
clusters: Los Nevados and Chaillupén volcanic groups, located on the northeastern and
southern flanks of Volcán Villarrica, respectively.
Glaciers and volcano interactions
There is a close interaction between volcanism and glaciers. For Volcán Villarrica, it is
recognised a highly explosive event soon after the ice started to retreat at the end of
the Last Glaciation (Naranjo and Moreno, 1991; Clavero, 1996) presumably due to an
“unloading” effect (Clavero, 1996). The explanation of this event, could be related to
the effects of deglaciation, that can produce crustal rebound because of isostatic
equilibrium restoration (i.e. Ivins and James, 1999; Ivins and others, 2000; Clague and
James, 2001; Crucifix and others, 2001). The unloading effect produces a stress relief
on the volcano magma chamber, helping magmas to reach the surface and eventually
erupt (i.e. Finn and others, 1995; Maclennan and others, 2002). At the southern shore
of Volcán Villarrica, there are several indications of an uplift of at least 60 m (Clavero,
1996) which is likely to be a response to the unloading effect of the disappearance of a
large mass of ice in the area.
Historical eruptive activity
Volcán Villarrica is Chile’s most active eruptive centre, with 59 documented eruptions
since 1558, when the first Spanish conquerors arrived to southern Chile. However,
from 31 well-documented eruptions, 8 occurred in December and 23 between spring
and summer. This suggests Villarrica volcano has a strong seasonal modulation present
in the eruptions. Historical eruptive activity has been essentially effusive with few
explosive eruptions (i.e. 1948-49 eruption). This effusive activity has produced several
lava flows, both pahoehoe and ‘aa’ type, with some associated scoria fallout deposits,
which have been directed towards the East and Southeast. The effusion of high
temperature (ca.1,100°-1,250°C) lava flows over an ice-covered volcano has generated
numerous lahars, which have traveled down the main valleys surrounding the volcano.
Figure 1. Volcán Villarrica and debris covered glacier (Photo, Camilo Rada).
2. Volcanic geology
3. Volcanic hazards associated to Volcán Villarrica
Villarrica Units
Although most of the historic eruptions have been mainly effusive, the permanent
glacier that covers the volcano, together with the seasonal snow-cap, generates a very
important volcanic hazard to its surroundings. Historical eruptions have produced lava
flows, lahars and the ejection of pyroclastic material. Hence, the main hazards
expected from future eruptions of this volcano are those that derive directly from lava
flows and tephra fallout, together with those induced by them, such as lahars and river
flooding. There is an extensive description of these hazards, in the Volcanic Hazards
Map of Volcán Villarrica published by Chilean Geological Survey (Moreno, 2000).
The older unit (Villarrica 1) consists of a 500 m thick sequence of basaltic to andesitic
lava flows, volcanic breccias, ignimbritic tuffs and agglomerates (Moreno and Clavero,
2006), being characterised by the formation of the main stratovolcano 3 km southeast
of modern cone (Gaytán et al., 2005). Moreno and Clavero (2006) suggested two subunits, one pre-last glaciation (>90,000 B.P., with Ar-Ar dates from 600 to 90 ka) and
another intraglacial (between 90,000 and 14,000 B.P.). The caldera collapse (ca. 100
ka; Clavero and Moreno, 2004) would represent the break in the early evolution of
Volcán Villarrica at the beginning of the Last Glaciation (Llanquihue).
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Villarrica 2 is considered the unit after the large Licán ignimbrite (~ 10 km ), which is
responsible for the formation of a nested caldera stratovolcano, mainly with lava flow
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eruptions, in the northwestern side of the wide caldera. According to C ages, its
formation begun probably between 13,500 and 11,000 (Late Pleistocene) and ended
with another large eruption ~3,700 (Holocene) that originated the Pucón ignimbrite (~
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5 km ) which is associated to the smaller summit caldera formation. This stratocone
consists mostly of a lava flow sequence interbedded with pyroclastic flows, fallout
tephra, laharic and surge deposits, mainly of basaltic to andesitic in composition (502
57% SiO2), covering an area over 2,000 km around the volcano.
Figure 2. Geological map of Volcán Villarrica (Moreno and Clavero, 2006).
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For instance, lava flows may virtually affect almost all around the volcano. According to
their transport, they would travel down the main valleys and spread over wider areas
at lowlands and lake shores. Lahars hazard varies according to the time of year and the
thickness of the seasonal snow cover. In the December 1971 eruption, the lahars that
descended along the river beds of Ríos Turbio and Correntoso, reached an estimated
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volume of 20 x 10 m3. Tephra fallouts should affect areas located mainly on the
eastern-southeastern side of the volcano. Although there are no important human
settlements towards the East, if a highly explosive eruption occurs, the tephra fallout
deposits could reach more populated areas further to the East, in Argentina.
Pyroclastic flows are uncommon, but if they occur, they can be extremely destructive
due to its widespread distribution. Moreover, it is important to say that there are no
evidences that the explosive phase of Volcán Villarrica has finished yet.
Glaciar Pichillancahue-Turbio
Volcán Villarrica is at present covered by a glacier of 30.3 km2 (Rivera et al., 2006). The
ice mass is mainly distributed towards the south and east side of the volcano, where
the main glacier basin (Glaciar Pichillancahue-Turbio) of a size of 17.3 km2 is formed.
The ELA is approximately at 2,000 m (in 2005) (Rivera et al., 2006).
The glacier shows an accelerated retreat, mainly due to an increase of air temperature
and decreases of precipitation (Rivera et al., 2008) like most other glaciers in the
region (Brock et al., 2007). The glacier area loss accounts 25% from 1961 to 2003, as
was detected by the analysis of satellite imagery and photogrammetric techniques
(Figure 3). The frontal variations and present extent of Villarrica’s glaciers is shown in
Figure 4.
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The ice-elevation changes determined by subtracting topographic datasets (IGM DEM
from 1961 and AirSAR C DEM from 2004) yielded at the lower parts of the glacier a
rate of -0.81 ± 0.45 ma –1 , confirming the imbalance of the glacier with present climate
conditions (Rivera et al., 2006).
Finn C., Bell R., Blankenship D. and Behrendt J. 1995. The relation of crustal
structure, warm mantle, and ice sheets to Cenozoic volcanism in West Antarctica.
Abstracts of the VII International Symposium on Antarctic Earth Sciences.
González O. 1972. Distribución del volcanismo activo de Chile y la reciente erupción
del volcán Villarrica. Instituto Geográfico Militar, Primer Symposium Cartográfico
Nacional, Santiago, Chile.
Hickey-Vargas R., Moreno H., López L. and Frey F. 1989. Geochemical variations in
Andean basaltic and silicic lavas from the Villarrica-Lanín volcanic chain (39.5°S): an
evaluation of source heterogeneity, fractional crystallization and crustal
assimilation. Contributions to Mineralogy and Petrology 103, 3: 361-386.
Hickey-Vargas R., Sun M., López-Escobar L., Moreno H., Reagan M.K., Morris J.D.
and Ryan JG. 2002. Multiple subduction components in the mantle wedge:
Evidence from eruptive centres in the Central Southern volcanic zone, Chile.
Geology,Vol. 30, no. 3, p.199-202.
Several RES profiles measured since 2003 have allowed to obtain the ice thicknesses of
the glacier (Casassa et al., 2004; Rivera et al., 2006). These profiles surveyed both in
the ash/debris-covered area and the snow-covered surfaces, from the margins of the
glacier up to 2,436 m a.s.l., yielded a mean thickness of 75 ± 4 m, the error being the
mean difference between 663 crossing points (Rivera et al., 2006). Internal layers
detected from RES profiles showed the boundary between snow and ash/debris
covered ice, consisting of pyroclastic deposits originating from the volcano, being
advected by ice flow and emerging on the ablation area of the glacier (Figure 5). These
deposits are probably related to the large Pucón Ignimbrite eruption that occurred at
3,700 BP (Clavero and Moreno, 2004), as evidenced by its characteristic juvenile
material, formed by phenocrysts-rich basaltic-andesite cauliform and breadcrusted
bombs.
Ivins E., Raymond C. and James T. 2000. The influence of 5000 year-old and
younger glacial mass variability on present-day crustal rebound in the Antarctic
Peninsula. Earth, Planets, and Space 52: 1023-1029.
Figure 6. AWS at Volcán Villarrica used for the energy balance programme (Photo, Camilo Rada).
References
Figure 5. Topographic profile showing surface and subglacial topography of Glaciar Pichillancahue
of Volcán Villarrica. In the middle is the radar non-migrated corresponding profile with subglacial
returns in white. At the bottom are Bed Power Reflection (BRP) values obtained along this profile.
The arrow indicates appearance of ash/debris covered layer on top of the glacier. (Rivera et al.,
2006). Location of A-A´ profile in Figure 4.
Credits
Jorge Clavero, PhD., Geologist
Andrés Rivera, PhD., Glaciologist
Claudio Bravo, Geographer
Martina Barandun, Bachelor in Geography
FONDECYT 1090387
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Tephra-covered glaciers are thought to be less sensitive to atmospheric temperature
changes than ‘clean’ glaciers. In a possible future warmed climate, the melt of the
winter snow cover in the ablation season would be accelerated and melt of any bare
snow or ice surface would be increased (Brock et al., 2007). A climate warming would
affect the winter mass balance since melt would most likely be extended to the top of
the accumulation zone. The magnitude and frequency of winter melt events would be
more likely, higher (Brock et al., 2007).
Laugenie C. 1971. Elementos de la cronología glaciar de los Andes chilenos
meridionales. Cuadernos Geográficos del Sur 1: 7 – 20.
Casassa, G., Acuña C., Zamora R., Schliermann E. and Rivera, A. 2004. Ice thickness
and glaciar retreat at Villarrica Volcano. In: LARA L. & CLAVERO, J. (Eds.). Villarrica
Volcano (39.5ºS), Southern Andes, Chile. SERNAGEOMIN, Boletín 61, 53-60.
Maclennan J., Jull M., McKenzie D., Slater, L. and K. Grönvold. 2002. The link
between volcanism and deglaciation in Iceland. Geochemistry, Geophysics,
Geosystems 3(11), 1062, DOI: 10.1029/2001GC00282.
Cembrano J. 1990. Geología del Batolito Norpatagónico y de las rocas
metamórficas de su margen occidental: 41º50’S-42º10’S. Unpublished thesis,
University of Chile.
Moreno H. 1993. Volcán Villarrica: Geología y Evaluación del Riesgo Volcánico,
regiones IXª y Xª, 39°25’S. Unpublished Fondecyt report, 112p.*
Cembrano J., Beck M., Burmester R., Rojas C., García A. and Hervé F. 1992.
Paleomagnetism of Lower Cretaceous rocks from east of the Liquiñe-Ofqui fault
zone, southern Chile: evidence of small in-situ clockwise rotations. Earth and
Planetary Science Letters 113: 539-551.
Moreno H. 2000. Mapa de Peligros Volcánicos del Volcán Villarrica. Documentos de
Trabajo No. 17, Servicio Nacional de Geología y Minería, escala 1:75.000.
Moreno H. and Clavero J. 2006. Mapa geológico del volcán Villarrica. Serie Geología
Básica, No., p. Servicio Nacional de Geología y Minería.
Cembrano J. and Moreno H. 1994. Geometría y naturaleza contrastante del
volcanismo entre los 38ºS y 46ºS: ¿Dominios compresionales y tensionales en un
régimen transcurrente? Abstracts 7th Chilean Geological Congress, Concepción, vol
I, p.240-244.
Overall, the glacier is experiencing both thinning and area reduction, in spite of
presenting a thick layer of ash and debris (thicker than 1m in places) covering most of
the ablation area. In some places where the glacier is more crevassed, backwasting
seems to be an important process on steep ice walls. Apart from the possible volcanic
component, which is affecting Glaciar Pichillancahue, the main glacier variations are
driven by climate change or decadal atmosphere/ocean oscillations (i.e. the 1976
shift). However, not all changes are a direct response to warmer/drier conditions, as
an important role is played by feedbacks triggered by climatic changes. Among these
feedbacks, the ice surface elevation and glacier length responses are the most
important (Rivera et al., 2006).
Francisca Bown, MSc, Geographer
Ivins E. and James T. 1999. Simple models for Late Holocene and present-day
Patagonian glacier fluctuation and predictions of a geodetically detectable isostatic
response. Geophysical Journal International 138: 601-624.
Brock B., Rivera A., Casassa G., Bown F. and Acuña C. 2007. The surface energy
balance of an active ice – covered volcano: Villarrica volcano, southern Chile.
Annals of Glaciology 45: 104 – 114.
In many surveyed areas, the subglacial topography was not visible or was confused by
internal layers, requiring new and denser data to detect deeper ice. One of these areas
is illustrated in Figure 5 where the subglacial topography is interrupted. These
features were visible in all the records obtained from this sector of the glacier,
suggesting that large crevasses obscure the bedrock returns. These crevasses could be
related to a break or a large crater structure in the subglacial topography. The mean
ice thickness obtained in Volcán Villarrica represents areas where signals were
sufficiently clear to be distinguished from internal layers.
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Crucifix M., Loutre M., Lambeck K. and Berger, A. 2001. Effect of isostatic rebound
on ice volume variations during the last 200 yr. Earth and Planetary Science Letters
184:623-633.
The influence of the volcanic activity on the overlaying glaciers shows two contrasting
effects. On one hand a geothermal flux at the glacier’s base reinforces melt. On the
other hand, where thick enough isolating debris and ash layers are present, the ice is
protected from melting, reducing ablation and having a positive effect on the mass
balance (Rivera et al., 2006; Brock et al., 2007). These findings were observed at
Automatic Weather Stations (AWS) installed on the glacier together with mass balance
measurements carried out on the glacier (Figure 6). Energy balance monitoring (Brock
et al., 2007) has been combined to Global Positioning System (GPS) and Radio Echo
Sounding (RES) measurements since 2004 (Rivera et al., 2006).
Figure 4. Glacier variations, 1961-2009, at Volcán Villarrica. The yellow dot shows the summer AWS
location. The star shows the location of the camera and the GPS station. (Updated from Rivera et al,
2008). A-A´ RES profile showed in Figure 5.
Figure 3. Photographic camera (red arrow) setup for mapping glacier dynamics,
albedo, and snow deposition (Rivera et al., 2008) (Photo, Camilo Rada).
Naranjo J. and Moreno H. 1991. Actividad explosiva postglacial en el volcán Llaima,
Andes del Sur. Revista Geológica de Chile, 18 (1): 69-80.
Cembrano J., Schermer E., Lavenu A. and Sanhueza A. 2000. Contrasting nature of
deformation along an intra-arc shear zone, the Liquiñe-Ofqui fault zone, southern
Chilean Andes. Tectonophysics,Vol. 319, p. 129-149.
Rivera A., Bown F., Mella R., Wendt J., Casassa G., Acuña C., Rignot E., Clavero J.
and Brock B. 2006. Ice volumetric changes on active volcanoes in Southern Chile.
Annals of Glaciology 43: 111 - 122.
Clague J. and James T. 2001.History and isostatic effects of the last ice sheets in
southern British Columbia. Quaternary Science Reviews. Clapperton C (1993)
Quaternary Geology and Geomorphology of South America, Elsevier, Amsterdam,
466p.
Rivera, A., Corripio J., Brock B., Clavero J. and Wendt J.. 2008. Monitoring icecapped active Volcán Villarrica, southern Chile, using terrestrial photography with
automatic weather stations and global positioning system. Journal of Glaciology 54:
920 – 930.
Clavero J. 1996. Ignimbritas andesítico-basálticas del Volcán Villarrica, Andes del
Sur (39°30’S). Unpublished MSc thesis, University of Chile, 112p.*
Witter J., Kress V., Delmelle P. and Stix J. 2004. Volatile degassing, petrology, and
magma dynamics of the Villarrica lava lake,Southern Chile. Journal of Volcanology
and Geothermal Research 134: 303-337.
Clavero J. and Moreno H. 2004. Evolution of Villarrica volcano. In Lara and Clavero
(eds.) Villarrica volcano, Southern Andes. Boletín No. 61 Servicio Nacional de
Geología y Minería, Chile.
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Clayton J., Clapperton C. and Antinao-Rojas J. 1997. Las glaciaciones
pleistocénicas en la cuenca del Lago Villarrica, Andes del Sur. Actas del VIII
Congreso Geológico Chileno, Antofagasta, Vol 1: 307 – 311.
(*) Unpublished Document available at the Library of the Servicio Nacional de Geología
Minería, Avenida Santa María 0104, Providencia,Santiago. Chile.
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Stops
Stop 1.- Outskirts of Coñaripe
Coñaripe is a small touristic town located on the eastern shore of Lago Calafquén. In March 1964,
the northern part of the town was completely destroyed by a lahar originated at Volcán Villarrica,
killing more than 20 people. We will observe the few remaining trees of the old town and the
marks left by the ca. 2 m high wave which reached the town, leaving half of the town into the lake.
After this disaster, the area is once again urbanized and several touristic facilities have been built.
Stop 2.- Chaillupén River
We will look at one of the lavas which were generated during the 1971 eruption. This is an Aa-type
andesitic lava, which also generated a lahar that reached Lago Calafquén triggering a small
tsunami. The lava took several days for reaching this area, after moving for ca. 12 km from its
source.
Stop 3.- Outskirts of Licán Ray
We will look at the distal deposits of the largest Postglacial explosive eruption of Volcán Villarrica:
the Licán Ignimbrite. In this area (at ca.20 km from the western caldera rim) the deposit sits on top
of morainic deposits of the Last Glaciation (Llanquihue Drift). The deposit is more than 8 m thick
and shows, at least, 3 flow units. Its base shows local surge deposits, produced by the irregular
topography on which it traveled and deposited. The upper flow units are generally massive,
although some internal structures can be observed (bomb trends, parallel lamination, etc.). The
contact with the morainic deposits shows sometimes a reddish color as well as carbonized wood
and gas segregation pipes, suggesting a hot emplacement on top of still humid glacial deposits.
Stop 4.- Willylafquen area-Ski center road
Pucón Ignimbrite (3.7 ka) is the second large mafic pyroclastic flow at the top of Villarrica 2 unit,
which produced a summit collapse of the stratovolcano generating caldera at 2,400 m a.s.l.
Compared with the Licán ignimbrite, this deposit has much more lithics, thus it was much slower
and in the Zanjón Seco valley, the flow was extremely canalized. In this place, the deposit consists
roughly in four flow units, which individually show little structures, although some parallel bedding
and lenses containing big scoriaceous bombs and/or lithics, together with carbonized trees usually
imbricated along the flow direction. From base to top,the different flow units contain different
amounts of juvenile and lithic material. At lower levels, it consists mainly of scoriaceous bombs (up
to 60 cm in diameter) and lapilli, with plenty charred wood. A second horizon has scoria, lithics
and an indurate ash matrix with carbonized trees. Then a third thinner hard layer consists of lithic
fragments and sand,followed by a 4.5 m thick upper horizon with three lithic rich facies, the
middle one with big angular fragments up to 35 cm in diameter.
Stop 5.- Pucón viewpoint
In this place there is a magnificent view of Villarrica volcano (Units 2 and 3), if not cloudy. The
roadcut shows a lateral moraine of the Estero Zanjón Seco, which belongs to the last Glaciation
(Llanquihue Drift), covered by almost the whole Postglacial pyroclastic sequence of Volcán
Villarrica explosive record. The large Licán ignimbrite is missing here but outcrops are visible some
hundredth of meters toward south along the road. The first ignimbrite layers over the moraine are
quite weathered, and the higher one that underlies the noticeable pumice fall deposit from
Mocho-Choshuenco volcano, has a 14C age of 9.7 ka. On top of it we can observe several
weathered pyroclastic flow deposits that underlie a conspicuous but thin grey surge deposit
equivalent to the Pucón event upper facies (3.7 ka). The surge layer is followed by two significant
mafic air-fall tephra, covered by younger pyroclastic flow deposits on the top, all of them belong
to Villarrica unit 3.
View from the south to the remnants of Coñaripe village,
after the March 1964 lahar which killed tens of people.
1971 lava flow at Chaillupén valley.
From this place looking north and northeast, toward the Estero Zanjón Seco, it can be observed
the Postglacial fast filling of ignimbrites, lava flows and laharic deposits that came from the
volcano. Thus, when the Licán ignimbrite eruption took place at the Postglacial beginning, the
Estero Zanjón Seco valley was much deeper than today. Therefore, most of it was confined to it,
although some surge facies overflowed as seen upwards in the road cut. Far down the Pucón town
can be seen, located on an evident hazardous area.
Willylafquén. Channel juvenile-rich facies of the Pucón
Ignimbrite deposit, showing several flow units.
1949 Volcán Villarrica eruption.