Taking the pulse of a large volcano: Mocho-Choshuenco, Chile

Taking the pulse of a large volcano: Mocho-Choshuenco, Chile

As the recent eruptions of Calbuco and Villarrica in southern Chile have shown, the long arcs of volcanoes that stretch around the world’s subduction zones have the potential to cause widespread disruption to lives and livelihoods, with little or no warning. Fortunately, neither of these eruptions has, so far, led to any reported loss of life – but the consequences  of these eruptions for the communities living within reach of the ash plumes and beyond will continue to play out for months or years into the future.


The young cone of Mocho volcano, southern Chile, which may have erupted as recently as 1937. Mocho-Choshuenco volcano is one focus of our ongoing work in the region.

We have been working in southern Chile for a few years now, helping to extend what is known about past explosive eruptions at some of the region’s most active volcanoes. In this part of Chile, the written records of past eruptions only extend back a few hundred years – at the most – so most of our work has involved digging into the geological records of the region, to try and piece together the fragmentary stories of past eruptions. This can be slow and painstaking work, both in the field and in the laboratory, but is always exciting when things start to come together.

Field sampling on Mocho-Choshuenco volcano: deposits of the ‘Enco’ eruption.

This week, Harriet Rawson has published her first major scientific paper on the volcanic eruption history of Mocho-Choshuenco over the past 18,000 years. The 18,000 year timescale spans the volcanic activity that has taken place since the end of the last ice age; and we can be fairly confident that by visiting hundreds of sites around the volcano, we have found most of the ‘major’  eruptions, and many of the ‘moderate’ explosive eruptions from this volcano over this time period. The results of Harriet’s work are summarised in the picture below – which shows the timing, composition and sizes of eruptions through time. Just for context, the March 3 eruption of Villarrica was small (10 million cubic metres of ash, or magnitude 3 on the y axis), with a composition represented by an orange colour (so a bit like the Mocho eruptions around 4,000 years ago); while the April 22 eruption of Calbuco was moderate (210 million cubic metres of ash, or magnitude 4.5 on the y axis), and a composition in the green to pale blue range (like the eruption around 2000 years ago).


The record of explosive volcanic eruptions at Mocho-Choshuenco volcano over the past 18,000 years (from Rawson et al., 2015). The x axis shows time, as ‘thousands of years before present’, based on radiocarbon dating of flecks of charcoal preseved within the deposits. The y-axis shows the ‘size’ of the eruption, in terms of the eruption magnitude, which is a logarithmic scale of erupted mass or volume of ash and pumice. The coloured curves represent the age and erupted composition of the volcanic events that have been recognised – with the ‘peak’ of the curve showing the best estimate of the eruption age, and size. The width of the curve gives an indication of the uncertainty in the timing of the eruption. The cartoon parallel to the x-axis shows how regional climate and ice cover at the volcano are thought to have changed over the same time period.

In many ways, this work is just the start of the forensic process of understanding how this particular volcano works and of the threats it might pose for the future;  but it is also a critical piece of the jigsaw in terms of understanding the pulse of the volcanic arc, and crossing the gap between the geological past, and the volcanic present.


The wonderful ‘Salto Huilo Huilo‘ in the Huilo Huilo ecological reserve, at the foot of Mocho-Choshuenco.


This work has been funded primarily by the UK Natural Environment Research Council, and represents the outcome of many years of collaborations with colleagues from the Chilean Geological Survey, SERNAGEOMIN, with field work in the region supported by numerous colleagues and assistants, and with the support of CONAF and Reserva Huilo-Huilo.


K Fontijn et al., 2014, Late Quaternary tephrostratigraphy of southern Chile and Argentina, Quaternary Science Reviews 89, 70 – 84. [Open Access]

H Rawson et al., 2015, The frequency and magnitude of post-glacial explosive eruptions at Volcan Mocho-Choshuenco, southern Chile. Journal of Volcanology and Geothermal Research, doi:10.1016/j.jvolgeores.2015.04.003 [Open Access] Datasets available on figshare.

DM Pyle, 2015, Sizes of volcanic eruptions, Chapter 13 in Sigurdsson et al., eds, Encyclopedia of Volcanoes, 2nd edition, pp 257-264. doi:10.1016/B978-0-12-385938-9.00013-4

Villarrica erupts. March 3, 2015, Chile.


Volcan Villarrica from the air in 2009.


Villarrica (Ruka Pillan in Mapudungun) is one of the most active volcanoes of southern Chile, and is a popular tourist destination in the heart of the Chilean Lake district. Villarrica has been in a continuous state of steady degassing for much of the past 30 years, since the last eruption in 1984-5, and began showing signs of increased unrest (seismicity, and visible activity in the summit crater) in February 2015. Eruptive activity at Villarrica in 1963-4 and 1971 was characterised by vigorous ‘Strombolian’ explosions from the summit – typically with short paroxysms of fire fountaining – followed by the formation of lava flows. The major hazards at Villarrica come from the lahars, which form as a result of the melting of snow and ice from the summit glacier by the intruding or erupting magma. In 1963 and 1971 the lahars that swept off the volcano caused considerable damage, and a number of fatalities in the affected areas.

At the present day, the volume of ice in the summit region is a little over 1 cubic kilometer. Any melt waters and lahars that may form as a consequence of the volcanic activity are expected to drain along any or several of the nine major lahar channels that were either active during the past eruptions of Villarrica, or have been identified from fieldwork and mapping. Recent work on the sediments from Lake Villarrica show that the transport of volcanic ash into the lake by lahars forms a very clear record of the small eruptions of the volcano that would otherwise not be preserved.

Lahar map

Map showing the nine major lahar channels (in blue) that drain off the summit of Villarrica, The area outlined in red shows the extent of the summit glacier field in Februiary 2011. The main tourist resort of Pucon, and lake Villarrica, lie to the north. In 1964, lahars caused  much damage to the village of Conaripe, to the south. Map from Rivera et al. (2015) , lahar channels from Castruccio et al. (2010).

The first Strombolian paroxysm from the 2015 eruption was reported shortly after 3 am local time on 3rd March; and this was followed by reports on social media of spontaneous evacuations from some of the communities that have been affected by lahars in the past. The Chilean agency responsible for civil protection (ONEMI, Oficina Nacional de Emergencia del Ministerio del Interior y Seguridad Pública) declared a ‘red alert‘ shortly afterwards, and SERNAGEOMIN also raised their technical ‘volcanic alert’ level to red. If the current phase of activity follows the pattern of past eruptions, there may be an extended period of elevated activity with intermittent paroxysms over the next few days to weeks.

This paroxysm just lasted a few tens of minutes, but released large puff of ash that rose to about 9 km above sea level and could be seen on geostationary weather satellites; a burp of sulphur dioxide that was visible from space, and coated the summit of Villarrica with a fresh coating of volcanic ‘spatter’.  On the volcano itself, there was clearly some melting of snow and ice, and small amounts of volcanic ash were washed down the local drainages, and into Lake Villarrica.

The footprint of the ‘hotspots’ associated with the freshly deposited ejecta can be seen in the alerts detected by University of Hawaii’s MODIS Thermal Alert System, using imagery from the MODIS sensors onboard NASA’s Terra and Aqua satellites.

MODVOLC screen shot

Screen shot of the ‘thermal alerts’ detected by the HIGP MODIS Thermal Alert System for Villarrica, on 3 March 2015.

Update – March 5th, 2015.

The eruption was over quite quickly, and although a few thousand people evacuated at the time, most returned home later that day. Flights over Villarrica by the volcano monitoring and civil protection teams on March 3rd, and subsequent days, showed that the summit vent became sealed by fresh spatter during the eruption, but signs of activity diminished very quickly. SERNAGEOMIN reported that only one monitoring station was lost during the eruption, and their current scenario is that there may be some intermittent weak Strombolian activity in the near future, which should be readily detectable on the monitoring systems. Photographs posted on social media showed only little evidence for limited damage by lahars during this first eruption; including damage to a tourist centre on the volcano slopes.

Ongoing Activity

Latest status reports from ONEMI, Chile

Latest status reports from SERNAGEOMIN, Chile

Latest webcam images of Villarrica, from SERNAGEOMIN

Latest Volcanic Ash Advisories from the Buenos Aires VAAC

Further information

Great video footage of the 3rd March eruption from 24Horas

Collections of photos and video from BioBioChile24Horas, Cooperativathe Guardian and SERNAGEOMIN.

Villarrica on Volcano Top Trumps

Villarrica pages at the Smithsonian Institution Global Volcanism Programme.


Castruccio, A. et al., 2010, Comparative study of lahars generated by the 1961 and 1971 eruptions of Calbuco and Villarrica volcanoes, Southern Andes of Chile, Journal of Volcanology and Geothermal Research 190, 297-311.

Rivera, A. et al., 2015, Recent changes in total ice volume on Volcan Villarrica, Southern Chile, Natural Hazards 75: 33 – 55

M van Daele, J Moernaut, G Silversmit, S Schmidt, K Fontijn, K Heirman, W Vandoome, M De Clercq, J van Acker, C Wolff, M Pino, R Urrutia, SJ Roberts, L Vincze, M de Batist, 2014, The 600 yr eruptive history of Villarrica volcano (Chile) revealed by annually laminated lake sediments, Geological Society of America, Bulletin doi:10.1130/B30798.1

Friday Field Photos: the Southern Volcanic Zone of Chile

Friday Field Photos: the Southern Volcanic Zone of Chile

If you are ever in Chile and have the chance to take a mid-morning flight south from Santiago towards Puerto Montt or Concepcion, make sure you try and book a window seat on the left hand side of the plane.  Once the early morning cloud has cleared, you could be in for a treat as you fly along the ‘volcanic front’, with spectacular views of Chile’s brooding volcanoes popping up from the landscape. Be sure to take a map, too, so that you can work out which one is which. The pictures below are roughly in order, flying from north to south – and several major volcanoes of the chain aren’t included.

There are several things to notice about these volcanoes – they are often in pairs, either as distinct but closely spaced mountains (Tolhauca and Lonquimay), or as ‘twin peaks’ forming the summit of an elongated massif (e.g. Llaima, Mocho Choshuenco). Many of the volcanoes are also clearly very young structures – forming wonderfully characteristic conical shapes (e.g. Antuco, Villarrica, Osorno). These cones must be younger than 15 – 20,000 years (and perhaps much younger than this), based on what we know about when the last major glaciation in the region ended. These cones sit on top of the lower-relief and older parts of the volcanoes, many of which have been reshaped by caldera-collapse, perhaps shortly after the ice retreated during deglaciation. The accessibility of the volcanoes of the Southern Volcanic Zone of the Andes makes this a wonderful place to study volcanic processes and volcano behaviour, both at the scale of individual eruptions, as well on the regional scale.

The river Cachapoal runs out of the Andes mountains, past the city of Rancagua

The river Cachapoal runs out of the Andes mountains, past the city of Rancagua

The saddle-shaped volcanic complex of Planchon-Peteroa (35.2 S), which last erupted in 2011.

The saddle-shaped volcanic complex of Planchon-Peteroa (35.2 S), which last erupted in 2011.

Cerro Azul volcano, Chile.

The spectacular ice-filled summit crater of Descabezado Grande volcano, Chile, at 35.6 S. The last eruption from this complex was in 1932, shortly after an eruption of the  nearby volcano Cerro Azul (or Quizapu).

View across the volcanoes of Tolhuaca (or Tolguaca, near ground) and Lonquimay (38.3 S). Both volcanoes are young, but it is not known when Tolhuaca last erupted. Lonquimay last erupted from 1988-1990.

View across the volcanoes of Tolhuaca (or Tolguaca, near ground) and Lonquimay (38.3 S). Both volcanoes are young, but it is not known when Tolhuaca last erupted. Lonquimay last erupted from 1988-1990.


The young cone of Volcan Antuco, 37.4 S. Its last known eruption was in 1869.


Twin-peaked Llaima (38.7 S) is one of the most active volcanoes of southern Chile, and last erupted in 2009.


Volcan Sollipulli (39 S) has a spectacular ice-filled summit caldera, but is not thought to have erupted since the 18th Century


Panorama across three young volcanoes, looking east: Villarrica (39.4 S) in front; the snow-covered sprawl of Quetrupillan in the middle ground; and the peak of volcan Lanin, on the Chile – Argentina border, in the distance.


Villarrica, with a characteristic thin gas and aerosol plume rising from the open crater at the summit.


The twin-peaked volcanoes Mocho Choshuenco (39.7 S). Choshuenco, thought to be the older vent, is the angular crag nearer the camera; Mocho is the small cone in the middle of the summit plateau. Mocho last erupted in 1937.


Looking across a bank of cloud towards volcan Osorno (front, 41.1 S), and volcan Tromen, in the background. Osorno last erupted in 1869; Tromen is thought to have last erupted in 1822.


Volcan Calbuco (41.3 S), which last erupted in 1972.

Data source: information on the recent eruptions of these volcanoes is all from the Smithsonian Institution Global Volcanism Project.

Further reading:

CR Stern, 2004, Active Andean volcanism: its geologic and tectonic setting. Revista geologica de Chile 31, 161-206 [Open Access].

SFL Watt et al., 2009, The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone. Earth and Planetary Science Letters, 277 (3-4), 399-407.

SFL Watt et al., 2013,The volcanic response to deglaciation: evidence from glaciated arcs and a reassessment of global eruption records, Earth-Science Reviews 122, 77-102.

Acknowledgements: my fieldwork in Chile over the past 10 years has been funded by NERC, IAVCEI and the British Council. Many thanks to my parents for introducing me to Chile and its volcanoes at the age of 7; and to Jose Antonio Naranjo and many others at SERNAGEOMIN for facilitating our continuing work in the region.

Chilean volcanoes: shaken, but not always stirred?

November 7th marked the 175th anniversary of one of the largest earthquakes to have struck northern Patagonia. The earthquake, which is estimated to have had a magnitude of 8, had an epicentre close to Valdivia, and was accompanied by significant ground shaking and subsidence as far south as Chiloe island, and a major tsunami that reached Hawaii.  The eyewitness reports of the time have been well documented. From a geological perspective, the key feature of the 1837 earthquake is that it occurred along a section of the plate boundary that has ruptured repeatedly, with great earthquakes in 1575, 1737 and, most significantly, in 1960  – which, with a magnitude of 9.5, is still the largest recorded earthquake globally. The 1837 earthquake struck just two years after the great Concepcion earthquake, of February 1835, which was exquisitely documented by Charles Darwin, among others.  Because of the location, adjacent to the long southern Chilean volcanic arc, and the frequency of large earthquakes in this region, both the 1835 and 1837 earthquakes have become critical pieces of evidence for the ongoing question of whether, and how, large earthquakes might lead to small triggered volcanic eruptions. Historical records from the region that include maps, expedition reports and navigational charts mean that the record of past eruptions in the southern parts of the central valley of Chile extend back into the 16th century and the earliest Spanish colonists.

Osorno map view from 1747

Map of southern Chile, and the northern part of Chiloe island extracted from ‘A new and accurate map of Chili, Terra Magellanica, Terra del Fuego etc.’ compiled by Emanuel Bowen in 1747. Active volcanoes of Osorno (vul. of Osorno) and, probably, Hornopiren (vul. of Quechucabi) are shown. From the Bodleian libraries, University of Oxford.

The 1837 Valdivia earthquake was followed by reported eruptions, on the same date, both at volcan Osorno, and Villarrica. Both volcanoes had already been in a state of activity on and off in the months or years prior to the earthquake, and both have long historical records of activity, so the observations are not necessarily surprising. One of the challenges of testing for cause and effect when it comes to possible earthquake-triggered eruptions is the likelihood of false reporting that arises from the natural tendency of people to conflate all sorts of observations and speculations in the aftermath of major events, like earthquakes. For example, both Villarrica and Osorno have also been recorded as having erupted shortly after the great earthquake of 1575, but neither observation is necessarily secure.

Volcan Osorno, overlooking Lago Llanquihue, Chile

Volcan Osorno, overlooking Lago Llanquihue, Chile

In contrast to the reports from 1837, the 1960 earthquake did not appear to have any major consequences for either system. Osorno has now been dormant since the late 19th century, while activity at Villarrica has rumbled on into the 21 st century.

Volcan Villarica, map view from 1759

Map of volcan Villarrica, from 1759. Reproduced in ‘Cartografia hispano colonial de Chile’, published in 1952 to mark the centenary of the birth of Don Jose T Medina. From the Bodleian libraries, University of Oxford.

Volcan Villarrica

Volcan Villarrica, with steam plume, viewed from Pucon.

Work is still in progress to investigate the consequences of the most recent great earthquake in the region: the Maule earthquake of February 2010. It remains possible that reported changes in activity at Villarrica in March 2010, seen in thermal infra-red satellite imagery, and subsequent eruptions of Planchon-Peteroa and Puyehue – Cordon Caulle may ultimately be linked to the rejuvenating effects of the earthquake, but this remains to be properly tested.

Of course, this is a question that is mainly of academic interest (in terms of understanding how eruptions are triggered), since most of the eruptions documented to have occurred in the immediate aftermath of great earthquakes are very small, and are most likely to occur at systems which have already been in eruption. The consequences of these eruptions are usually negligible, compared to the effects of the large earthquakes themselves. In recognition of the frequency of these potentially devastating earthquakes, the Chilean authorities (ONEMI, Oficina Nacional de Emergencia) are today holding an earthquake simulation across the schools of Santiago, as part of the programme of national preparedness for future emergencies.