Volcán Calbuco: what do we know so far?

27 Apr
Around midday on April 24, 2015, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this natural-color image of the ash and gas plume from Calbuco volcano in southern Chile.

Image of Calbuco volcano on April 24, 2015, from NASA’s Earth Observatory. Natural colour image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite. The narrow plume of ash and gas is being blown to the East, away from Calbuco and towards the town of San Carlos de Bariloche.

Detailed assessments of what happened during the April 22-23 eruption of Calbuco, Chile, are now coming in from the agencies responsible for the scientific monitoring of the eruption (SERNAGEOMIN) and for the emergency response (ONEMI). The volcano is well monitored and accessible, and as a result there has been a great deal of high quality information, and imagery, made available very quickly. In addition, there is a wealth of satellite remote sensing data, which together allow us to collect up some basic statistics about the scale of the eruption. So here are some summary statistics for now:

  1. This was the first explosive eruption of Calbuco since a small eruption that lasted 4 hours on 26 August 1972. In the intervening 42 years, there was an episode of strong ‘fumarole’ emission in August 1996, but no recent signs of unrest.
  2. The eruptions of 22-23 April began with little prior warning, and both formed strong, buoyant plumes of volcanic ash that rose high into the atmosphere – captured in some of the most amazing video and timelapse footage of an eruption anywhere in the world. The first eruption started at 18:05 (local time)  on 22 April; the ash column rose to 16 km, and ejected 40 million cubic metres of ash in about 90 minutes. The second eruption began after midnight (01:00 local time, on 23 April), with an ash column that rose to 17 km, and ejected 170 million cubic metres of ash over 6 hours. Based on the volume of material erupted (0.2 cubic km), and the eruption plume height, the combined phases of the eruption can be classified as a VEI 4 event, with an eruption magnitude of 4.4 – 4.6 (depending on the assumed density of the deposits).
  3. The Calbuco eruption was the third large eruption in this region of Chile in the past 10 years; but 4 or 5 times smaller than the eruptions of Chaiten (2008) and Puyehue Cordon-Caulle (2011).
  4. At its greatest extent, the ash cloud covered an area of over 400,000 square kilometres, affecting a population of over 4 million people in Chile and Argentina (modelled using CIESIN). Ash fallout was reported from Concepcion, on the Pacific coast, to Trelew and Puerto Madryn on the Atlantic coast of Argentina.
  5. The magma involved in the eruption was a typical andesite/dacite, containing volcanic glass and crystals of plagioclase and amphibole, with minor quartz and biotite.
  6. The SO2 gas release from the eruption was substantial – around 0.2 – 0.4 Million tonnes – probably some way short of the levels needed to have a significant impact on the climate system.
  7. The eruption was accompanied by dramatic pulses of lightning (a common feature in volcanic eruptions), and easily visible from space.
  8. At least 6500 people were evacuated as a result of the activity. The nearby town of Ensenada was badly affected by thick pumice and ash deposits, and lahars pose continuing hazards in the drainages that run off Calbuco, and into nearby lakes (Llanquihue, Chapo). The eruption has strongly affected some of the salmon fisheries in the region. Downwind, air transportation has been disrupted in Chile, Argentina and Uruguay.
  9. At the time of writing, SERNAGEOMIN note that the seismic activity has diminished somewhat , but the volcano remains at a red alert.

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

27 Apr IMG_0369

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.

IMG_6243

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).

Mocho

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.

IMG_0369

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

Acknowledgements

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.

References

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

Calbuco erupts. April 22, 2015.

23 Apr Volcan Calbuco (foreground), viewed on approach to Puerto Montt airport

Volcan Calbuco, which burst into eruption on April 22nd, is one of more than 74 active volcanoes in Southern Chile that are known to have erupted during the past 10,000 years. Unlike its photogenic neighbour, Osorno, Calbuco is a rather complex and rugged volcano whose eruptive record has posed quite a challenge for Chilean geologists to piece together.

Volcan Calbuco (foreground), viewed on approach to Puerto Montt airport

Volcan Calbuco (foreground), viewed on approach to Puerto Montt airport

IMG_6953

Calbuco’s volcanic neighbours, Osorno and Tronador.

The little that we do know about Calbuco’s eruption history comes from two sources: historical observations, and geological/field investigations. The historical record is not well known – other than that it has had repeated eruptions since the late-19th century. The eruption record prior to this is much less well known from written records, although the region has been populated for several millennia. The most spectacular recent eruption was in 1961, that ranked ‘3’ on the Volcanic Explosivity scale (VEI).

One interesting feature of Calbuco is that it is the only volcano in the area that regularly erupts magmas of an ‘intermediate’ composition (andesite), that contain a distinctive hydrous mineral, amphibole. This should make the eruptive products – particularly the far-flung volcanic ash component – quite distinctive. Preliminary work has identified the deposits of at least 13 major explosive eruptions from the past 11,000 years along the Reloncavi Fjord; but none of these have yet  been found further afield, even though they were the products of strong explosive eruptions (certainly up to VEI 5).

Calbuco is one of the many volcanoes in southern Chile that come under the watchful eye of the volcanologists from the Chilean Geological Survey, SERNAGEOMIN, and their Observatory of the Southern Andes (OVDAS); follow @SERNAGEOMIN for updates as the eruption progresses.

Further Reading

Find out more about our ongoing work on the volcanoes of Southern Chile

Fontijn K, Lachowycz SM, Rawson H, Pyle DM, Mather TA, Naranjo J-A, Moreno-Roa H (2014) Late Quaternary tephrostratigraphy of southern Chile and Argentina. Quaternary Science Reviews 89, 70-84. doi 10.1016/j.quascirev.2014.02.007 [Open Access]

Moreno, H., 1999. Mapa de Peligros del volcán Calbuco, Región de los Lagos. Servicio Nacional de Geología y Minería. Documentos de Trabajo No.12, escala 1:75.000.

Sellés, D. & Moreno, H., 2011. Geología del volcán Calbuco, Región de los Lagos. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geología Básica, No.XX, 30 p., 1 mapa escala 1:50.000, Santiago

Sellés, D et al., 2004, Geochemistry of Nevado de Longaví Volcano (36.2°S): a compositionally atypical arc volcano in the Southern Volcanic Zone of the Andes, Revista Geologica de Chile 31.

Watt SFL, Pyle DM, Naranjo J, Rosqvist G, Mella M, Mather TA, Moreno H (2011) Holocene tephrochronology of the Hualaihue region (Andean southern volcanic zone, ~42° S), southern Chile. Quaternary International 246: 324-343

Watt SFL, Pyle DM, Mather TA (2013) The volcanic response to deglaciation: Evidence from glaciated arcs and a reassessment of global eruption records. Earth-Science Reviews 122: 77-102

The great eruption of Tambora, April 1815

3 Apr
spring3

Map of the Sanggar peninsula, on the island of Sumbawa, Indonesia, and the crater of Tambora. From Heinrich Zollinger’s 1847 expedition to the crater, published in 1855. From University of Oxford, Bodleian Library Collection.

April 2015 marks the 200th anniversary of the great eruption of Tambora, on Sumbawa island, Indonesia. This eruption is the largest known explosive eruption for at least the past 500 years, and the most destructive in terms of lives lost, even though the precise scale of the eruption remains uncertain. The Tambora eruption is also one of the largest known natural perturbations to the climate system of the past few hundred years – having left a clear sulphuric acid ‘fingerprint’ in ice cores around the world, and evidence for a strong causal link to the ‘year without a summer‘ of 1816, and global stories of inclement or unusual weather patterns, crop failures and famine.

Much of what we do know about the eruption and its local consequences is down to the efforts of two sets of people: Stamford and Sophia Raffles; and Heinrich Zollinger. In 1815, Thomas Stamford Raffles was temporary governor of Java; the British having invaded in 1811. Shortly after the eruption of Tambora, he gathered reports from people in areas affected by the eruption, and put these together in an ‘account of the eruption of the Tomboro mountain‘, which was published first in 1816 by the Batavian Society for Arts and Sciences, and later published posthumously by his wife, Lady Sophia Raffles, in her biography of his life and works (Raffles, 1830).

There is a considerable scientific literature (see references below) which has documented the main phases of the eruption, which began in earnest on April 5, 1815, and built to an eruptive climax on 10 – 11 April 1815. It is thought that the volcano had been rumbling for some time prior to this, perhaps as early as 1812; and some of the contemporary records collected by Raffles suggest that the first ashy explosions may have begun by about April 1, 1815. An extract from a letter from Banyuwangi, Java, 400 km west of the Sanggar peninsula, describes this stage of the activity:

At ten PM of the first of April we heard a noise resembling a cannonade, which lasted at intervals till nine o’clock next day; it continued at times loud, at others resembling distant thunder; but on the night of the 10th, the explosions became truly tremendous. On the morning of the 3rd April, ashes began to fall like fine snow; and in the course of the day they were half-an-inch deep on the ground. From that time till the 11th the air was continuously impregnated with them to such a degree that it was unpleasant to stir out of doors. On the morning of the 11th, the opposite shore of Bali was completely obscured in a dense cloud, which gradually approached the Java shore and was dreary and terrific.

spring2

Heinrich Zollinger’s map of the inferred distribution of volcanic ash that fell across Indonesia following the eruption of Tambora in 1815. This may be the first example of an ‘isopach’ map of ash fallout from any volcanic eruption. From University of Oxford, Bodleian Library Collection.

The climactic phase of the eruption was very clearly described in an account by the Rajah of Sanggar, given to Lieutenant Owen Phillips, who had been sent to deliver rice for relief, and to collect information on the local effects of the eruption. ‘about seven PM on the 10th of April, three distinct columns of flame burst forth near the top of Tomboro mountain.. and after ascending separately to a very great height, their caps united in the air. In a short time the whole mountain next Sangar appeared like a body of liquid fire extending itself in every direction

In the main phase of the eruption, pyroclastic flows laid waste to much of the Sanggar peninsula, causing huge loss of life; and leaving a great collapse crater (caldera) where there had once been a tall volcanic peak.

Heinrich Zollinger was Swiss botanist, who moved to Java in 1841. In 1847, he led an expedition to Tambora and was the first scientist to climb to the crater rim since the eruption. In a short monograph, published in 1855, Zollinger describes his ascent of the volcano, documents the severe local impacts of the eruption, and details the numbers of people on Sumbawa affected by the eruption:

Location Killed in the eruption Died of hunger, or illness Emigrated
Papekat 2000
Tambora 6000
Sangar 1100 825 275
Dompo 1000 4000 3000
Sumbawa 18000 18000
Bima 15000 15000
Total 10100 37825 36725

Zollinger also estimated that at least 10,000 also died of starvation and illness on the neighbouring island of Lombok; and current estimates for the scale of the calamity are that around 60,000 people died in the region.

The bicentennial of the eruption of Tambora is a sobering moment to reflect on the challenges that a future eruption of this scale would pose, whether it were to occur in Indonesia, or elsewhere. Our present-day capacity to measure volcanic unrest should certainly be sufficient for a future event of this scale to be detected before the start of an eruption; but would we be able to identify the potential scale of the eruption, or its impact, in advance? Much remains to be done to prepare for and mitigate against the local, regional and global consequences of a repeat of an explosive eruption of this scale – and we still have more to learn by taking a forensic  look back at past events.

References

Auker, MR et al., 2013, A statistical analysis of the global historical volcanic fatality records. Journal of Applied Volcanology 2: 2

Oppenheimer, C., 2003, Climatic, environmental and human consequences of the largest known historical eruption: Tambora volcano, Indonesia, 1815. Progress in Physical Geography 27, 230-259.

Raffles, S, 1816, Narrative of the Effects of the Eruption from the Tomboro Mountain, in the Island of Sumbawa on the 11th and 12th of April 1815, Verhandelingen van het Bataviaasch Genootschap van Kunsten en Wetenschappen [via Google Books]

Raffles, S, 1830. Account of the eruption from the Tomboro Mountain, pp 241-250; in Memoir of the life and public service of Sir Thomas Stamford Raffles, F.R.S. &c: particularly in the government of Java, 1811-1816, and of Bencoolen and its dependencies, 1817-1824, with details of the commerce and resources of the eastern archipelago, and selections from his correspondence. London, John Murray.

Self, S, et al., 1984, Volcanological study of the great Tambora eruption of 1815. Geology 12, 659-663.

Sigurdsson, H. and Carey SN, 1989, Plinian and co-ignimbrite tephra fall from the 1815 eruption of Tambora volcano. Bulletin of Volcanology 51, 243-270.

Stommel, H and Stommel, E, 1983, Volcano weather: the story of 1816, the year without a summer. Seven Seas Press, Newport, Rhode Island.

Stothers, R.B., 1984, The great Tambora eruption in 1815 and its aftermath. Science 224, 1191-1198.

Zollinger, H., Besteigung des Vulkanes Tambora auf der Insel Sumbawa, und schilderung der Erupzion desselben im Jahr 1815. [Ascent of Mount Tambora volcano on the island of Sumbawa, and detailing the eruption of the same in the year 1815]

Links to online resources, and further reading

Bill McGuire ‘Are we ready for the next volcanic catastrophe?’The Guardian, 28 March 2015.

Gillen Darcy Wood ‘1816, The Year without a Summer’ BRANCH: Britain, Representation and Nineteenth-Century History. Ed. Dino Franco Felluga. Extension of Romanticism and Victorianism on the Net.

Haraldur Sigurdsson ‘Tambora: the greatest explosion in history’, a National Geographic photo gallery.

Tambora bicentennial – collection of papers in Nature Geoscience (Paywalled)

Gillen D’Arcy Wood’s Tambora; and an entertaining book review by Simon Winchester, author of ‘Krakatoa, the Day the World Exploded’

Anja Schmidt, Kirsten Fristad, Linda Elkins-Tanton (eds), Volcanism and Global Environmental Change, Cambridge University Press, 2015.

Villarrica erupts. March 3, 2015, Chile.

3 Mar
IMG_6893

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.

References

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

Landslides, lake tsunamis and the tragedy of Lago Cabrera

19 Feb

Fifty years ago, on 19th February 1965, a rock and ice landslide fell from the summit face of Volcan Yate in southern Chile. It was mid-summer, and was one of the warmest and wettest February records in that part of Chile on record. The debris slid rapidly down a narrow gully, losing at least 1500 metres in elevation, until it emerged into the southern end of a small montane lake. This triggered a small but devastating lake tsunami, that swept through the tiny lakeside community of Lago Cabrera just a few monents later. There was essentially no warning, no time to evacuate; and the event destroyed the village, killing twenty-seven people. This event was the worst volcano-related loss of life in Chile since the destructive lahars associated with the 1948 – 1949 eruptions of Villarrica.

Even in a country as volcanically active as Chile, it is the secondary consequences of volcanic activity that pose the most serious long-term threat to lives and livelihoods: notably lahars, triggered by the melting of snow pack, or remobilised by rainfall events. The Lago Cabrera tragedy is not thought to have been associated with any form of eruptive activity, but was a mass-failure event, not uncommon in mountain environments. In the ice- and snow-capped southern Andes of Chile and Argentina, the wider hazards associated with glacial-lake outburst floods and rock–ice avalanches remain incompletely documented, but there is a growing concern that these sorts of events might be increasing in frequency as a consequence of regional environmental changes.

 

Image

Small projectile embedded in woody debris, Lago Cabrera

Image

Remnants of buildings, destroyed in February 1965, on the shores of Lago Cabrera.

Image

View across Lago Cabrera to the apex of Volcan Yate.

 

Further Reading

S Doocy et al., 2013, The Human Impact of Volcanoes: a Historical Review of Events 1900-2009 and Systematic Literature Review, PLOS Current Disasters,  2013 Apr 16.  Link to database

P Iribarren Anacona et al., 2015, Hazardous processes and events from glacier and permafrost areas: lessons from the Chilean and Argentinian Andes, Earth Surface Processes and Landforms, 40, 2 – 21

M Stoffel & Huggel C., 2012, Effects of climate change on mass movements in mountain environments. Progress in Physical Geography 36, 421–439

SFL Watt, DM Pyle, JA Naranjo and TA Mather, 2009, Landslide and tsunami hazard at Yate volcano, Chile, as an example of edifice destruction on strike-slip fault zones, Bulletin of Volcanology 71, 559-574

C Witham, 2005, Volcanic disasters and incidents: a new database. Journal of Volcanology and Geothermal Research 148, 191-233.

Blog post on the ‘Tragedy of Lake Cabrera, Hornopiren, 19 February 1965′ (in Spanish)

Video (in Spanish) ‘La historia del lago Cabrera

The fate of volcanic ash in the environment

4 Dec Cartoon from  Bertrand et al. (2014) showing the fate of pumice and ash from the 2011 eruptions of Puyehue - Cordon Caulle, Chile

Over the past few years, we have been working to piece together the record of major post-glacial volcanic eruptions in southern Chile that have occurred over the past 18,000 years. This work started off with a search for volcanic ash layers that were preserved in road cuttings, or cliff faces other accessible geological locations in the region. Since then it has expanded to include the search for pumice and ash layers (or, more generically, ‘tephra’) in peat bogs and lake core sediments.

Sampling a peat bog in southern Chile.

Seb Watt sampling a peat bog in southern Chile.

By using the chemical compositions of the volcanic glass from each eruption to ‘fingerprint’ the deposits, we can now start to develop a framework in time and space of when volcanoes erupted, where they left deposits, and how large those eruptions were.

Depositional environments for volcanic ash in southern Chile, from Fontijn et al. (2014).

Depositional environments for volcanic ash in southern Chile, from Fontijn et al. (2014).

As well as looking at the deposits of past eruptions, which we can find in these cores and cuttings, recent eruptions in the region have also given us some new information on how the ash ends up where it does after an eruption.

Cuesta

Pale coloured band of volcanic ash at 44-46 cm depth in a peat core sample, Cuesta Moraga, Chile.

One of the fascinating stories that is starting to emerge from this work is just how patchy the preservation record can be – even for moderate to large explosive eruptions. In a really nice piece of work which has just been published, Sebastien Bertrand and collaborators looked at how volcanic ash and pumice ended up in the nearby lake Puyhue, after the 2011 eruptions of the volcano Puyehue – Cordon Caulle.

In this case, the dispersal of the ash clouds during the explosive phases of the eruption were very well constrained. As with most eruptions in this region, winds blew most of the ash clouds to the East, across Argentina, and there was no major phase of the eruption that deposited pumice and ash into lake Puyehue, to the West of the volcano. Instead, the thick deposits of ash and pumice that ended up in this lake – up to ten cm thick in places – must have been transported there by fluvial processes. Rainfall during and after the eruption would have helped to remobilise freshly fallen pumice and ash from the upper reaches of the watershed. This tephra would then have been washed downstream, and into the lake, where lake currents at different water depths then helped to redistribute the tephra across the different parts of the lake system.

Cartoon from  Bertrand et al. (2014) showing the fate of pumice and ash from the 2011 eruptions of Puyehue - Cordon Caulle, Chile

Cartoon from Bertrand et al. (2014) showing the fate of pumice and ash from the 2011 eruptions of Puyehue – Cordon Caulle, Chile

This study provides a really nice example of the complexities of trying to piece together the deposits from ancient eruptions from the sparse environmental records that are eventually preserved. In the lake Puyehue example, the sediments accumulating at teh bottom of the lake will be an excellent archive for the deposits – since they will eventually be buried and preserved. But since the deposits are entirely reworked, their characteristics in terms of both grainsize and thickness could be quite misleading, unless they are recognised as ‘secondary deposits’. Since volcanologists usually rely on pieceing together the areas affected by tephra deposition from the few locations where the deposits are both preserved, and then accessible to later discovery, and then use these data to work out how big the eruption was and which way the winds were blowing at the time, this new work will make us all have to think a little bit harder about our interpretations in the future.

References.

S Bertrand, R Daga, R Bedert, K Fontijn, 2014, Deposition of the 2011-2012 Cordon Caulle tephra (Chile, 40 S) in lake sediments: implications for tephrochronology and volcanology, Journal of Geophysical Research (Earth Surface), in press.

K Fontijn et al., 2014, Late Quaternary tephrostratigraphy of southern Chile and Argentina, Quaternary Science Reviews, 89, 70-84.   doi:10.1016/j.quascirev.2014.02.007  [Open Access]

 

 

Follow

Get every new post delivered to your Inbox.

Join 217 other followers