VolcanicDegassing

Chile

Maria Graham, and a large earthquake in Chile, 1822

Maria Graham, and a large earthquake in Chile, 1822

As news comes in of another very large earthquake in Chile – the third magnitude 8 earthquake along Chile’s Pacific margin in the past six years – this is a stark reminder of the destructive potential of these extreme natural events. These days we are used to the rapid, or near-real-time diffusion of news as these events unfold – in this case, as the tsunami ran along the Chilean coast, and propagated across the Pacific ocean. First indications are that the region that ruptured during the earthquake was a large section of the subduction zone plate boundary where the Nazca tectonic plate is sliding beneath the South American plate; close to an area that previously ruptured in great earthquakes in 1943, 1906, 1880 and 1822.

Map of historical rupture zones of large Chilean earthquakes. Source: United States Geological Survey.

Map of historical rupture zones of large Chilean earthquakes. The red dots show the locations of the 16 September 2015 earthquake and early aftershocks. Source: United States Geological Survey.

One of the earliest first-hand accounts in English of a large earthquake in this part of Chile comes from the writings of Maria Graham, who was living near Valparaiso in 1822; close to the source of the great earthquake of 19th November 1822, and within the region that was most hard hit by the event. Her journal – published in 1824 – records the event in great detail; and in particular, describes the dramatic coastal uplift that occurred as an immediate consequence of the event. A version of her report was later read to the Geological Society of London, where it caused a good deal of interest and, later, controversy.

View from Maria Graham's house. Bodleian libraries, Oxford, 4° R 56 Jur.

View from Maria Graham’s house. Bodleian libraries, Oxford, 4° R 56 Jur

Excerpts from Maria Graham’s ‘Journal of a residence in Chile, during the year 1822; and a voyage from Chile to Brazil, in 1823’,  London, 1824

November 20th, 1822.

At a quarter past ten [in the evening], the house received a violent shock, with a noise like the explosion of a mine. I sat still.. until, the vibration still increasing, the chimneys fell, and I saw the walls of the house open.. We jumped down to the ground, and were scarcely there when the motion of the earth changed from a quick vibration to a rolling like that of a ship at sea. The shock lasted three minutes. Never shall I forget the horrible sensation of that night. [Back in the house] I observed that the furniture in the different rooms .. Had all been moved in the same direction, and found that direction to be north-west and south-east.

Mr Cruikshank has ridden over from old Quintero: he tells us that there are large rents along the sea shore; and during the night the sea seems to have receded in an extraordinary manner, and especially in Quintero Bay. I see from the hill, rocks above the water that never were exposed before.

On the night of the nineteenth, during the first great shock, the sea in Valparaiso bay rose suddenly, and as suddenly retired in an extraordinary manner, and in about a quarter of an hour seemed to recover its equilibrium; but the whole shore is more exposed and the rocks are about four feet higher out of the water than before.

View of Quintero Bay

View of Quintero Bay, drawn by Maria Graham. Bodleian libraries, Oxford, 4° R 56 Jur.

December 9th, 1822.

in the evening I had a pleasant walk to the beach with Lord Cochrane; we went chiefly for the purpose of tracing the effects of the earthquake along the rocks. On the beach, though it is high water, many rocks with beds of muscles remain dry, and the fish are dead; which proves that the beach is raised about four feet at the Herradura. Above these recent shells, beds of older ones may be traced at various heights along the shore; and such are found near the summits of some of the loftiest hills in Chile.

In her journal accounts, Graham went on to speculate that repeated earthquakes could be responsible for the general elevation of land, and the building of mountains, in places like the Andes; themes that were later taken up by Charles Lyell, and then Charles Darwin – who was in Chile 13 years later, where he experienced the 1835 Concepcion earthquake firsthand.

Links

IRIS Special Event Page, Illapel – great collection of resources on the Illapel earthquake

United States Geological Survey – Illapel earthquake information

The Maria Graham Project, Nottingham Trent University

Profile of Maria Graham on TrowelBlazers

Volcán Calbuco: what do we know so far?

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.

Calbuco erupts. April 22, 2015.

Calbuco erupts. April 22, 2015.

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

Villarrica erupts. March 3, 2015, Chile.

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

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

The fate of volcanic ash in the environment

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]

 

 

Volcanoes Under the Ice

The ice-filled summit crater of volcan Sollipulli, Chile.

The ice-filled summit crater of volcan Sollipulli, Chile.

A fascinating story has emerged this week from a paper in Nature Geoscience by Amanda Lough and co-workers (Lough et al., 2013), on the discovery of a new volcano deep beneath the ice of the Western Antarctic Ice Sheet (WAIS).  The discovery is partly a story of scientists looking in a place where no-one had looked before; this case, using a network of seismometers, as a part of POLENET/ANET – a polar earth observing network. The instruments were laid out across a section of Western Antarctica, which is known to contain some large and relatively young volcanoes. The surprise from the data was the discovery of a deep source of seismic activity (earthquakes), in a location that didn’t match any of the existing volcanoes. The authors were able to show that the earthquake signals look like those from volcanoes, and not like those made from breaking rock or creaking ice; and they were also clustered into small swarms, both in time and space. All of this evidence points to the idea that these earthquakes relate to the movement of magma deep in the crust beneath a small volcano that was not previously known, and which hasn’t yet emerged above the ice. This is fascinating ‘discovery’ science, and poses all sorts of interesting questions about how and why the volcanoes in this part of Antarctica exist in the first place – a topic where little is known, but where there is a very timely recent paper by Wesley LeMasurier.  Of course, much of the press coverage has focussed on speculation about whether, or not, there might be calamitious effects for the West Antarctic Ice sheet in the case of an eruption (The short answer is no!).

One broader reason for my interest in the paper is that it links to the long-standing question of what happens when large volumes of ice are removed from volcanoes? On Earth, the main example of this relates to the end of the last glaciation, which began between about 18,000 and 20,000 years ago. The current hypothesis, which has been around for some time, goes like this. During the peak of glaciation, vast areas of the land surface can be buried under great thicknesses of ice – perhaps as much as hundreds of metres to kilometres. Then, during deglaciation, the ice retreats rapidly reducing the pressure on the rocks beneath. So far so good, but how could taking away some ice have any effect on volcanoes? One clue to the answer may come from Iceland. This is a part of the world where the mantle is hot enough at shallow enough depths, that there is a column of partially-molten rock that probably extends from about 40 km depth down to about 100 km depth. Here, where the rock is above its melting point, Charlie Langmuir and Dan McKenzie have shown that that amount of melt increases by about 1% for a pressure drop of 100 MPa. So removal of a 1000 m thick column of ice (at an Icelandic volcano) will translate into a pressure drop of 10 MPa, and an increase of melt fraction of 0.1% along the length of the 60 km melt column. This is to a change in the amount of melt produced of 60 m. This might not seem like much – but when you consider the full size of the melting region in the mantle, this could correspond to a considerable volume of melt produced simply as a result of ice removal. In Iceland, there is geological evidence for a pulse of eruptive volcanism that occurred very shortly after deglaciation – around 11,000 years ago. 

Moving back to Antarctica, the current idea is that the volcanoes beneath West Antarctica might also be fed from a plume, similar to that beneath Iceland and the Canary islands. So perhaps it is plausible that a similar explanation might also apply in Antarctica, and there might be a feedback on geological timescales between large-scale mass changes in the ice sheet, and the magma supply from depth? What is not clear, yet, is whether this same mechanism applies to the volcanoes that form above subduction zones. Here the melting process is a little different, driven primarily by the arrival of water into the mantle. So it is not clear how pressure changes due to changing ice load might lead to changes in melt production deeper down. It is also not yet clear, from the geological evidence, whether or not there were changes in rates of eruptions at the subduction zone volcanoes that were once covered with ice. This remains a work in progress!

References

Lough, AC et al., 2013, Seismic detection of an active subglacial magmatic complex in Marie Byrd Land, Antarctica,  Nature Geoscience (Advanced Online Publication, 2013/11/17/) http://dx.doi.org/10.1038/ngeo1992

Watt, SFL et al., 2013, The volcanic response to deglaciation: Evidence from glaciated arcs and a reassessment of global eruption records, Earth-Science Reviews, 122, July 2013, Pages 77-102, http://dx.doi.org/10.1016/j.earscirev.2013.03.007

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.

IMG_6868

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

IMG_6877

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

IMG_6887

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

IMG_6900

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.

IMG_6893

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

IMG_6917

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.

IMG_6939

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.

IMG_6972

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.