VolcanicDegassing

volcanic eruption

Living with volcanoes, and learning from the past.

Living with volcanoes, and learning from the past.

November 13th, 1985, is a date that is still etched in my memory. This was the day that the Colombian town of Armero was submerged beneath a catastrophic flood of volcanic rocks, mud and water; a lahar that had swept down from the summit of the volcano Nevado del Ruiz, erupting about 40 kilometres away. For days, terrible scenes of anguish and despair filled our television screens, as rescuers struggled desperately to help the survivors, and recover the many thousands of victims. Thirty years on, and Colombia has one of the most sophisticated national volcano monitoring systems in the world, run from a network of observatories by the Servicio Geologico Colombiano (SGC). But what of the people of Armero; the survivors, and those who still live at the foot of the restless volcano, Nevado del Ruiz?

Over the past year, researchers from the University of East Anglia and the ‘STREVA‘ project have been working with the SGC and a filmmaker, Lambda films, to collect oral histories, to explore what people recall from that fateful day, and to learn more about how people live with the volcano today. The result is three short films: beautifully shot, tremendously moving, and well worth a few minutes of your time.

 

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

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]

 

 

There’s (volcanic) dust in the archives

There’s (volcanic) dust in the archives

There’s not much that beats the thrill of discovery.. particularly when it turns up in your own backyard.  This summer, I have been on the hunt for records and reports of the 1902 eruptions of St Vincent, a lush volcanic island in the Eastern Caribbean. There are indeed many reports from this eruption, carefully documented in official records from the time. But, more surprisingly, there are samples – and many of them in the UK: packets, vials and boxes of ash; chunks of rock and more, in museum collections and archives in both the Natural History Museum, and at the British Geological Survey. Here is just a snapshot of some of the incredible samples from the British Geological Survey Archives.

From the BGS archives

Four vials of volcanic ash – all collected on Barbados. The smallest vial is of ash from the 1812 eruption of St Vincent. The three other vials are samples of ash that fell on Barbados during eruptions between May 1902 and March 1903.

Along with the samples are the original envelopes in which they were sent, and handwritten notes documenting the sample: priceless tools, when you want to look back at an eruption that took place over 100 years ago.

1902 Barbados ash

1902 Barbados ash sample sent to Horace Woodward, who was in charge of the Geological Survey’s office in Jermyn Street, London, at that time – which included the Museum of Practical Geology. Memo reads ‘Dust from Mt Soufriere St Vincent, collected on the deck of the SS ‘Statia’ lying at Barbados, 90 miles distant, travelling against a strong S E wind and covering everything to the depth of 5 inches. 1903′.

Some of these samples are timed and dated, and can be linked to particular phases of the eruption. Here is one example – of the ash that fell during the opening stages of the eruption on Barbados.

First hour

‘Volcanic dust collected at Barbados during the night May 7-8 1902. This spec. fell during the first hour’. Collected by WG Freeman, a botanist at the Imperial Department of Agriculture for the West Indies in Barbados.

Other samples can be used to map the distribution of ash and coarser samples that fell across St Vincent – here’s an example of a ‘gravel’ grade sample from Rosebank on St Vincent.

1902 ash

1902 tephra sample collected on St Vincent by  Henry Powell, Curator of the Botanic Station on St Vincent. ‘Sample of volcanic sand which fell at Rosebank (Leeward) on night of 3rd and morning of 4th Sept. 1902’

Among the most amazing discoveries, are examples of damage to economically valuable plants – this one, a sample of Breadfruit leaf that was damaged during the latter stages of the eruption in March 1903.

image

‘A leaf of the Bread Fruit Tree (Artocarpus incisa) gathered in St Vincent about 12 miles from the Soufriere and showing perforation caused by volcanic stones etc.’ Collected by WG Freeman in 1903.

Together, these sorts of samples will allow us to go back and investigate what was actually happening during the eruption, in a way that is rarely possible, even for modern events.

Links – read more about the eruptions of St Vincent on the London Volcano blog.

The eruption of Kelut, Java, February 2014

Image of the ash plume from Kelut, drifting across the Indian Ocean on 14th Feb, 2014. NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE).

Image of the ash plume from Kelut, drifting across the Indian Ocean on 14th Feb, 2014.
NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE).

I have used storify.com to put together a synopsis of the February eruption of Kelut, Java, Indonesia. There are some additional links to more detailed posts and related information below.

Related posts

Collections on Storify

Links for further information on activity and monitoring

The eruption of Kelut, Gunung Kelud, Java, February 2014

The dramatic eruption of Gunung Kelud (Kelut volcano, Java, Indonesia) provides excellent examples both of how quickly information can spread around the world during unfolding volcanic crises; and of the capacity that we now have for tracking and analysing volcanic eruption plumes in near real time.

  1. Kelut is a dangerous volcano with a volatile history, and the lead in to the latest eruption was short. The first images of the eruption from @hilmi_dzi caught the rapid lofting of the plume.
  2. And, about 90 minutes later, also from @hilmi_dzi, the spectacular lightning show that often accompanies ash-rich plumes. In this image, there is also a clear glow from the core of the plume, where the hot volcanic mixture of ash and gas is emerging from the vent.
  3. Earth pic of the day. Indonesia’s Mount #Kelud volcano erupts with static discharge lightning. Credit: @hilmi_dzi pic.twitter.com/ymG2ItUfEq
  4. Indonesia is well prepared for volcanic emergencies, with over 130 active volcanoes, and major recent eruptions at both Sinabung (on Sumatra) and Merapi (on Java); a theme picked up both by the Indonesian press, and in social media posts.
  5. Front Page, Feb. 15: Mt. Kelud’s eruption displaces thousands, halts flights, spews ash pic.twitter.com/zQXyaF3b9H
  6. Volcanic ash in Yogyakarta in 2010 (eruption of Merapi) and 2014 (eruption of Kelut)
  7. #jogja Foto Perbandingan dampak hujan Abu Vulkanik di tugu ,Merapi 2010 Kelud 2014 pic.twitter.com/jnUkmMJypa via @JogjaMedia| @LensaJogja
  8. Explosive volcanic eruptions pose a significant threat not only to communities living around the volcano, but also to air traffic. In this case, the Volcanic Ash Advisory Centre in Darwin, Australia, were quick to respond with forecasts of the likely spread of the ash in the atmosphere.
  9. Estimated extent and prediciton of the ash plume (VAAC Darwin). pic.twitter.com/XPchidd6Bt
  10. In the early stages of an eruption it can be quite hard to gauge how high the ash has been lofted in the atmosphere; and this is also something that can change quickly depending on the strength of the eruption.
  11. Kelut #volcano in Java is erupting – Darwin VAAC reports ash cloud to 15 km altitude  http://www.bom.gov.au/products/IDD65295.shtml 
  12. #Darwin VAAC says volcanic ash plume observed to FL550 500NM WSW of Mt Kalud, Java. Some flts in region cnld/diverted pic.twitter.com/VLXd4i8XCB
  13. For an explosive eruption of this scale, remote-sensing measurements from satellites can very quickly provide the cofirmation needed on the ground in terms of the scale of the eruption, and the location of the ash cloud. As explained on the NASA Earth website, satellites first detected the eruption at 11.09 pm local time (20 minutes before @hilmi_dzi‘s first photo, above); and at 12.30 am (local) the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured an image of the top of the plume rising above the clouds.Shortly after, a laser-ranging instrument (Cloud-Aerosol Lidar, CALIOP) flew over on board the CALIPSO satellite, providing the first direct evidence that the plume top had reached between about 20 km and 26 km height.
  14. A satellite recorded ash from Mt. Kelut at an altitude of 20 kilometers (12 miles).  http://1.usa.gov/1gFqkY5  pic.twitter.com/J1Q7OPvhV9
  15. Peter Webley expands on this in a blog post, showing a reconstruction of the plume in cross section.
  16. Volcanic Activity in the North Pacific and beyond: Visualizing the Kelut Volcano eruption cloud in Go…  http://volcanodetect.blogspot.com/2014/02/visualizing-kelut-volcano-eruption.html?spref=tw 
  17. Volcanologists and atmospheric scientists are quite interested to know how high eruption plumes reach because that information tells them both about the strength of an eruption (the stronger the eruption, the higher the plume); and also about the potential of an eruption to have an influence globally, which is usually thought to require an eruption to loft material into the stratosphere.  In this case, it appears that some of the plume did intrude into the stratosphere; but in fact the first look at the potential gas emissions (in particular sulphur dioxide) suggests that these are actually rather small.
  18. SO2 from #Kelud drifts over Indian Ocean.
    SO2 mass is modest – no measurable climate impact expected #climatechange pic.twitter.com/CSaxanK1sH
  19. Perhaps of more (academic) interest to scientists is the structure of the expanding ash cloud itself – notice the ripples visible in the infra-red image above.
  20. CALIPSO lidar data for #Kelud eruption show nice gravity waves in the umbrella cloud at ~19 km altitude pic.twitter.com/V3yqFGb4YP
  21. The eruption also literally sent soundwaves around the globe, with an infrasound signal detected by the global Comprehensive Test-ban Treaty Organisation array, as well as other infrasound networks – a promising tool in monitoring activity at the world’s active volcanoes.
  22. Global infrasound from the 13 February 2014 Kelut Volcano eruption in Java!  http://newsroom.ctbto.org/ 
  23. Earth Observatory of Singapore gets a sound check for their new infrasound station from #Kelud/#Kelut volcano. Will improve SE Asia coverage
  24. Across Java, of course, the eruption has caused substantial disruption with reports of over 100,000 people being evacuated, a number of fatalities, and disruption to transport networks due to the fallout of ash across a wide portion of Java. The tweets and images below capture just a little of the scale of the misery caused by this event.
  25. Airport to and from Surabaya, Yogya, Solo, Bandung are still closed until 6:00 am tomorrow due to volcanic eruption of Mt Kelud, East Java.
  26. Ash covers this airplane from the eruption of Mount Kelud near Java in Indonesia. #737 #Boeing pic.twitter.com/5HSDGN8dmm
  27. Volcanic ash covers a plane at Yogyakarta airport, about 200 km west of the Mount Kelud volcano on Java pic.twitter.com/TvDw7H9l8H
  28. Juanda Airport in Surabaya after eruption of Mt. Kelud, 1 of 4 airports on Java reportedly closed pic.twitter.com/4AxxVk8Kox via @madhannnn
  29. @AP Sat, Feb 15th. Volcanic ashes of Mt. Kelud, at Adisucipto Int’l Airport in Yogyakarta, Java, Indonesia. pic.twitter.com/NizhwiHyh6
  30. Everyting is grey.. I can’t see the way..
    Volcano ash because of Mt.Kelud eruption
    #grey #Yogyakarta http://instagram.com/p/kd9QFsCW9e/ 
  31. Like a dead city.. taken from upstairs.. the trees and houses are covered by the ash of Mt. Kelud…  http://instagram.com/p/keDmSiCBaa/ 
  32. Suasana Puri Timoho Asri Baru II pasca hujan abu vulkanik Gunung Kelud . Hujan salju man 😀 #nofilter  http://instagram.com/p/keK63PyzXb/ 
  33. More ash, this time from Mount Kelud in Indonesia, in today’s #bikepic from Getty Images. pic.twitter.com/tBrQldxhkP
  34. The eruption of Mount Kelud in Malang, on the island of Java in Indonesia
    A duck walks through the mud and ash. pic.twitter.com/bP6vYFekzA

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August Anniversaries: the eruption of Krakatoa

August 27th marks the anniversary of the culmination of the great eruption of Krakatoa (or Krakatau) in Indonesia in 1883. This devastating eruption has become the archetype of a volcanic catastrophe, even though it was a geologically modest example of a ‘caldera forming’ event. The eruption of Krakatoa quickly made the headlines around the world, in part because newly installed undersea cables allowed the news of the event to be wired rapidly across the globe.

Precursory eruption of Krakatoa in May 1883. From Symonds (1888).

Precursory eruption of Krakatoa in May 1883, several months before the climactic events of August 1883. From Symons (1888).

The Krakatoa eruption was one of the first major eruptions to be intensively studied by scientists. The journal Nature published an editorial explaining the ‘Scientific Basis of the Java Catastrophe’ shortly after news of the eruption broke, and over the next few weeks published reports with the first descriptions and explanations of some of the many widespread effects of the eruption – from the appearance of great floating rafts of pumice, to the many oceanic, atmospheric and other phenomena that accompanied the event. In February 1884, the Royal Society set up the Krakatoa committee, chaired by a meteorologist George Symons, to collect information on ‘the various accounts of the volcanic eruption.. and its attendant phenomena’, including ‘authenticated facts respecting the fall of pumice and dust .. unusual disturbances of barometric pressure and sea level.. and exceptional effects of light and colour in the atmosphere‘. These results were published in 1888 in a wonderfully illustrated monograph, which still stands as one of the most complete accounts of a major volcanic eruption and its widespread effects.

 Drawings of views of Krakatoa rock samples in thin section, under a microscope.  This set of images are of lavas from Krakatoa. These are quite rich in crystals (white feldspar; green pyroxene), set in a fine matrix of glass (colourless to brown).  Images on the left: about 1 cm across; on the right – about 1 mm across.

Drawings of microscope views of Krakatoa rock samples in thin section. This set of images are of lavas from Krakatoa, from Symons (1888). These are quite rich in crystals (white feldspar; green pyroxene), set in a fine matrix of glass (colourless to brown). Images on the left: about 1 cm across; on the right – about 1 mm across.

 Drawings of views of 1883 Krakatoa pumice and ash samples in thin section, under a microscope.  The pumice samples are mainly made of glass (very pale colour) with gas bubbles.  The top 4 images are each about 1 cm across, and show the texture of lumps of pumice.  The bottom two images are each about 1 mm across, and show the ‘ash’ that fell over a thousand miles away from Krakatoa, onto the ship Arabella (left), and the ‘ash’ formed by grinding up a sample of pumice.

Drawings of microscopic images of 1883 Krakatoa pumice and ash samples . The pumice samples are mainly made of glass (very pale colour) with gas bubbles. The top 4 images are each about 1 cm across, and show the texture of lumps of pumice. The bottom two images are each about 1 mm across, and show the ‘ash’ that fell over a thousand miles away from Krakatoa on the ship Arabella (left), and the ‘ash’ formed by grinding up a sample of pumice. From Symons (1888).

The most celebrated impact of the Krakatoa eruption in terms of science was the recognition that the many optical effects that followed the eruption, including both spectacular sunsets (an example from London, in November 1883, below) and the discovery of ‘Bishops’ Rings‘, must be  the consequences of the global spread of volcanic pollutants, high in the atmosphere. We now know that the major constituents of this haze were tiny droplets of sulphate, forming a thin aerosol layer in the stratosphere which scattered and absorbed incoming solar radiation.

Sunset at Chelsea, 4.40 pm,  November 26th, 1883. From Symonds (1888).

Sunset at Chelsea, 4.40 pm, November 26th, 1883. From Symons (1888).

Although the Krakatoa eruption was one of the largest eruptions of the past 200 years, it is not exceptional in comparison to other eruptions from the geological record. In terms of eruption ‘size’ it rates as a ‘6’ on the Volcanic Explosivity Index, having erupted an estimated 12 cubic kilometres of magma. Eruptions of this sort of size occur once every 100 – 200 years around the globe; while the largest known explosive volcanic eruptions erupt many thousands of cubic kilometres of magma over a very short period of time. Krakatoa remains the best documented example of a ‘caldera-forming’ eruption, during which an entire volcanic edifice collapses. In this case, the eruption and the formation of the caldera had catastrophic consequences for tens of thousands of people along the shores of Java and Sumatra, as a series of major tsunamis triggered by these events swept ashore.

Reference

G.J. Symons (Editor, 1888), The eruption of Krakatoa and subsequent phenomena.  Report of the Krakatoa Committee of the Royal Society.  London : Trübner & Co.

Links to some other posts on Krakatoa

David Bressan’s excellent post for the Scientific American Blog

Bill McGuire’s post on Krakatoa for the OUP Blog

Jeremy Plester’s Weatherwatch piece for The Guardian

Cynthia Wood’s post for Damn Interesting

A page on the Krakatoa eruption from the United States Geological Survey

Timelapse volcanoes in Google’s Earth Engine

With the marvels of technology and the generosity of Google and NASA, we can now sit back and watch the back catalogue of volcanic eruptions using the magnificent Google Earth Timelapse of Landsat images. Here are just a few that I have picked out..

Enjoy, and do send more suggestions!

Anatahan, Marianas, erupted in 2005.  Anatahan Timelapse

Chaiten, Chile. Erupted in May 2008: look for the splash of ash.  Chaiten Timelapse

Miyakejima, Japan – a spectacular caldera-forming event in 2000.  Miyakejima Timelapse

Pinatubo, Philippines. Major eruption in 1991; thanks to Ron Schott for this.  Pinatubo Timelapse

Soufriere Hills Volcano, Montserrat. Erupting since 1995: watch the island grow.  Montserrat Timelapse

Lake Voui, Aoba volcano, Ambae island, Vanuatu, erupted in 2005-6.  Lake Voui Timelapse

Santiaguito Volcano: Ninety Years and Counting.

Santiaguito Volcano: Ninety Years and Counting.

Santiaguito volcano, Guatemala, burst into life in 1922 and is now the second longest continuing eruption. It has outlasted both Stromboli (Italy) and Sangay (Ecuador), both erupting since 1934, and is only outdone by Yasur (Vanuatu), which has been erupting at least since 1774, when first visited by Captain Cook.

These long-lived eruptions give us an unusual opportunity to use the slowly-extruded products to peer deep into the magma plumbing system. Santiaguito itself is now a rubbly complex of blocky lavas and domes that nestle in the crater formed by the explosive destruction of Santa Maria volcano, Guatemala, in 1902, in one of the largest eruptions of the last century.

View of the lava domes of Santiaguito volcano, from the flanks of Santa Maria, Guatemala

View of the lava domes of Santiaguito volcano, from the flanks of Santa Maria, Guatemala

After a violent beginning, Santiaguito has grown slowly (rather less than 1 cubic metre of lava/second) and in pulses for the past 90 years. Bill Rose, who has worked on Santiaguito since the early 1970’s, has documented this history very nicely. For many years, Santiaguito has been a magnet for geophysical and remote-sensing field campaigns, both because of its rather regular ash and gas explosions, and the fact that it is relatively accessible and very closely monitored by INSIVUMEH.  Rather less obligingly, though, the volcano is often cloud-bound by mid-morning, at least during the dry season, when moist westerly winds roll in from the Pacific.

IMG_5235

Explanatory poster, showing the fuming dome of Santiaguito sitting in the scar of the 1902 eruption crater, Santa Maria.

While Santiaguito has only a very slow growth rate, at the lower end of what is typical of actively-extruding domes, it poses major hazards to a number of local communities.

View of the Caliente dome, Santiaguito volcano, Guatemala

View of the Caliente dome, Santiaguito volcano, Guatemala

Lahars are common in the rainy season, and transport the accumulated loose talus from the flanks of the domes downstream, intermittently causing severe damage. Ash deposition can cause disruption to a wider community, extending both to the Fincas and cloud-forest coffee plantations or, more rarely, to agricultural and urban centres further afield, such as Xela (Quetzaltenango).

This way please.. coffee-bean receptor at Finca el Faro, on the flanks of Santa Maria volcano, Guatemala.

This way please.. coffee-bean receptor at Finca el Faro, on the flanks of Santa Maria volcano, Guatemala.

Receny years have seen several episodes of elevated activity at the volcano, and in this past week, Santiaguito has experienced another such phase. As reports from CONRED make clear, this elevated activity culminated in a large-scale slope failure from the active dome, Caliente, triggering pyroclastic flows and lofting ash plumes high into the atmosphere. The rainy-season legacy of these events will most likely be more lahars, as drainages now charged with debris become unclogged and rapidly incised.

Typical deeply-incised drainage channel, high up on slopes of Santiaguito, with recent ash fall on the vegetation.

Typical deeply-incised drainage channel, high up on slopes of Santiaguito, with recent ash fall on the vegetation.

My own interest in Santiaguito is in the long-term story of the volcanic plumbing system recorded in the rocks that have been progressively removed from the conduit during the eruptions of the past 90 years. Jeannie Scott has recently completed a study of this for her PhD (funded by NERC), working on samples that span much of the eruption history. The remarkable feature is the surprisingly simple story that emerges.  The 1902 eruption evacuated a large volume of dacite magma with a silica content of about 66 wt%. The 1922 eruption appears to have begun by emptying what was left behind of this pool of melt from 1902, and since then the volcano has been erupting increasingly silica-poor magmas, presumably tapping deeper into the plumbing system. The latest lavas analysed (from 2002) have about 62% SiO2. These observations suggest that future lavas may continue to get progressively more silica-poor; as they do so, they may also get warmer and a little less viscous, depending on conditions at depth. Unfortunately, in the process of slow extrusion, the lavas lose much of their dissolved gas, crystallise and eventually quench, so that it is quite a challenge to track back to the ‘original’ conditions under which the magmas were stored. This still leaves several unresolved puzzles: how is it that the conduit system can remain open, allowing magma to continue to leak out to the surface? And what is it that drives the long-term pulses of eruptive activity?  Answers to these questions will probably emerge once we have a better understanding of the full spectrum of long-lived dome-forming eruptions at andesitic volcanoes, such as those at Soufriere Hills (Montserrat), Colima (Mexico) and Merapi (Indonesia).

Links to further reading:

JAJ Scott et al., 2013, Geochemistry and evolution of the Santiaguito volcanic dome complex, Guatemala, Journal of Volcanology and Geothermal Research 252, 92-107.

JAJ Scott et al., 2012, The magmatic plumbing system beneath Santiaguito volcano, Guatemala, Journal of Volcanology and Geothermal Research, 237–238, 54–68.

Update: February 2013.

Jeannie Scott has now written and made freely available a colour booklet describing Santiaguito volcano and its activity, and a poster summarising recent work on the volcano.

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.