Our DAILY DOSE of DUST – VOLCÁN COPAHUE

Copahue on 17 April, 2016 (© Valentina Sepulveda ‏@valecaviahue, via Twitter – ¡Gracias, Valentina!)

Screenshots from the video: “Volcan Copahue 2016” by Nicolás Sieburger: “Nightly climb to our beautiful
volcano, the video was filmed inside the crater, 10 meters from the pyroclastic cone.”

Copahue can drive you mad with its caprices, at least if you live near enough. First it makes everyone jump, scientists and population alike, even causing a red alert put in place, then it goes on for years steaming innocuously or belching ash, with a bit of strombolian fireworks thrown in – you never know what it is really up to. I thought it worthwhile to find out what Copahue is capable of – how it behaved in the past and what to expect from it in the future.

Copahue ([koˈpawe] which translates as “sulphur waters” from the Mapuche language) is a 3001m-high stratovolcano. It lies in the eastern part of the Southern Volcanic Zone (SVZ) of the Andes, or more correctly, in the transition between the Central and Patagonian Andes, and directly on the border between the Bío Bío Region in Chile and the Neuquén Province in Argentina.

Preliminary geologic map of Copahue, showing outlines of Pliocene and Pleistocene calderas, post-caldera lava flows, faults, and fumaroles (not including the one in Del Agrio crater). Distribution of airfall tephra from the 3 main 1992 explosions is also shown. Contour interval, 100 m. (© A. Bermúdez and D. Delpino, via GVP)

It has grown within the 6.5 x 8.5 km wide Trapa-Trapa caldera, which in turn has formed at the western margin of another, the 20 x 15 km Pliocene Caviahue or Del Agrio caldera.
About 500 people live in Copahue, a village famous for its spa waters, and there are about 900 living in the town of Caviahue and an estimated 800 more in local indigenous Mapuche communities. Copahue volcano takes the position No. 9 of hazard ranking of the 91 active volcanoes in Chile. In recorded history Copahue has had 13 eruptions, basically all small ones at VEI=2. So, what caused the excitement in recent years? Well, one thing is that the two towns are located only 7 and 9 km respectively from the crater, with many houses and small settlements scattered along the Lomín/Bíobío and Queco rivers, and thermal baths and a ski station even nearer to the volcano…

 

THE VOLCANO

Initial studies at the beginning of the last century considered the El Agrio depression as a basin of glacial origin; years later the investigations of the 1980’s identified its origin as a caldera, and only at the beginning of this century, the volcano was recognized as a fissural eruptive  center associated with recent deformation.

 

Structural model of the Copahue volcanic complex with post-glacial vent alignments. (Bonali et. al 2016. For full description and context see here.)

Copahue began to form its shield-like structure ~1.2 Ma ago on the SW rim of the El Agrio caldera, creating a caldera of its own abt 0.5 Ma ago. Volcanism here is a result of both a) the regional stress field, imposed by the Nazca plate subducting under the South-American plate, and b) by local faults and grabens formed at the intersection of regional fault systems in a pull-apart basin, or transtensional structural system. During the Quaternary, the volcanic activity of Copahue was concentrated on the NE-trending, 90-km-long Callaqui-Copahue-Mandolegüe lineament (the longest in the SVZ), interpreted as a crustal-scale transfer zone. This fault line includes the Callaqui volcano to the SW, Copahue, and the Del Agrio caldera to the NE.

Sketch of the summit area (top) and locations of 1992 eruption deposits (bottom) at Copahue, 13 August 1992. The 60-m fracture that spawned a small
mudflow in the Del Agrio river is marked with an “f”. The approximate area shown by the summit-area sketch is enclosed by a box on the bottom drawing. (© O.
González-Ferrán, via GVP)

Today, this andesitic-basaltic stratovolcano has no less than nine craters lined up along a 2 km NE-trending fissure – activity has constantly progressed eastwards over time – complete with aligned parasitic cones and fissure-related pyroclastic flows. The easternmost crater, El Agrio, is historically the most active. It is 400 m wide and used to contain an acid lake with a pH value lower than 0.3 and liquid sulfur floating on its surface. From recent images it appears that the crater bottom is dry now and a cinder cone is building up around the active vent. Copahue has produced almost every possible sort of lava, from trachybasalt to rhyolite in its past, except for basalt. It is thought that magma at Copahue rises along vertical or subvertical fault planes from a possible magma chamber somewhere at 9-20 km depth. Cooled magma intrusions in the vertical faults will leave dikes, which can be seen in many locations around Copahue, sometimes, exposed out of the faulted rock by erosion, as free-standing “walls”.

Recent studies find that tectonic deformation is still going on in the area. For example, the Copahue Village Fault System shows open fractures in young lava flows, soil displacements etc.. Other relatively recent changes are vertical displacements ranging from 0.5 – 30m, usually a few meters, often showing open fractures as yet unfilled by sediments or soil. A host of new studies shows that Copahue experiences cycles of deflation and inflation associated with active fault systems that control the youngest magma pathways. These ducts are located in a relief zone between the Liquiñe-Ofqui fault system (that runs through the volcanic arc) and the fault zone of Antiñir-Copahue (located in the back arc). There is staggering evidence that these powerful systems have caused this relatively old volcanic center to magmatically and structurally reactivate, making it a special case of the southern zone of Argentine-Chilean active volcanoes.

The magma chamber(s)
Geological evidence shows that the area is a volcanic region much more extended than the Copahue edifice itself (leading to elaborate name constructs like “Caviahue-Agrio caldera-Copahue-volcano complex” or CAC in some literature). From various studies on the seismicity of Copahue and its surroundings it becomes apparent that the area E of the volcano (i.e. within the old Del Agrio caldera) is very active, with earthquakes concentrating around lake Caviahue. This would indicate that there are possibly magma reservoirs below that lake with a) around 40-50 volumetric percent of melted rocks, b) temperatures of about 700°C and c) at a depth of 9-20 km. A gravimetric exploration in 1975 showed a negative anomaly north of Caviahue Lake, which could indicate the position of a shallow magma reservoir located in the upper crust. The present active crater of Copahue volcano is located ~15 km west of this anomaly. In addition, close to Copahue village is a large crater-like depression called Anfiteatro, where two lava domes are emplaced.

COPAHUE’S LARGE AND IMPORTANT HYDROTHERMAL SYSTEM

Colorful rocks are a sign of chemical alteration (author not found)

Hot springs and warm pools and streams certainly are a great asset for the fortunate communities who can make use of them to draw tourists to their lovely spa resorts. The down side is that hydrothermal activity makes it so difficult to determine the behavior of volcanoes like Copahue, since large quantities of geothermal water underground will alter and erode the rock to make it unstable on one hand and may cause explosive, steam-driven eruptions on the other. The outer expressions of Copahue’s “waterworks” are the transient crater lake (letting out its waters through a notch in the crater wall), and several acidic springs on the slopes, all feeding into the rivers flowing down into the Del Agrio caldera and beyond.

Thermal baths, Aug 2012 (© Valentina Sepulveda ‏@valecaviahue, via Twitter)

Several geothermal field (Las Máquinas y Las Maquinitas) are very active with fumarolic activity at temperatures over 150ºC. This active hydrothermal system also produces a constant background tremor which makes it difficult for volcanologists to detect magmatic activity in the volcano. The abundance of hot waters greatly influenced the small phreatic to phreato-magmatic eruptions and isolated weak strombolian episodes in recent years. There is an important correlation between heat flow and the main geo-structural lineaments of the zone: The strong tectonic activity has produced secondary permeability, i.e. the ascent of hot fluids to higher levels through cracks and faults. These are feeding a crater lake in the El Agrio crater which emptied during the 2000 eruption, refilled, and disappeared again in 2014. From recent images it appears that the crater bottom is dry now and a cinder cone is building up around the active vent. Eruptions from this crater lake have ejected pyroclastic rocks and chilled sulfur fragments in the past.

Copahue, seen during an overflight 03/14 (left), and in October 2014 with the crater lake gone and a small cinder cone beginning to grow. (© SERNAGEOMIN)

Low magnification photo micrographs looking at key components from Copahue’s July 2012 tephra deposits. Fragments shown are less than 4 mm in diameter and were chosen to highlight morphologic differences between sulfur particles (A and B) and vitreous shards (C and D). (© R. Daga, via GVP)

One research team called Copahue a “beehive volcano” in their paper – they investigated the changing content of elements in crater lake and river water over time and came to a surprising result: The large amount of hot acid water that circulates within the volcano aggressively dissolves elements out of the rocks and leaves cavities of a combined volume of about 20 000–25 000 m³/yr, but that void space then fills up again with about equal amounts of liquid/native sulfur and precipitated silica. During the phreatic eruptions of 1992 and 1995, much of that liquid sulfur was ejected. This extensive rock dissolution has also weakened the internal volcanic structure, making – combined with the tectonic rattlings – flank collapse a serious volcanic hazard at Copahue.

Copahue has a volcanic spring-fed acid river with deposits of red hematite in the stream bed and abundant gypsum mineralization, and these fluids are saturated with K-jarosite. This riverbed may be a modern terrestrial analog of the Opportunity Rover landing site on the planet Mars. (Jarosite is commonly associated with acid mine drainage and acid sulfate soil environments. In 2004 jarosite was detected on Mars by a Mössbauer spectrometer on the MER-B rover, which has been interpreted as strong evidence that Mars once possessed large amounts of liquid water.) (Img. source)

From the eastern flank of the volcano emanate two hot acidic springs that are closely connected to the volcanic hydrothermal system. They converge approximately 500 meters downstream to form the headwaters of the upper Agrio river. These acidic waters affect the chemical composition of the entire hydrological system of the area (through lake Caviahue and the lower Agrio river) up to the town of Loncopué 80 km downstream. This fact represents “a rare example of the occurrence of hydrothermal fluids on the surface of the earth from a deep source with a strong magmatic signal” (GVP). Measuring the chemical properties and temperature of these waters continuously can be a means to detect changes in the volcano’s hydrothermal system. If, as happened in 2004, the temperature suddenly drops (to an extent that the crater lake froze over) and certain elements normally dissolved in the water disappear, one can suppose that something is afoot in the volcano. In the 2004 case, no eruption followed, but the event was attributed to a blockage in the fracture system that fed the crater lake due to oversaturation and precipitation after the arrival of hyper-concentrated deep fluids. It is thought that similar blocking of the hydrothermal pathways has caused the phreatic events during the 1990s.

 

COULD COPAHUE’S ERUPTIVE ACTIVITY BE “EARTHQUAKE-INDUCED”?

The Copahue magma pathway was affected by normal stress reduction after the May 1960 Valdivia earthquake, and the volcano erupted in July 1960 and 1961. The eruption in 2012 occurred after the 2010 Chile earthquake, also under “unclamping” conditions of the magma pathway… did the volcano respond to the earthquakes?

Tectonic setting of the Southern Volcanic Zone (SVZ). (© Bonali et. al 2016. For full description and context see here.)

Scientists are researching the question how do large earthquakes trigger volcanic activity, and there is a lot of discussion going on. Several authors point out that the delay between a big earthquake and the consequent volcanic events can be( from seconds) up to several years, because of the complexity of volcanic systems.
It was noticed that the overall eruption rate in the SVZ increased after both great Chilean earthquakes of August 1906 (Mw 8.2) and May 1960 (Mw 9.5), and this increase occurred one and 3 years after the earthquakes. Both earthquakes induced a normal stress reduction on volcano magma pathways, favouring dyke intrusion. It was also noted, in 2012, that seismicity increased in the region of Copahue after the Mw 8.8 earthquake that occurred 3 km W of the Chilean shoreline on 27 February 2010. At the same time, a progressive increase in fumarolic activity from the crater lake, El Agrio, was observed. Dense plumes of vapor and acidic gases were frequently seen between 200-300 meters above the crater rim, and deformation between 11/2011 and 04/2012 showed uplift with displacements up to 7 cm. Also in 2012, the acidity in lake-, river- and spring waters (pH2, Cl and F) showed unusually high values.

This is, very simplified, the idea of how it could work (to be taken with a grain of salt!): The normal state in Chile’s subduction zones would be one of building up stress – untill one of the major faults ruptures and causes a powerful earthquake, followed by a slow, viscous relaxation of the lower crust and upper mantle. This would release much of the pent-up stress in the back country’s rocks, causing faults to relax and some vertical ones to widen – allowing magma to rise in them (called “magma pathway unclamping”). Dynamic stress changes may also excite and promote ascent of gas bubbles, and consequently magma ascent. Large subduction earthquakes seem to be capable of favouring volcanic activity at Copahue at a distance of 257-353 km and up to 3 years afterwards. Time scale would depend on the different types of stress changes as well as regional and local tectonic settings.

 

(© Francisco Negroni ‏@Negronifoto, via Twitter)

 

RECENT DEVELOPMENTS since 2000

Historical records indicate a general phreatic and phreato-magmatic character over the last two centuries, while the most recent (since 2000) eruptive events, due to magmatic pulses, have a strombolian character.

The eruption in 2000 has been considered the most intense of the 20th century at Copahue volcano. It started on July 1st with emission of lapilli, ashfall, bombs and acidic mudflows. Some of the bombs, 13 cm in diameter, were collected at more than 8 km from the summit area. In five days, more than 50 explosions were reported. Incandescent pyroclastic flows down the cone were observed. The phreatic explosions moved to Strombolian explosions on July 6th, but moderate explosions with ash emission were reported daily at least for six weeks more. As in the 1992 eruption, intense seismic activity accompanied the explosions.

Copahue 12/2012 (© Antonio Huglich/AFP/Getty Images, or © ANP)

In December 2012 a gradually increasing, low-frequency, continuous tremor caused a Red alert from the Chilean authorities, while the Argentinian side raised to Orange. The tremor culminated in phreatic explosions in Copahue with a ~1.5km-high ash column, but afterwards the volcano seemed to behave himself and the alerts were lowered again. On 27/05/2013 the situation got a bit scary; SERNAGEOMIN reported: “During the last 24 hours the activity increased markedly, we recorded 10,931 earthquakes of low magnitude, with an average of 455 events per hour” and “The intensity and type of seismic activity observed in recent days, along with the deformation of the volcano, suggest, with high probability, that the rise of a magmatic body in the shallow layers of the volcano has entered a process of no return”. They also saw the possibility of a lava dome extrusion and associated phenomena. Also, at least three large sulfurous fumaroles from the crater had been detected. – This time, the towns within 25 kilometers around the volcano were evacuated due to the intense magmatic activity and tremors. After 10 days the Red alert was lifted.

Video of strombolian low to medium scale activity within Copahue crater. © Robin Campion, Universidad Nacional Autónoma de México “MVI 7230”, no date, published on YT on 3 Dec 2014:

 

Copahue from the Argentinian side. 22/03/2014 (© SERNAGEOMIN)

From that time on, the volcano held scientists and locals on their toes – or, in more scientific terms: the volcano was in a metastable equilibrium, i.e. any change in conditions could either turn into a full-blown eruption or quieten the volcano down. At times, there were constant ash emissions for weeks, or earthquake swarms numbering in the thousands. In March 2014, most concerning to the SERNAGEOMIN were the increasing SO2 emissions and inflation over the previous weeks, as well as pyroclastic flows and lahars. Another eruptive cycle began in October that year; during an overflight on 14/10/14 volcanologists from Sernageomin noted a rise in temperature to 350°C on the surface, and the crater lake, which was still present in March, had completely disappeared. Again, the combination of all these precursory events made it seem very likely that magma was ascending within the volcano.

Technicians from Sernageomin (Chile) installing monitoring equipment for Copahue on the Argentinian side. (© SERNAGEOMIN)

In an overflight in Oct. 2015 surface temperature was measured at <500°C, also a new feature was the nightly incandescence in Copahue’s crater, visible on the webcams. By the end of December SERNAGEOMIN stated this night glow was probably from strombolian eruption.

In the first half of 2016 Copahue got somewhat more relaxed but in June, new increases in activity parameters were recorded. This suggested a new intrusion of magma in the sub-surface layers, perhaps a small volume, as a function of the absence of significant signs of deformation in the volcano. The report for July states: During the entire period of this report, a constant tremor signal was noted, oscillating, mainly associated with the gas outlet and sporadic ash emissions from the El Agrio crater. – Weekly reports had, since 2012 and up to date, invariably stated that webcam and satellite images detected more or less continuous steam-gas-and-ash emissions rising above Copahue’s crater to altitudes of up to 4.6 km, interspersed with the occasional note of strombolian explosions. Alert level remains at Yellow with a no-go zone of 1.5 km around the crater.

Webcam views (© SERNAGEOMIN)

Video “Emisión de roca pulverizada en el Volcán Copahue” by SERNAGEOMIN (undated, possibly 11/2016) https://www.youtube.com/watch?v=UgtLzxcVUd4 (SERNAGEOMIN seem to have abandoned the use of the word ‘ash’ [Span. ceniza] and often replace it with ‘pulverized rock’ [Span. roca pulverizada] – which makes sense as ash in the common use would be burnt/oxidized materials, i.e. NOT the same as volcanic ash).

 

IS COPAHUE one of the “SAFE” VOLCANOES? Judge for yourself:

Copahue 12/2012 (© Antonio Huglich/AFP/Getty Images)

I have read that residents of the Copahue/Caviahue area don’t think much of the risks their volcano poses to them: It has never done more than ejecting a plume, and hopefully that will stay so… Yes, it is a beautiful place, next stop Paradise, and I can understand that they would rather see more tourists come along than more restrictions and “Access forbidden” signs. BUT…

There are of course the common risks that come with any more or less explosive volcanic eruption: hot or cold tephra falls, pyroclastic flows and lahars. Additionally, there is the internal instability of the edifice caused by dissolution of rocks by the hydrothermal acid fluids – which makes Copahue prone to landslides and flank collapses. And, still more important, there is a growing tendency for phreato-magmatic eruptions, which can be more violent than the ones caused just by residual heat and water. AND MOST IMPORTANT: So far there is no way to predict phreatic eruptions, no matter how sophisticated the monitoring equipment may be, no matter how much common sense you use when climbing up to the crater – if water trickles down near enough to the magma it can take just a split second and the mountain is roaring. And ROARING can mean DEATH.

Y LO MÁS IMPORTANTE: Hasta ahora no hay manera de predecir las erupciones freáticas, no importa cuán sofisticado sea el equipo de monitoreo, no importa cuánto sentido común se use cuando se está subiendo al cráter – si el agua se derrama cerca lo suficiente como para magma puede tomar sólo una fracción de segundo y la montaña está rugiendo. Y RUGIDO puede significar MUERTE.

I had a reason to write this in bold letters.

And then there is that – Pulverized Rock:
– A 2002 chemical analysis of fine ash particles observed an enrichment in the smallest size fraction of Copahue ashes for four elements (Arsenic, Cadmium, Copper and Antimony) which is of particular interest from an environmental and human health point of view. While Antimony is highly toxic and Copper and Arsenic very dangerous in higher doses/prolonged exposure, exposure to Cadmium can lead to a variety of adverse health effects including lung-, bone-, kidney diseases and cancer.
– In 2012 sampled water from rivers, lakes and springs showed low pH values of 2.5-4.4 and also high fluorine contents up to 7.9 mg/l which clearly exceeds the acceptable maximum of 1 mg/l for drinking water.
(These elements were leached out of the rock, either from water circulating inside the volcano or from ash fall into lakes and rivers.)
– Another study looking at the properties of ash from five volcanoes in the Southern Andes over a 20-year period found that Copahue was the one with by far the greatest amount of very fine ash of the particle size <4 μm. Those themselves are a health risk for lungs and eyes, but in combination with the toxic minerals fine ash is a pretty unhealthy mixture indeed.

Taken straight from an abstract of a chapter of the book “Copahue Volcano” (which is sold online chapter by chapter, one chapter costs as much as a third of the whole book!): “‘Risk assessment’ is a relatively new concept in Argentina… …nevertheless such eruptions represent a threat for the communities living in the surrounding areas of the emission centre, not only because of pyroclastic flows and tephra fall (the nearby villages, Caviahue and Copahue, have so far only experienced ash fallout), but also due to the possible formation of mud flows and flank collapse triggered by the volcanic activity. …the most recent ones (2000, 2012) showed an increasing explosive character… …risk assessment …calls for the implementation of the monitoring network in the Argentina side of the volcano, since the only currently active seismic stations (OVDAS) are located in the Chilean side of the volcanic edifice, … Moreover, the Chilean observatory adopts criteria of alert levels, which are distinctly different with respect to those of Argentina Civil Defense, producing misleading information to the population. The villages of Copahue and Caviahue are regarded as extremely vulnerable to possible future eruptions if larger magnitude events should occur. A review of the presently available potential hazard map, an improvement of people’s education about the volcanic risks and a more interactive cooperation between the Chilean and Argentina scientific and administrative institutions are some of the immediate countermeasures to be taken into account before a new explosive phase at Copahue.” (2015)

Copahue & Araucaria trees (Photo courtesy Jara Domingo) Nov 17, 2016

Copahue volcano, 29 August 2016 (© Valentina Sepulveda ‏@valecaviahue, via Twitter)

Lake Caviahue, 06 July 2016 (© Valentina Sepulveda ‏@valecaviahue, via Twitter)

Disclaimer: I am not a scientist, all information in this (and any of my other posts) is gleaned from the www and/or from books I have read, so hopefully from people who do get things right! 🙂 If you find something not quite right, or if you can add some more interesting stuff, please leave a comment.

Enjoy! – GRANYIA

SOURCES & FURTHER READING

– GVP, Copahue
– Mapa de Peligros / Hazard map Alto BioBio (PDF, Sernagemin)
– Active Tectonics and its Interactions with Copahue Volcano (2016; download only)
– Volcanic tremor and local seismicity at Copahue Volcano
– The 2012-2014 eruptive cycle of Copahue Volcano, […] (Abstr. 2015, PDF)
– Le Chaudron de Vulcain (Blog)
– The 2000 AD eruption of Copahue Volcano, Southern Andes (2004, PDF)
– Risk Assessment and Mitigation at Copahue Volcano (2015, book chapter, abstract only)
– Environmental geochemistry of recent volcanic ashes from Southern Andes (2011)
– Hydrothermal element fluxes from Copahue, Argentina: A “beehive” volcano in turmoil (2001, paywalled)
– Seguimiento geoquímico de las aguas ácidad del sistema volcán Copahue […] (Span., 2012)
(Geochemical surveillance of acidic waters from Copahue Volcano-Rio Agrio System: Identifying possible application for eruptive precursors)
– Copahue Volcano: An active volcano on the border between Argentina and Chile
– Geological interactive maps of Argentina
– BarilocheOpina.com (News)
– Video: “Volcan Copahue 2016” by Nicolás Sieburger

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