If you think back to the fall, I asked Eruptions readers to submit questions for Dr. Shan de Silva (right) from Oregon State University, who has been in the news for research at the inflating Uturuncu volcano (below) in Bolivia. He is also the resident volcanologist at Volcano World, a website I know many of us use regularly. Well, the answers are here! I offer a big "thank you" to Dr. de Silva for taking the time to tackle some of the great questions you all submitted.
Pieter: Is it true that certain volcanic areas go through 'caldera-forming phases'? A certain period of time in which volcanic activity is high and the caldera-forming eruptions are more common. For example, most of the calderas in the Rift Valley in Africa were formed during the late-Pleistocene, but ever since the Menengai eruption there hasn't been a caldera forming eruption that I know of.
Are so called 'supervolcanoes' regular strato/shield volcanoes before their first major eruption?Dr. de Silva: These are great questions that deal with something very close to my heart which is the critical importance of heat delivery to a volcanic system. I am going to take these two questions together as they deal with similar issues. The first issue is that not all calderas are the same. I am going to deal with andesitic to rhyolitic calderas (high silica content) that are formed through explosive volcanic processes and not basaltic calderas like Kilauea that are drainage calderas. Stratovolcanoes or composite cones (e.g. Crater Lake, Vesuvius) and shield volcanoes (Menengai, Newberry) tend to form calderas through collapse of the upper parts of their edifice and are typically quite small <10km in diameter. Larger 20 – 80 km calderas (Valles, Galan, Long Valley, Yellowstone, Toba, etc. getting into supervolcano territory here), form when the entire crust above the chamber collapses to form a depression. Any pre-existing composite cones or shield volcanoes would be swallowed up by this process.
Any individual volcano or volcanic system (temporally and spatially linked magma system) can wax and wane as a function of magma supply which is ultimately a function of the heat being delivered to the system. So small systems like Crater Lake or Vesuvius generally sputter along but then could have an explosive eruption that forms a caldera. Supervolcanoes are cyclical as well. The key is the rate that heat and magma are delivered to the shallow magma chamber from which eruptions initiate. If heat delivery is too slow then large magma batches can’t form because they would solidify after some time, but if heat is delivered rapidly then the magma stored in a chamber can remain “viable” (or eruptible) and grow – this is called the incubation rate. If the incubation rate is low (high heat flux) then each natch of magma does not have time to solidify before the next batch of magma arrives, keeping the system viable. A model that Patricia Gregg here at OSU is developing also shows that this incubation rate is important in keeping the rocks around the magma chamber warm thus allowing chambers to expland without breaking the rocks. So in both large and small systems formation of a viable batch of magma is critical and this is controlled by the rate of heat input (which is through magma delivery). So a caldera forming eruption could be seen as the final signal of increased heat (and magma) input into a volcanic system. This is cyclical. In answer to your second question, there is a clear difference between composite cones and supervolcanoes in terms of the size of their eruptions. The largest eruptions from the former are <100 km^3 while supervolcanoes are >1000 km^3. Supervolcanic eruptions occur less frequently and their cycle times are longer – so maybe supervolcanoes are simply composite cone magma systems that simply grow bigger over time. This is not the case because, again the rate of heat delivery rears its ugly head. To grow a supervolcanic chamber requires a much higher (2 to 3 order of magnitude higher) rate of heat delivery to keep the growing volume of magma eruptible. An analogy would be how streams remain flowing in winter….small streams tend to freeze up, while faster flowing larger streams remain unfrozen – the flow rate or discharge is the key. I have dealt with where the heat comes from and why and how the heat flux might vary – that is another story (see later answer to George B). I am talking primarily about what needs to happen in the upper 10km of the crust. So after that long winded explanation, getting back to your original question, yes, silicic and intermediate volcanoes can go through cycles of caldera forming activity if they are subject to changes in the rate that heat is delivered to the magma storage region. If not they are in what is known as a steady-state where they sputter along with small effusive and explosive eruptions. From my perspective supervolcanoes and composite cones or shields are different systems so they are generally unrelated. If of course the heat flux in a volcanic region changed by orders of magnitude you could technically switch from composite cones to supervolcanic systems, but this requires a major change in the plate geometry or crustal structure (see my later answer to George B). If you had to put your money on any area, where would you guess for the next 'super-eruption' to occur? Money and intuition are never a good mix (at least in my case). If I were to speculate I would say that barring any major arrangement of plates any future supervolcanic eruption is most likely to happen where there has already been supervolcanism in the last 5 Ma. Next most likely is where there is active volcanism today, but only if there was some major change in the heat flux – that is why places Uturuncu are interesting. It is a composite cone sitting in the middle of all these supervolcanoes, and the deformation there suggests supervolcanic rates of magma/heat input. Why do the Andes interest you so much compared to other volcanic areas? The Central Andean plateau is one of the most mindblowing landscapes on the planet. You feel like you are on another planet (we use it as analog for Mars) and everywhere you look are volcanoes and volcanic deposits! Millions of years of volcanic history are beautifully preserved waiting to be admired and deciphered. It is a high altitude desert and logistically quite challenging. It is relatively poorly studied, so it is something of an open book, few other groups work there, which has allowed us to really pick and choose some great projects out there. Every place you go to triggers enough questions to fill a lifetime of work for a volcanologist. It is rare to have such a wonderful natural laboratory available.
Alex: With regards to understanding and predicting the time and place of a volcanic eruption: If you could dream up a tool or instrument that currently does not exist, what type of data would you want to collect with that tool and why?
Dr. de Silva: We know a lot about magmatic systems and volcanic eruptions and we are learning more everyday, but there are more unknowns than there are knowns (do I hear Donald Rumsfeld?). The critical questions we still cannot answer today are where, when and how big an eruption will be. Dream instruments would be those that could really address these. Where? – Some people might argue with me on this, but my point is that we are at the point where we can monitor activity at volcanoes once activity develops, but we are still surprised by some eruptions like Chaiten (above), because we don’t have the resources to monitor every possible “volcano”. So we are generally reactive rather than predictive or proactive. A global monitoring system would be great. In my mind this would have to be space based – a satellite system. Current systems exist that can detect thermal anomalies once they develop but are not really effective at prediction and are not really real time. Deformation can also be detected from satellites (interferometric synthetic aperture radar systems) but is not global and not real time and very dependant on a few masterly practitioners. Once activity is detected then we are pretty good at monitoring it and even predicting the course of events to manage risk. The best example is the 1991 eruption of Pinatubo (there is an excellent NOVA production about this eruption). However, I would argue that we are still challenged to predict whether signals of unrest will lead to an eruption, the type of eruption, when that eruption will occur, and how big it will be. We can lean on past activity at a volcano to limit the probable range of type and size of future eruptions, but when and how big remain challenges. How big? – Estimating this requires understanding of how much viable or eruptible magma is available. A dream (and I emphasize this, as it is not realistic with current knowledge) seismic tomography system like VIRGIL in the Discovery Channel movie Supervolcano would be amazing but would need to be portable and deployed at the volcanic hotspot. When? - This is probably the toughest question. Even if we know how much eruptible magma is present, and we could characterize its state, when it might erupt requires knowledge of what might trigger the eruption. This at least requires knowledge of the pressure state of the magma, the evolution and distribution of that pressure and the response of the rocks surrounding the rock to that pressure distribution. All this very dynamic and dream instrument or suite of instruments would have to measure the key variable and integrate all this in real time. VIRGIL remains the closest fantasy instrument I can think of. So in answer to your questions, a global system that can monitor the surface signals in real time would be a major step forward to identifying the next volcanic hotspot. Once the hotspot is identified we need portable VIRGIL’s that can deployed rapidly and broadly to monitor and predict the impending eruption, tempered by a heavy. dose of real geological knowledge about previous activity. But as Jock Galvin in Supervolcano noted VIRGIL is nothing more than a “video game”.
Mark T Burns: How difficult is it to get funding to study and monitor a volcano like Uturuncu?
Volcano monitoring is woefully underfunded. Beyond rare industry sponsored efforts in aviation impacts and geothermal energy, volcano monitoring (and funding) falls under three main funding models (maybe more, but these are the main ones I can think of). 1) International efforts where a few instruments and experts are deployed to a volcanic hotspot (hazardous volcano showing signs of elevated activity) - there is a US based and government funded like the USGS VDAP program. Other international efforts include political and socially challenged situations like Goma in the Congo that are developing but are not as mature. 2) National programs that have developed observatories and programs at hazardous volcanoes – government funded (Iceland, Italy, Japan, US, Indonesia, Philippines, West Indies, Chile etc). 3) Unless a volcano is deemed to be hazardous and threatening to a population or infrastructure there is little direct agency or government funding. So the third funding model is through academic research efforts. These projects range from “SWAT “teams of professors and students that rush out to the latest eruption volcano and do a smash and grab studies, long term multi-year studies of volcanoes like Erebus and Etna, or global remote sensing of volcanism, and occasional really interesting volcanic signals like Uturuncu. Our funding for Uturuncu comes from the National Science Foundation as well as partner funding from the National Environmental Research Council of Britain. We had to compete over a period of two years to get our proposal accepted – success rate for proposal is about 25% Is this a volcano that really needs to be scrutinized immediately or just be aware that it's here? At present what we know is that there is anomalous activity here in an area that we thought was dead. That in itself is intrinsically interesting as actual signals of new activity are rare. The fact that the inferred rate of magma intrusion is as high as required for supervolcanic activity is really interesting as we may for the first time be catching a supervolcanic system in its infancy…or it could lead to nothing…or a small eruption. We just don’t know. The data we will gather over the four years of this project will be a start and will give us a baseline to compare future data to. Where this will go we don’t know, but this volcano should be continued to be monitored. Why the wide range of date given for the last eruption? One you get to a few hundred thousand years the precision of the age dating technique (^40Ar-^39Ar) starts degrading because the amount daughter isotope produced in such a short time is extremely small – more difficult to detect, signal to noise is very low. Additionally Uturuncu lavas do not contain the best minerals to use for the age dating technique. Finally the existing data is quite sparse…more ages allow better resolution. These three factors combine to give imprecise ages for the last eruptions from this volcano. If you could set up an observatory at Uturuncu, what instruments would be a must have? Gas monitoring? Core samples? A mule? If you added a distillery, microbrewery, a hot tub, and good sushi to all of the above and threw in VIRGIL (see above), I’d be a happy camper!
George B: Was there any change in the nature of the inflation after the fairly recent large earthquake in Chile?
Dr. de Silva: With respect to the 27^th February 8.8 mag Maule earthquake, as far as I know no change in deformation has been detected, but Jennifer Jay and the Cornell team have reported in a recent article that seismicity increased: Jay, J.A. et al., 2011. Shallow seismicity, triggered seismicity, and ambient noise tomography at the long-dormant Uturuncu Volcano, Bolivia. Bulletin of Volcanology, in press. DOI:10.1007/s00445-011-0568-7 The seismicity is very shallow – near sea level and therefore much shallower than the inflation source. So it probably related to the changes in the hydrothermal system rather changes in any magma body. I read recently that the volcanism around the area of Uturuncu changed about 1 million years ago and that the area stopped erupting. This would imply to me that there were fairly frequent eruptions in the area until about that time. Are there any ideas floating about which might explain what happened a million years ago that shut down what seems to have been a very active area? Lots of ideas ... I explain above that changes in the magnitude or intensity of volcanic activity can be related to the rate at which heat is delivered to the system. Between 10 and 1 Ma the region was characterized by many large caldera for “supervolcanic” eruptions and since then activity had settled down to steady state composite cone building activity along the chain of volcanoes that forms the crest of the Central Andes. This change signals the rate at which heat was being introduced into the crust changed about a million years ago. What controls the heat influx into the crust? This is very complex, but I will give you the essence without delving too deeply into details – just the facts. Remember that the Andes and it’s magmatism is part of the Ring of Fire produced by convergence of plates. At convergent margins there is a downgoing (subducting) plate and an overriding plate – in this case the downgoing Pacific or Nazca plate and the continent of South America. Heat is advected into the South American plate crust from the mantle in the form of magma primarily and the rate of magma (and therefore heat) being produced is controlled by the rate at which the mantle can melt. The rate at which the mantle melts is related to a variety of factors related to the volume of mantle under the crust that is primed and ready to melt and how that mantle can be induced to melt by causing it to rise (de-pressurising) or adding water to it. These factors are controlled by the geometry of the plates – the angular relationship between the downgoing (subducting) plate and the overriding continental plate. We believe between 10 and 1 Ma years ago the angle of the downgoing plate changed from shallow to steep and this resulted in a rapid increase in the rate at which the mantle was melted and heat was introduced into the crust – think of it as mantle moving upwards into the area opening up between the downgoing and the crust. As it moves upwards the mantle melts and so more heat is being introduced into the crust. Once the downgoing plate settled into its current configuration (steep) about 1 Ma, the flow of mantle ceased and no extra melting occured and a normal heat flux returned – the volcanism settled down to the steady state “dribble” or “sputter” seen today.
Peak VT: Do large emplacements of magma usually erupt? Or, if we cut off the top 10,000 feet of the Andes or a similar mountain range, would we find large blobs solidified magma all over the place?
Dr. de Silva: Ah, another favourite topic. I subscribe to the view that most large volcanic eruptions only erupt a relatively small portion of the entire magma chamber, but there is a lot of debate. The evidence that sways me is that there are strong spatial, temporal, chemical and geophysical similarities between volcanic systems and plutonic suggest that suggest they are complementary. Deeply eroded mountain belts cored by granitic rocks like the Sierra Nevada (above), and the Eastern Cordillera of the Central Andes probably had volcanoes sitting on top of them at one time but have been eroded away.
Angelo: So what happens if this is a supervolcano and it blows up?
Dr. de Silva: We are a long way from knowing what will happen. But “supereruption” scenarios are based on what we have inferred from other such eruptions. Remember we have never witnessed on of these event (thankfully). The Supervolcano movie, in my opinon does a credible job of presenting the impacts. Locally within 100 km, total devastation (but nothing much is there beyond a few small settlements), regional ash fall for 100’s of kilometers north, south and west and 1000’s of km east wreaks socioeconomic paralysis and rapid degeneration of life support and communications infrastructure (days to weeks). Multi-year scale agricultural impact and maybe hemispheric climate perturbation. Most of the impact would be in South America to the east of the volcano but ash in the atmosphere could impact hemispheric and global air traffic and airports. All this is speculation but based on what we know.
Jon Frimann: What are the chance of volcano like Uturuncu to erupt in near future, since it is a old volcano. Iceland has few of this old volcanoes, so it would give me some idea on how they behave when a volcano becomes this old.
Dr. de Silva: The short answer is that we simply don’t know. As I said above just because you have a signal of magmatic activity does not mean there will be an eruption. The age of a volcano is not necessarily a guide for what might happen there. The devastating 1600 eruption of Huaynaputina occurred at the site of volcano that hadn’t erupted in 5 million years! The Chaiten eruption of 2008 occurred in what was considered to be a dormant volcano for thousands of years. If the region is volcanically active then the potential for activity is always there and the location could be any previously active volcano.
Chris Reynolds: What are the odds of a VEI=7 or higher in the next two decades?
Estimating the probability of eruptions of different magnitudes is notoriously difficult to do. It depends on how complete our record of eruptions is and how good a sample we have to work with. A key issue is to know the repeatability of such eruptions through time. Once you get to VEI 7 the sample is extremely small and probabilities are fraught with error. This notwithstanding it is generally accepted that VEI 7 eruptions happen on a 1000 < or < 10,000 year time scale. The only historic VEI 7 we know of is the Tambora eruption of 1815 (although the size is debated). If we take that as the most recent, then the probability of a VEI 7 in the next two decades is vanishingly small. The probability of anything larger is not worth losing sleep over at the moment. Is it possible to make man-made vents to dissipate or control lava flow especially in shield volcanoes? Making man made vents to dissipate or control lava flow (presumably you mean from chamber to surface rather than lava flow on the surface which has been successfully done) is a popular remedy in the blogs and chatter world. Notwithstanding the accidental intersection in Hawaii (very special situation and lucky) it is not very practical and not a good idea to try and bleed off a pressurized magma chamber.
Matt Mabus: Is a lack of the erosional qualities one finds in the Central Oregon Cascades a help or a hindrance in the dating of Central Andean volcanics?
Dr. de Silva: The lack of deep dissection in general can limit going back in time, but allows the geology to be preserved intact. So there is a trade off – on the one hand you may get to sample older rocks inside the volcano, on the other you get a well preserved surface record with great morphological features. Fortunately, gravity and ice can reveal the interiors of some Central Andean volcanoes through sector collapses and glaciation.
Angie Shoaf: Which volcano in this region has given you your most memorable field trip, why, and what did you learn from it?
Dr. de Silva: All the field work in this region is memorable. Favourites will always be my first ever visit to the area in 1983, Sabancaya (Peru) eruptions in the early 1990’s, Huaynaputina (Peru) in the mid to late 90’s where the work was done with mules, working inside the big calderas like La Pacana and Galan. In the last 20 years or so the greatest pleasure has been taking students out to do their research in this remarkable area.
TG McCoy: What is considered a "super eruption" by a shield type system?
Dr. de Silva: The term supereruption is generally used for explosive eruptions which are of higher silica magma. Shield volcanoes are typically basaltic, low silica, and non explosive. However, volcanologist Stephen Self in particular argues that we should consider individual flood basalt eruptions, which can be multiple 1000’s of km^3 in volume, as supereruptions. Of course this is a pure “earthling” perspective. On Jupiter's moon, Io, there maybe explosive eruptions of basalt of supervolcanic proportion. The Medusa Fossae Formation on Mars has been suggested to be ash flow tuffs, most likely basaltic. These would dwarf explosive eruptions on Earth.
GeoLurking: Is there a general upper and lower bounds that the magma 'chamber' forms for "Sortabig" volcanoes?
Dr. de Silva: If you mean is there a limit to dimensions of magma chambers…yes we think there is. At any given depth and shape of chamber there is a limit imposed by the strength of the roof above the magma chamber. As you grow the magma chamber it tends to grow laterally more than vertically. The roof will be progressively thinned – think of a growing bubble on the surface of a thick liquid. Eventually that roof will be extended to the point it would collapse under its own weight thus limiting the size of the magma chamber. Does previous ring faulting tend to promote the piston effect? Previous faults certainly may pre-condition where failure might occur whether it would be as organized as a piston or whether it would be more piecemeal would depend on the integrity of the roof. Is the phenomena generally started from a periphery eruption and then progress/ramps up as the system depressurizes? Yes, this is certainly one mode of failure. Supported by the evidence that the Long Valley caldera “unzipped” during the eruption of the Bishop Tuff, about 740,000 years ago.
Stefan: Regarding the triggers of supervolcanic eruptions: If such an inflated dome was present somewhere at this time, would we able to detect it? Would it be obvious?
Dr. de Silva: If we can deconvolve the “dome” from any regional topography and neotectonics and we can say definitively that the uplift is magmatic then we have a shot at this.
Jill D: Was any uplift noted prior to 20 years ago or was no equipment in place at that time? Do you expect this trend to continue?
Dr. de Silva: We do not know if the signal was there prior to 20 years ago as it was only recognised recently with InSAR. There is no data before then as far as I know. We have tried to use older lakes around Uturuncu to see if they record any tilt (they should be horizontal so any departure from horizontal should be the result of uplift) but those observations have been unsuccessful. It is not possible to predict if the trend will continue.
Me: How much of the inflation/deflation we see at volcanoes likely “business as usual” that we only now notice because we have the technology to do so?
Dr. de Silva: Clearly our ability to detect signals is improving over time. We don’t have enough of a record to know what is “business as usual” but it is quite possible that all these signals are simply background. We need to define that background, so we can identify the anomalous signals. What signs do you think we should expect if a volcanic system was headed towards a large (VEI 7+) eruption in the near future? There is no silver bullet, but we have a toolbox we can use, and we would look for the usual suspects for now until our science . If it is a pre-existing volcano, clear evidence that the thermal structure under the volcano has changed, that magma is accumulating or has accumulated at appropriate rates, yery rapid inflation, other pre-eruption signs like changes in gas chemistry, seismicity, petrological indicators. Why do you suppose that so many people have the impression that we’re seeing more volcanic activity now than in other times in the Earth’s past? I would speculate that we humans are more numerous and more widely distributed and connected than before. Reports of volcanic activity are more efficiently available from a wider area of the planet and are seen by more people faster than ever before. This goes along with the trend for seismicity, number of reports of fireballs (a very interesting trend in the last 6 years) and UFO sightings.
Image 1: Uturuncu in Bolivia. Einalem/Flickr
Image 2: Chaiten erupting in 2008. Macha.cl/Flickr
Image 3: University Peak, California. Feverblue/Flickr
Image 4: Postcard showing an eruption of Sabancaya. Leonora Enking/Flickr
