Archive for May 2012

Quetrupillán – the headless ghost   Leave a comment

There is a legend of three volcanoes in Chile. They form a line, with the tall and proud ice-capped peak of Lanín volcano at one end, and the gently smoking, demure, and shapely ice-capped volcano of Villarrica at the other end. In between the two is the stunted Quetrupillán, and which has a somewhat beheaded look about it. As if someone has removed the top of a once proud peak.

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Lanín volcano (3,747 m high). The proud warrior….

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Villarrica volcano. The demure and smoking lady….

The legend is that Lanín was a proud warrior who loved to gaze upon his lovely smoking lady of Villarrica. But growing between them was a warrior called Quetrupillán, and as Quetrupillán grew larger Lanín became frustrated that his view of the lovely Villarrica was becoming blocked. Frustration grew into anger and in his rage Lanín cut off the head of Quetrupillán.

Quetrupillán means ‘the headless ghost’ and this could be either a quaint story invented by indigenous tribes to explain to their children why these three volcanoes have different shapes, or perhaps it is a story passed down through time by ancestors who witnessed the eruption at Quetrupillán that destroyed the summit cone.

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Quetrupillán volcano, showing the ice-filled summit crater with remnants of the original cone flanking the ice.

This is something myself and my Chilean colleague are investigating. Actually we are investigating quite a lot about Quetrupillán. But for now I’ll say a little about the trip we did back in March of this year (2012).

Quetrupillán has a famous neighbour – the smoking volcano of Villarrica. It is understandably famous because the ‘smoke’ is a noxious cocktail of magmatic gases escaping from an active lava lake that occupies the summit crater. And because it’s a fairly easy hike up to the summit to look down into the lava lake. Everyone who goes up there comes away moved if not awed by the volcano, as for most this is a truly unique and weird experience. But turn away from the summit and gaze around and the eye is drawn to the superb ice-capped volcano of Lanín, which lies on the border of Chile and Argentina. (In fact the border goes over the summit.) Lanín looks higher and in fact it is, because it sits on a separate (higher) crustal block, but this is not the place to delve into the vagaries of basement geology and discriminating between the little that is known and the large that is speculation.

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Lanín in the background, with ‘beheaded’ Quetrupillán in the middle ground. Taken from the summit of Villarrica. Volcanologist colleague is wearing mask due to noxious magmatic gases escaping from the summit lava lake. Photo courtesy of Jose-Luis Palma.

Looking down from the rim of Villarrica into the lava lake. Taken in 2004, the level of the lava lake is quite low, so only occasional splashes of glowing lava were seen.

Few pay any attention to the less obvious and shorter volcano that lies between Lanín and Villarrica. But this is a rather special volcano. This is Quetrupillán.

My Chilean colleague Andres knew of my work on Icelandic volcano-ice interactions, and that I had worked on another Chilean volcano. So he asked me to go on a recce to Quetrupillán to see if there were interesting volcano-ice interactions.

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The author on his trusty steed. There is no vehicle access to Quetrupillán, so the choice for those who cannot afford a helicopter is either horseback or walking. Photo courtesy of Beth McGarvie.

Riding on horseback through forests of Araucaria Araucana was rather special, as the trees exude an enduring and timeless air. The wreaths of cloud added to the feelings of otherworldliness. Photo courtesy of Beth McGarvie.

Now I’m not going to give too much away as there’s a grant proposal being written to do further research in this fabulous place! So I’m going to restrict myself to leaving you to enjoy a few images that reveal some of Quetrupillán’s beauty, and hopefully the captions accompanying the images below will say what needs to be said.

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Imagination time. Imagine a lava flow creeping slowly through a circular tunnel tunnel melted into the ice. Cool down the lava flow, then remove the ice. This is what we have here. The giveaway evidence is the radial columnar joints (indicating cooling against ice walls and ice roof) and the sinuous shape of the lava flow showing that it was confined (by ice).

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Laguna Azul lies south of Quetrupillán’s summit, and our camp was in the woods. The twin peaked volcano in the distance in Volcan Mocho-Choshuenco.

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One for the the volcanology geeks. These top-bottom ridges on this chunk of dacite lava column represent staggered cooling of the lava, as columns don’t form smoothly – they form in increments or steps. The fracture pattern on the surface (when preserved, as here) indicates development of the fracture from solid into ductile (hot) lava, and so gives the direction in which the column was forming. In this case from left to right.

Lanín in the background, with one of the young dacite lava flows from Quetrupillán damming the outflow of Laguna Azul.

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Laguna Blanca on the south side of Quetrupillán is fed by glacial streams and so has a milky appearance. In the backround is one of the young (Holocene) andesite lavas from Quetrupillán. The pale-coloured block is an example of ‘peperite’ where a lava has flowed over wet unconsolidated sediment and steam action during lava-sediment interactions has aided mixing between the two components.

Torfajökull – waiting in the shadows   2 comments

In this post I’m going to say something about a volcano that has not yet featured in the popular lists of ‘future Icelandic volcanoes that may erupt’. It is a volcano that is close to Katla and Eyjafjallajökull, if not quite in their shadows.

But I’ll start with my view of Eyjafjallajökull as this woke the world up to Iceland’s volcanoes, plus it provides a nice link to one of the points I wish to make.

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Eyjafjallajökull – where the flood escaped during the April 2010 eruption. Taken in August 2011.

The 2010 Eyjafjallajökull eruptions (remember there were two?) surprised us in three ways. First, the tricksy way in which the magmas uprising in March did a sudden detour to the East and erupted in the saddle between Eyjafjallajökull and Mýrdalsjökull. The seismic pattern had us all predicting a summit eruption, and then we got a beautiful and unexpected side-step. Neat. Second was the uncanny ‘perfect storm’ that made the April summit eruption so significant: an unusually efficient magma fragmentation process in the vent that produced a high proportion of fine ash capable of being transported long distances; an unusually long duration of c.45 days for such a small volume eruption; winds that took the ash direct to the UK and western Europe, and that persisted; a lamentable lack of preparedness by UK and western European governments and regulatory bodies for ash in the air; too much emphasis placed on imperfect models of atmospheric ash concentration; and insufficient ‘hard’ and real-time evidence gathered of actual ash concentrations over Europe during the eruption. All of which led to the infamous ‘no fly’ chaos. The third one is that nobody thought this volcano could produce such an eruption, as historical records showed that no eruption like this had occurred since Iceland had been settled by Nordic tribes (i.e. the preceding 1136 years, assuming a settlement date of 874 AD). Which leads neatly into the point I wish to develop….

Which is that although historical records in Iceland are pretty impressive there are omissions and inaccuracies, but the important point is that historical records cover only the past 1138 years, which is not even the blink of an eye for some volcanoes. Add to this the fact that only a few Icelandic volcanoes are sufficiently well studied that their entire Holocene volcanic histories are known with some confidence. (Quick note that the Holocene refers to the current ice-free period – i.e. interglacial – that covers the past c.9,000 years. Even more telling is that remarkably little is known about the volcanic history of any Icelandic volcano prior to the Holocene. Why is this important? Well, given that Icelandic volcanic systems are considered to have life-spans of 0.5-1.0 million years, a mere 1138 years of historical records cannot provide a representative perspective of the longer-term eruptive activity of a long-lived volcano. Even if the Holocene history of a volcano is well known that’s still just c.9,000 years we know about, which is a mere 2% of the life-span of a 0.5 million year-old volcano.

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c.1480 AD rhyolite lava at Torfajökull (the darker lava). Brighter and paler colours are older and hydrthermally altered rhyolite.

So what about Torfajökull?

It has impressive credentials, the most prominent being that it is Iceland’s largest active rhyolite volcano. And rhyolite is the type of magma that is so viscous (sticky) that it is most easily blasted into small fragments (ash) during explosive eruptions. This is one of the very few Icelandic volcanoes for which we have reasonably accurate ages for any of its pre-Holocene eruptions, and this led to an exciting discovery which is revealed at the end of the next paragraph.

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Basaltic maar near Torfajökull produced during the c.1480 AD eruption.

Let’s start with the most recent eruption, which took place c.1480 AD when two small rhyolite lava flows effused (accompanied by only minor explosivity) on a linear fissure that to its NE erupted a substantial amount of basalt. There were a further c.9 other eruptions like this earlier in the Holocene, but before you think there’s a decent pattern here, step back into the glacial period just before the Holocene (the Pleistocene) and prepare for a surprise. Around 70,000 years ago when the area was covered by at least 500 m of ice a ‘ring fracture’ opened up around the margins of the volcano and out poured c.16 cubic kilometres of rhyolite. This was hypothesized as Iceland’s largest known rhyolite eruption back in 1984 (by me), but until the ages had been determined we didn’t know when it took place.

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One of the c.70,000 year old rhyolites produced during the ‘ring fracture’ eruption at Torfajökull. This is Kirkjufell.

There is evidence that the rhyolite erupting 70,000 years ago pierced the overlying ice during explosive activity and spread ash far and wide, as a 5.5 cm thick ash layer in the Norwegian Sea has been attributed to this eruption. This is an enormous thickness by the way, as the Eyjafjallajökull 2010 ash layer at the same location won’t even be 5 mm thick.

At the moment at Torfajökull you can bask in hot pools beneath one of the 1480 AD rhyolite lava flows, blissfully unaware that minor amounts of magma are on the move beneath you (indicated by occasional earthquake swarms of a specific type). And that beneath the western part of the volcano a small magma chamber has been ‘imaged’ using patterns of seismicity. The potential ‘mush’ zone – an important birthplace of rhyolite magma – is likely to be much larger than this, but is notoriously difficult to detect and ‘image’. But it will be there.

Conclusion? The next eruption at Torfajökull is likely to be similar to the other Holocene eruptions, so expect a small rhyolite fissure eruption triggered by a basaltic fissure eruption to the NE of Torfajökull. However if the rhyolite that erupts happens to be loaded with volatiles (gas) then a decent amount of ash will be produced as the gas expands like crazy during its rush to the surface and in doing so fragments the uprising magma into ash-sized fragments. And there is some research I’m involved in that is showing that Icelandic rhyolites contain more gas than previously thought, thus enhancing the potential for greater explosivity and greater ash production, the combination of which could put enough ash into the atmosphere to merit diverting flights. But that’s another story….

Undereath this geothermal field lies the ‘imaged’ small magma chamber.

The links below will take you to papers dealing with:

Dating the c.70,000 year old and other eruptions at Torfajökull

Volatiles in one Torfajökull eruption

Explosive rhyolite eruptions beneath Icelandic glaciers

Rhyolite volcano-ice interactions in Iceland

Ice melting and potential effects on eruptions

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https://docs.google.com/open?id=0B9nifcNoPqF3TEs5QUNPYnFQYkU

https://docs.google.com/open?id=0B9nifcNoPqF3ZVJZRnZsYmZIMDg

https://docs.google.com/open?id=0B9nifcNoPqF3Q1JKVDRoazczX0E

https://docs.google.com/open?id=0B9nifcNoPqF3SURyeWZOeGd3MEU

https://docs.google.com/open?id=0B9nifcNoPqF3R01EaXRFSURFNDQ

Posted May 18, 2012 by davemcgarvie in Uncategorized

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Earthquakes in Iceland during April 2012 – Part 1   1 comment

Well there were c.1300 earthquakes in Iceland during April 2012. If you want to know more, read on dear reader….

Every month the Iceland Meteorological Office (IMO) publishes a brief report (see http://www.vedur.is/um-vi/frettir/nr/2484), so what’s below is extracted from this and supplemented with my own comments and views. The image below is taken from the report and copyright resides with Veðurstofa Íslands (IMO).

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Human-induced earthquakes.

Around 500 of the earthquakes occurred in and around the newish geothermal power station (Hellisheiði) that lies to the East of the capital Reykjavík, and which supplies the capital with hot water etc. These earthquakes are caused when cold water is pumped back deep into the geothermal field, which is necessary to replenish the hot water and steam that is extracted. It’s actually a rather neat way of accelerating the natural cycling that takes place anyway in such geothermal systems. And sustainable, until the heat source diminishes. The earthquakes are triggered by ‘thermal cracking’ and the movement of small faults and fractures which are lubricated by the incoming fluids. Some of the earthquakes have been a tad large (M3.5) which has shaken the residents in the nearby town of Hveragerði who are naturally anxious because they were deeply affected by the May 2008 M6.3 earthquake. But most are fortunately small and cause just a modest tremble.

Katla (also known as Mýrdalsjökull, as ‘jökull’ means glacier, and a glacier covers Katla).

Well it would take me a few pages to tell what I think of Katla, and what I know about her. But the period of seismic unrest that kicked off in July 2011 with the modest but significant bridge-busting glacial outburst flood, tailed off towards the end of 2011 but continued through to March 2012. Arguably it is still continuing, albeit in a diminshed and more fluctuating form. See  http://www.geos.ed.ac.uk/research/geohazard/KatlaEQ.html

But Katla is still ticking over, with 135 earthquakes in April, and with another small flood that did no damage but merely pointed to the sudden release of a pulse of meltwater – most likely either a body of water had been accumulating for while and that was stored in a specific location before being released, or a sudden burst of thermal energy from the bedrock that rapidly melted ice at the glacier base and which escaped immediately. No one knows which, as instrumentation cannot resolve at the scale necessary to indicate exactly what is going on under 400-700 m of ice.

In my opinion Katla is currently ticking over like an idling car. And although she is as carefully monitored as she can be (and the Icelanders are excellent at this, as proven during the 2010 Eyjafjallajökull eruptions). Past substantial eruptions, like 1918, are preceded by large earthquakes. So it would be very surprising if there was a large eruption without precursory large earthquakes again. For now, there is nothing to suggest that Katla is preparing for a substantial eruption. But this is not an exact Science, so surprises can happen!

In Part 2 I’ll say a bit about earthquakes elsewhere in Iceland and how these link to large scale structures such as the transform fault systems. And on the interesting earthquake swarm that’s currently occurring west of the spectacular subglacial basaltic table mountain of Herðubreið. Of which I attach a picture taken from the Askja volcano, below.

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Posted May 17, 2012 by davemcgarvie in Uncategorized