Irpsit
July 9, 2014 at 00:33
I posted this too quickly, and I want to detail more on what I said.
Let’s keep to facts, as islander said.
Katla has had medium sized eruptions, explosive and quite ashy but nothing out of the ordinary for Icelandic standards, roughly once or twice a century (these are VEI4, about the size of Grimsvotn 2011 eruption or 2010 Eyjafjallajokull eruption). Every few centuries Katla might do a bit larger VEI5, which can be very ashy and large glacial floods. Not a disaster, but quite ashy when one reads the historical reports or follows the tephra layers across Iceland.
Very rarely, perhaps even few dozen thousand years, Katla has caldera forming eruptions. Last one being about 10.000 years ago (Vedde Ash). We simply know little about such mode of eruptions. I reckon, like Carl says, that there is a crescendo of larger eruptions, until a very large one, probably after a longer period of dormancy. Although unlikely, it’snot impossible. But I would find it more likely to see a caldera event in the new centuries in Hekla or Grimsvotn rather than another one in Katla (first Hekla never had one, second Grimsvotn had some of its greatest eruptions in recent millenia just in the last few centuries).
So, accordingly to historical patterns, and this is just an estimate (note that volcanoes often break with the patterns), Katla should likely erupt sometime this century, and judging by its crescent restlessness in last decades and especially last few years, one would be confident to say it would be more likely to erupt earlier this century. When we don’t know? It could be this September as it could be only by 2030.
Obviously it’s not out of the question an eruption this autumn. Why? In 2011 Katla had probably a minor VEI1 or VEI2 eruption, (we had no way of confirming it, since an eruption that size would never break through the ice cap). And Katla had such an eruption just 1-2 months following a period of increased seismic activity, which started pretty much like it is happening now, severa swarms, gradually showing up a few M3 earthquakes. So, if we have such a crescendo now, we could likely expect a similar event, at least identical to 2011. We don’t know how noisy it would be if Katla would be to have a VEI4 or VEI5 event. Eyjafjallajokull was certainly seismically restless just before the 2010 VEI4 event, certainly a lot of swarms which started suddently 3 months before the eruption, but it had no big earthquakes. Katla could behave similarly. That is not out of the question. Remember that Grimsvotn a massive caldera eruption (the first within the caldera since 1938) without much of a fuss, in terms of earthquakes. Katla would behave similarly. However I do think, judging in the 2011 events, that Katla is more noisy and would probably have several M3 or even M4 quake swarms just before a VEI4/5 eruption.
Which other facts we know? GPS-wise Katla has been gradually inflating, at a constant basis, over the years, but there is no sudden GPS inflation. While Eyjafjallajokull had sudden GPS inflation prior to its 2010 eruption, Grimsvotn only inflates gradually until a certain ammount before it erupts. We do not know what mode would Katla follow. Again, here, it’s not out of the question that Katla could behave similarly to Grimsvotn.
Of course we should not fall in doomy scenarios. We also know little regarding this. And I am certainly not a expert. I just follow the pieces of information. There is nothing at the moment to suggest Katla will erupt, but the volcano is becoming a bit more restless, just like it was in 2011, but not yet at the same levels. And remember that the 2011 activity did not result in anything significant.
On a personal level, I have noticed changes in Katla in the last few years, from my hiking experience around the region (but I only am in Iceland since 2009). Some rivers have shown sulphur smell after years of not having them (remembered the river leading to Ermstur on the west side of the ice cap). The 2011 had some major impacts in the ice cap, and of course the flood that followed. Last time I was camping near Katla, I also had the impression (but this is highly non-scientific), that the entire region (of Myrdalsjokull) is near an eruption I dreamt about it and it was a gut feeling. But obviously this is even more speculation, than my scientific talk before, which was also mostly speculation. With all this in my mind, I am not worried about any eruption in soon, maybe in a few months, but most likely in the next couple of years. This is just by speculative bet.
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