The Unusual Suspects

With the current eruption at Eyjafjallajökull rumbling on relatively steadily, producing an ash cloud that continues to wreak havoc with European air traffic (at least when this article was written), I thought it may be interesting to take a look at some other potential troublemakers living on this island.  After all, Iceland is a land formed almost entirely by volcanic processes, and there is on average an eruption every 3 to 4 years—there’s hardly a shortage of potentially active volcanoes.

Trusty ol’ Hekla

First in our line-up is Hekla, the infamous Icelandic ‘gateway to Hell’. Beautifully conical from one side and similar in appearance to an upturned boat from the other, with a penchant for producing spectacular fire fountaining fissure eruptions, Hekla is a magnificent looking mountain. But it has produced some quite large explosive eruptions—in particular 1104 AD, and more recently a smaller but no less spectacular eruption in 1947.

Since 1970, Hekla seems to have settled into a pattern—quite an oddity in volcanology, a science where nothing is ever predictable—and has produced a relatively small eruption almost exactly every 10 years. The last of those was in 2000. On its own, this would be less than convincing, but measurements show that pressure within the mountain is currently higher than prior to the 2000 or 1991 eruptions. You could really consider Hekla primed to blow. It’s also an odd beast because it produces no real earthquake activity until immediately (an hour or so) prior to an eruption, so when we see the ground shaking here, we know something is up.

Grímsvötn builds pressure

Our next suspect is Grímsvötn, a well-hidden volcano whose favourite tool of destruction is the jökulhlaup (glacial outburst flood). Buried below the enormous Vatnajökull ice cap, Grímsvötn is unlikely to mess with air traffic any time soon because all that ice will probably stop much ash from escaping very far, but such sub-glacial eruptions have a history of aggression against bridges and other structures.

Grímsvötn’s crater contains a lake lying beneath the ice, made of water melted by natural geothermal heat. Unlike most volcanoes, which may produce a jökulhlaup due to ice melting during the eruption, it’s thought that this lake can naturally overflow, and this release of pressure can trigger an eruption. Whether the jökulhlaup comes before or after the eruption, though, they can often be pretty damn big. And right now? Well, as with Hekla the internal pressure is pretty much at pre-eruption levels, and the sub-glacial lake is also approaching its maximum height. You might only see an eruption here on the news, due to its remote location, but it should still be quite a spectacle.

Biblical Katla

Our last volcano of interest is the one everyone seems so worried about at the moment —the legendary Keyser Söze of Icelandic mountains, Katla. Katla sits right next to Eyjafjallajökull, is much bigger, and history shows that it probably has some kind of linkage to its neighbour—the last three times Eyjafjallajökull erupted, Katla followed suit within a couple of years. With a general historical trend of 1–2 eruptions per century, and the last confirmed (and quite sizeable) eruption in 1918, you could argue that we’re ‘overdue’ a Katla eruption. The volcano itself is capable of producing all sorts of dangers. The enormous 934 AD Eldgjá fissure eruption originated from the Katla volcanic system, and the 1918 eruption produced both an enormous eruption plume (which in today’s world could have a major impact on air traffic) and an unimaginably huge jökulhlaup, which washed icebergs the size of houses down onto the plains below.

So what’s the current state of affairs? Who’s the prime suspect for our next volcanic crime? Frankly, I think it’s unlikely to be Katla. I don’t think anyone is denying that Katla needs to be kept under close watch, but right now it’s showing little sign of stirring as a result of the Eyjafjallajökull eruption. Hekla and Grímsvötn, on the other hand, are both showing signs of more or less being ‘ready’ to go. Chances are that neither of them is going to be particularly dangerous (unless you’re right on top of them!), but my money says that one of them will be our next guilty party…