This week there are three volcanoes worthy of attention. So, I thought I would write a brief update on them since we have covered them either recently, or in detail. Without further ramblings let us go on to Gunung Agung.
And as I came to my final and third volcano life coughed up a fourth volcano doing something unexpected and I had to rewrite the end, but more about that below.
Since I last wrote about Agung the plug has cracked and highly viscous lava have started to extrude out of the vent. Around it we can see steam coming out, but there is by now far less tephra, even though there are intermittent blasts of it.
Seismicity remains high, but at a lower level than prior to the onset of eruption. The tremor and types of earthquakes are typical for a volcano that is charging for an eruption, and it is almost certain that a more powerful phase will come in the end.
So far, the eruption of Gunung Agung is following the historical pattern from 1963. If that patterns hold true we should be seeing a more intense phase in the latter half of December. But, it could in all fairness happen at any time.
What amazes me is that such a large number of tourists are taking very complicated selfies of themselves close to the volcano. They are posting detailed pictures of them doing anything from yoga, to dancing tango, in front of Agung.
Some of them also make rude remarks about the locals fleeing the volcano, writing things like “it is only puffing” and some such. Well, if the locals are evacuating it is due to the not so small fact that the local scientists and authorities darned well know what they are doing.
So far, the monitoring and mitigation have been done in a beautiful style, and there is no reason to assume that it will not be done so in the future. So, if you are a tourist in the area, recognize that this is a potentially deadly event and that the volcano can indeed kill you if you do not follow instructions.
It is easy to become overly excited when you read that the volcano of Öraefajökull has had its largest recorded number of earthquakes, or that a magmatic intrusion has occurred at a depth of 6 kilometres, or that hydrothermal vents have started to melt a large cauldron in the glacier covering the caldera.
To put this into perspective we must though remember that Icelandic volcanoes typically suffers up to ten thousand earthquakes prior to an eruption, or even more. So, on the earthquake count this is not much more than a “hello, I am alive” call.
The same goes for the intrusion. This one is small by Icelandic standards, for instance it is far smaller than the final Eyjafjallajökull intrusion (there was at least three intrusions). Currently to little magma has risen to be able to cause an eruption on the scale that we do know that Öraefajökull most often suffers.
And in regards of the hydrothermal melting of the glacier. So far a round disk a few hundred meters across has melted down to a depth of between 25 to 30 meters. This should be put into perspective that the caldera is a bit more than 4 kilometres across and that it is about 500 meters deep.
What is though new in the news is that the cauldron is still growing, and that it has taken on a more drop like shape extending towards the glacial outflow area. This is quite natural since the ice would become less viscous as it heats up, and that it would be starting to flow more easily out of the caldera. This causes a bit of a risk for those who are close to the glacial outflow area. It also means that there is a slightly larger risk that a jökulhlaup will occur.
Even though Öraefajökull is still a bit of a chill pill, I am quite convinced that it will erupt within the next decade or so. That assumption is based both on known historic behaviour prior to onset of previous eruptions, and also on the slowly escalating signals that the volcano is putting forth. As with any volcano in Iceland, activity can ramp up quickly. But, it is not until you start seeing that tell-tale large earthquake swarm that an eruption is around the corner.
But, when it erupts I full on expect to see a Red bull-sponsored video of someone paragliding into the towering ash column, never to be seen again.
Hekla has a reputation of being the ultimate Viking volcano. It wakes up, have a mead breakfast, and go full on berserker while barfing all over the place. According to instrumental records from the last few eruptions this indeed seems to be the case. You have a brief minor earthquake swarm lasting between 32 to 90 minutes and off she goes.
It has though been my opinion that Hekla has the same precursor activity as other volcanoes, just that they are quite quieter than your average run of the mill volcano.
During the last 6 years the Icelandic Met Office have diligently been upgrading the network around Hekla. They have replaced old seismometers with brand new ones, and they have also expanded the network substantially.
There is even a dedicated seismometer called Fedgar and a GPS called Heklukriki that are so close to the volcano that it is unlikely that they will survive onset of an eruption. Fedgar together with the new Mjoaskard seismometer are there to hunt these elusive precursors that might be coming out of Hekla. The third new station is called Hestaalda.
All of these improvements, extensions and closer placed seismometers has created a network that is more than ten thousand times more sensitive than the network during the year 2000 eruption.
And then the long waiting started as Hekla showed nothing suspicious. Until three days ago when Hekla had a small swarm of earthquakes. None of the earthquakes was out of the ordinary. It is what happened that was so small that it was not possible to locate them as discrete earthquakes that is exciting.
All of sudden there was small signals detected that looks quite like what we see prior to an eruption at volcanoes all around the world. We see them at Öraefajökull, and we see them in far off Gunung Agung. And now we have seen them at Hekla.
Are these signs of an eruption coming closer? Well, thing is that we do not know for sure. We just simply do not have a record of anything similar at Hekla. It will most likely be only in hindsight after the next eruption that we can pinpoint what are the precursors of Hekla, or not.
What we do know and can compare is the number of earthquakes above M0.8 with what happened prior to the 2000 eruption. And we can see a pattern where these larger earthquakes have increased a lot over the last few years. And that we do know was also the case in the last few years of the previous millennium.
Skjaldbreiður is Iceland’s largest shield volcano. It erupted about 9 000 years ago in an eruption that took about 100 years. During that eruption roughly 50 cubic kilometres of lava was erupted. The lava flows reach all the way down to Thingvellir.
The volcano is believed to be a part of the Prestahnúkur volcano. But that is not ascertained since Prestahnúkur is a rhyolitic volcano and Skjaldbreiður was a pure basalt eruption.
Skjaldbreiður lies across the Western Rift Zone in Iceland and has been torn and twisted due to seismic forces during the last 9 000 years. But, as with any other volcanic feature in Iceland it is often hard to see if an earthquake swarm is volcanic or tectonic.
In this case it seems to have started off as a tectonic swarm. But the location is where there presumably would be a residual magma reservoir after the large eruption. The earthquake swarm is also directly below the main crater.
One possibility would be that this is neither a tectonic, nor a volcanic, earthquake swarm. It could also be induced by crustal deformation stress caused by the weight of Skjaldbreiður pressing down the continental crust.
Another explanation could be that this is caused by old magma that is shrinking due to heat loss, perhaps in combination with crustal deformation.
It is though good to remember that magma is never far off in Iceland, and large tectonic swarms tend to turn into dyke intrusions over time. If that happened it would though not be a sign of an impending eruption, it would just be Iceland doing what Iceland is all about. And that is transporting magma into the crustal layer.
An if not, we would still need to wait for that ten thousand earthquake rich swarm before an eruption would indeed happen, and we are not even remotely close to that yet.