Two weeks ago I wrote about statistics and the possibility to predict volcanoes in any way by using statistics. I think that the point was a bit lost, my entire point was to show that it was impossible to in any useful manner predict when an eruption would occur, and also that it is impossible to use statistics to show how the volcano will erupt when it does erupt. I also tried to prove that in the end a volcano is more likely to do something statistically unexpected, than the expected.
To accurately forecast a volcano, you are far better off if you study the volcano at question well, and then put a lot of equipment on top of it and then interpret the data. If you are an expert you are quite likely to see if the volcano is about to erupt, and sometimes even say something about how it is likely to erupt.
After that I ventured into Adamsian Improbabilistics and pointed towards it perhaps being a useful tool to say something about eruptions of a particular volcano that is out of the ordinary. The reason for this possibility is that there are so many improbable things that can happen around volcanoes as they erupt that it is interesting to study what is hiding out in the land of improbable.
Albert asked if it would be possible to use Improbabilistics on a particular volcano, Hekla, to see what would could be lurking “out there”. Problem is just that Improbability theory is not yet advanced enough to do that.
So, I thought we should start with looking at a few historical eruptions, just to get a feel for what is improbable (out of the ordinary) around Icelandic volcanoes. After that it is time to look at Hekla from a historic standpoint and see what we can find that is out of the ordinary there.
So, let us take good look at what is hiding among the statistical outliers from the statistical models of our favourite volcanoes. Just to keep it short I will briefly venture out into the 3 last eruptions on Iceland and see if they fall into the statistically probable, or if they indeed where cases that are improbable.
Before the eruption started there had been 3 different episodes of inflation in the volcano. So, it was not unexpected when the final earthquake swarm started that an eruption would follow. In other words, due to instrumentations and interpretation of data the eruption was accurately forecasted, and it is possible that this saved lives.
This is though the end of the good news. Everything else that was expected from statistical analysis was promptly falsified.
The first thing that was falsified was the statistical assumption that this volcano suffers from mild eruptions ranging between a small VEI-2 to a small VEI-3. In the end the eruption turned out to be 10 times more powerful than anything known from historical records.
The next thing that we “knew” about this volcano is that there was supposedly some function that caused nearby Katla to erupt almost directly after Eyjafjallajökull. This sent a lot of doomsayers into playing lip banjo out of joy since Katla would blow the world up.
And, obviously a lot of nothing happened at Katla and it turned out that this mystic connection was just a simple statistic anomaly caused by the normally frequent eruptions of Katla.
Prior to this eruption it was a mantra in volcanology that what comes out of a volcano has entered the same volcano. Or in other words, volcanoes do not swap or inject magma into each other’s magma reservoirs. Even hinting at anything like that was seen as perverse.
In the end we could track 3 individual magma paths from depth. First, we had the known conduit of Eyjafjallajökull itself that had received fresh magma from depth. Secondly, we had a completely unknown conduit that went up to Fimmvörduhals (where the initial eruption started), that conduit later took a sideways walk and connected with the one at Eyjafjallajökull. The third conduit is the one reaching up to Godabunga. There are haunting trails of earthquakes reaching from Godabunga towards Fimmvörduhals prior and during the eruption there. As such Fimmvörduhals could have been the first eruption of Godabunga.
In other words, even though this eruption was expected from seismic data over two decades, it turned out to be a fairly improbable.
If we fast-forward a year we get to the largest explosive eruption since Cerro Hudson vent boom in august of 1991. In 1996 Grimsvötn had thrown us a true black swan as an earthquake at Bárdarbunga set off a radial fissure eruption of Grimsvötn at Gjálp.
Before the VEI-3 of Gjálp it had mainly produced numerous weak eruptions for more than a century. Gjálp at VEI-3 was the largest since 1873 (minor VEI-4), it was also producing quite a bit of lava. This lead most people to believe that the next eruption would take a while or, be a regular small VEI-2.
But, alas, as soon as 1998 came another VEI-3, this time at the south caldera wall. And once more statistics came into play and everyone said that it would either take time to the next eruption, or it would be a VEI-2. Rinse repeat in 2004.
By now people had come to the conclusion that Grimsvötns pattern had changed a bit and that VEI-3s a few years apart might be the new thing for the volcano.
As earthquakes picked up in late 2010 everyone was expecting a mild VEI-3 to follow. Instead we got ashmageddon and an eruption that was an inch of a VEI-5. Another way to put it, the eruption turned out to be about 80 times bigger than expected.
Once more it was back to basic research. In the following years we understood that the deep reservoir of Grimsvötn had been depleted during Lakí in 1783, and that it was not until now that it had been fully replenished.
We also learned that Grimsvötn has 3 different shallow magma chambers, and that all of them had been almost completely destroyed in a series of VEI-6 eruptions known as the Saksunarvatn tephra’s.
If we had known all of that in 2011 we would not have been as surprised. But back then it was seen as a full on black swan, but in reality, it was just our ordinary day improbable grey swan.
In 2014 we got a true black swan as a large amount of magma entered the relatively unknown volcano of Kistufell. Such intrusions are not uncommon in Iceland, most often nothing happens, and the magma just remain in the magma chamber.
This time there was just too much of it, so it first tried to hammer its way straight up, but the lid was stronger than the side of the chamber and the magma started to move towards Bárdarbunga and succeeded with entering that magma chamber.
Once more the lid was stronger than the sides of the magma chamber and the magma from two volcanoes started to progress towards the fissure swarm of Grimsvötn. As the magma arrived there it rebounded against yet another volcanic intrusion hotspot that we have named Greip. It has been suggested that the magma flow here connected with the magma conduits of Greip and that the flow was now powered by 3 separate deep conduits in a perfect threesome of magma-swapping.
The magma then travelled up to a previous eruptive zone known as Holuhraun where it popped up in a rather massive way. Incidentally every text book before 2014 said that Holuhraun was erupted in 1797 by Askja, not Bárdarbunga. Well, we learn something new every day.
It is not that Bárdarbunga erupted that is a black swan, and it is not the size. Bárdarbunga has produced far larger eruptions in it’s lifetime. What comprised a black swan here was that prior to the eruption we did not know that different volcanoes could play magmatic snooker with each other exchanging wads of magma with each other and bouncing that magma around a sizeable portion of Iceland. Seems that we did not learn the lesson from Eyjafjallajökull that well.
Conclusion so far
The only conclusion we can draw with such a small sample of eruptions is that improbable eruptions seems to occur improbably often. We could probably make a list of how big a percentage of Icelandic eruptions are unexpected and improbable in one way or another, but I think we will find that it is more common with the uncommon than we expected.
And now it is time for the mother-factory of black swans. The swaniest and blackest of them all.
It was an improbably nice Icelandic morning in May 5152BC as a bowl of petunias materialized on the plains northwest of Hella. It looked around and said to itself; “Oh no, not again!”.
Quickly a series of powerful earthquakes ripped open a 6.5 kilometres long fissure at a with of about 50 metres. Out of the fissure roared ash and pumice towards the sky as the bowl of petunias was shattered.
Within an hour or two 5 cubic kilometres of ash, pumice and tephra was ejected. After that, as if someone had pushed a button, the eruption changed, and 1200-metre-high lava fountains fountained out along the length of the fissure.
After a couple of weeks, the eruption was over, leaving a fresh plain of still molten lava. The only remnants were a series of low spatter cones left behind. Hekla had been born unto us.
Compared to any other volcano, and the birth of any other volcano, this was the black swan of all volcanic births. The paradigm of volcanoes is that they are born relatively calmly with frequent small eruptions as they are young, and that as they mature they will have fewer eruptions that are larger due to the development of their magma reservoirs. Hekla did it in reverse order.
Hekla then continued to have large (VEI-5) eruptions far apart in 4700BC, 4110BC, 2310BC, 1550BC, 1100BC and 1104AD. Seven eruptions in 6000 years might not seem a lot, but if all of them follow the brutal pattern of Hekla, it will still construct a mountain.
We do know that Hekla looked different prior to the 1104 Seslund Pumice, and also that it was significantly lower compared to today. The eruptions up to and including 1104 was just to brutal to be good at constructing a majestic edifice.
In this series of 7 eruptions only 2 can be seen as black swans. The first one is obviously one. The second one is also one since large fissure eruptions rarely happen at the same place. Iceland is filled with one hit wonders that have left a fissure row behind as it’s only legacy.
After 1104 something changed, and we do not know what. The style of the eruptions stayed the same with an initial short brutally explosive phase, followed by lava pouring out. After 1104 Hekla erupted roughly every 50 years six times in a row, ranging from VEI-2 to VEI-4.
Then it calmed down and started to pace itself slightly better with inter-eruptive periods ranging from 50 to 150 years. These can be called the classical years of Hekla. It had by now a tremendous reputation as the gateway to hell.
But, once more Hekla felt the need to change things, and in 1947 it started the modern age of Hekla with far more frequent eruptions ranging between 1 and 27 years. The eruptions once again diminished in size a bit.
In a sense of it Hekla is becoming younger as it is aging. It started big, and then as time went by it started to erupt more often and smaller instead of going the other way.
In a way Hekla is that Rockstar that everyone loves, a volcanic badgirl. Living life to hard, using to much drugs, and we just know it will end badly and after a short lifespan.
Question is more how Hekla will end. Will it erupt so often and so hard that in the end the edifice becomes to heavy and it all drops down and form a caldera. Will it sputter out, forgotten on a wayside roadhouse of volcanic music drowning in its own vomit. Or, will it go dormant and make a comeback in a thousand years with a final cataclysmic VEI-6 concert that kills it on stage?
Personally, I favour the version where the edifice becomes to heavy and it drops down into the wedge-shaped magma reservoir under it as a flood of lava pours out to cover any trace that this improbable volcano ever existed.
In the end, the only true black swan left in regards of Hekla is if another Hekla happens. Today it is unique, so much so that it is a class of volcanoes unlike any other on the planet. And it is a class of one. As such, another would be the true black swan. And since it is so improbable it will probably happen quite soon.