A little while ago there was a short interview published with Professor in geophysics, Páll Einarsson. In the interview it seemed like he was stating that Bárdarbunga, Grimsvötn, Hekla and Katla all were preparing to erupt shortly.
First of all let me state that I deeply respect Páll as a geophysicist, problem is just that he is probably the most misquoted and misinterpreted scientist on the planet. The problem is that he is talking about geological timeframes and he uses words like “shortly” and “soon” in that context and then the journalist happily thinks he is talking about the next few weeks…
So, once more it is time to take a look at the instrumental evidence at hand and write about the probable eruptive timelines in a slightly more understandable way for the lay audience compared to the sweeping broad geological sense, or the hysterical short time span of journalists.
Or in other words, let us put a human timeframe on geological timescales in alphabetical order.
A bit about changes at Volcanocafé
Volcanocafé has so far mainly been a popular science magazine where the readers can interact and discuss all things volcanic (and quite a few other things). This will always be the case, but things need to evolve to not become stale.
Lately the technical wizards behind the scene have been doing really weird things with the intent of making the place far more interactive. I will not state what the end of it will be since I barely understand it. So it is up to them to make the announcements when they are ready. Let us just state that there will be things and tools coming that will be really useful during the upcoming year, especially for those who are friends of Icelandic volcanism.
And before I start I would like to thank Andrej Flis (DownUnder) for the wonderful 3D-videos of earthquakes that is the graphical backdrop for this article. Look through them and while doing so I urge you to think about the volcanoes as the upside-down entities they are, the interesting things are happening at the top (and the top of a volcano is at the bottom of the crust or even deeper).
Nobody has missed that Bárðarbunga is intensely seismically active and that it has been like that since prior to the onset of eruption. Problem is just that people are not grasping that the causation of the earthquakes has changed dramatically as time has passed.
During the time prior to the eruption and during the first couple of weeks the earthquakes were caused by magma intruding into bedrock and the magma reservoirs.
After that the main number of earthquakes was caused by magma very rapidly leaving the magma reservoir. In fact, magma moved out so rapidly that it left the poor main magma reservoir under-pressured, a state that remained until late summer 2016. The effect of this was that the entire caldera floor moved downwards into the magma reservoir.
Somewhere in October the pressure had increased enough from magma moving up from depth and the dropping caldera plug that the dropping stopped. The pressure was still far from the level prior to the eruption, but after that the earthquakes are caused by pressure increases from intruding magma.
This was further evidenced by the non-volumetric change non-double-couple M4.9 earthquake that occurred at 1.47pm on the 30th of January. These earthquakes are rare birds indeed and are almost all exclusive to Bárðarbunga.
They occur as slightly cooler magma in the upper magma chamber rapidly changes place with warmer magma at the lower magma reservoir. Therefore there is no change in volume in the volcano even though magma moves rapidly up (and down).
These large earthquakes happen about once a decade at Bárðarbunga and they do increase the amount of energy in the volcano and they are as such heralds of activity to come. But it is also good to remember that the last large one (+M5) was in 1996 and the subsequent eruption occurred in 2014, so they are not a sign of an impending eruption as such at Bárðarbunga.
The Icelandic Met Office held a meeting to discuss that swarm and concluded pretty much the same as I have written up above. “A meeting was held Friday to discuss seismic activity in Bárðarbunga. There, scientists concluded that many years will go by before magma pressure reaches a level as high as it was prior to the eruption of 2014, but they do not rule out volcanic activity in coming years.”
In other words, if anything happens in the next few years it will most likely be a small eruption, but even that is not likely in the next couple of years regardless of the intense seismic activity.
The Grímsvötn eruption of 2011 was the largest eruption in Iceland since the 1783 eruption of Lakí. The amount of lava that formed ash and tephra was in the 0.9km3 (DRE) range and it also emplaced close to 1km3 of lava on the bottom of the caldera.
As such it should be counted as a VEI-5 eruption, but the happy Icelanders are adamant that if it is not a cubic kilometer Dense Rock Equivalent of ash it is not a VEI-5, the rest of the planet uses 1km3 of ash and tephra that is not recalculated into Dense Rock Equivalent as the point of decision. Be that as it may, it was the largest eruption on the planet since the October 1991 eruption of Mount Hudson in Chile.
The effect of this large eruption from Grímsvötn is that it lost a lot of magma in the responsible magma reservoir. In a way, this is the same thing that happened at Bárðarbunga in 2014, it will take a longer time for Grímsvötn to recuperate since the magma influx into Grímsvötn is unusually steady for a volcanic system.
Problem is just that the volcano has 3 separate magma reservoirs, so just because one is low pressured does not automatically mean that the other two are low pressured.
The eastern magma reservoir is almost entirely inactive and is believed to be containing stale cooling magma and is as such unlikely to erupt unless it receives a large dollop of fresh magma. The Northwest magma reservoir had a large eruption during the 1996 Gjálp event and is still recuperating after that.
The last eruption was at a central-south magma reservoir and that one will need several years to build up in pressure and magma.
The problem here is that there is a fourth magma reservoir. I know that I just wrote that there are 3 reservoirs in Grímsvötn, and the answer to that conundrum is that the fourth chamber is located under what is believed to be a separate central volcano named Háabunga SSW of Grímsvötn proper.
The main bulk of the seismic activity has been in, around and at fissures emanating radially from this volcano after the 2011 eruption of Grímsvötn.
Normally it is very easy to predict when Grímsvötn will erupt, you just measure the increase in pressure as evidenced by cumulative seismic moment plots. As magma moves in the pressure increases and earthquakes will occur as rocks fracture around the magma chamber.
Problem is just that this is a very useful tool for the two known active reservoirs of Grímsvötn that we have good records of. We are not entirely sure if this is also true for a behaviorally unknown volcano such as under Háabunga.
For all we know it could have had several intrusions over the last 100 years or so and be primed to erupt, it could also require several more intrusions. We do though know one thing, and that is that it is an open conduit system as evidenced by the silent intrusion that occurred a couple of months ago. Normally this would have caused a large earthquake swarm around the magma reservoir, but since this did not happen I suspect that the pressure is still fairly low in this volcanic system and that it will take time before it will be able to erupt.
If it will be Háabunga that erupt, it will take anything between 6 months up to 100 years before it erupts. And when it happens we will not know the characteristics of the eruption. I am though quite convinced that we will see a lot of seismic activity in the weeks prior to an eruption.
The other option is that we will see a regular Grímsvötn eruption, and if that is the case we must wait anything from 6 months to 3 years depending on the level of seismic activity that will be indicating the regular pressure increase.
We know from GPS records that Hekla had recuperated back to the same level as prior to the 2000 eruption back in 2011. This lead to a false runup to eruption in 2013 that had the Icelandic Met Office issue an alert. I was also convinced that it would erupt then, but Hekla fooled us all back then.
I have lately been toying with the idea that you can predict a Hekla eruption with the same type of predictive tool as I use for Grímsvötn, or in other words Cumulative Seismic Moment plotting. The only thing is that there is no public available record spanning decades as it is for Grímsvötn. There may be such records at the Icelandic Met Office, but even those records would be intensely skewed by the increase of sensitivity in the system due to technical development and increase in the number of seismometers around Hekla.
But, the partial record that we all can see is giving off a couple of clues. If the idea to use CSM as a predictive tool is true there should over time be an increase in the amount of released strain in the form of earthquakes that is logarithmic. And if we look at the plot there seems to be evidence of that, but it is not statistically proven in any way. To go from my theory to get a useful statistical predictive tool we would need at least two complete cycles of eruptions (preferably more). At Grimsvötn we have 4 recorded cycles (1996, 1998, 2004 and 2011) that shows the same pattern.
Giving a time frame for Hekla is therefore very hard to give. We do know that the pressure is high, we do know it almost caused an eruption in 2013 and after that the rate of earthquakes has increased at what looks like a logarithmic scale.
As such we do know that it is very close to erupting, but due to the lack of long-term records we can’t give a definite answer of when it will occur. We know that the runup at the volcano is very short, so Hekla could erupt at any time from 30 minutes to 10 years into the future.
Currently I hold Hekla as the most likely Icelandic volcano to erupt in 2017, but that the caveat from up above still stands.
As we get to Katla things rapidly become very muddy since it is the only volcano out of the four that we have no instrumental record for prior to, during runup and during an eruption. Even the written accounts from previous eruptions are unusually unclear for being from Iceland.
That being said, we do have a very good instrumental record from 1990 and onwards, and it just become more excellent as the years pass by. One thing we could do is to compare Katla to other large caldera volcanoes that has erupted in instrumented times, namely Bárdarbunga and Grímsvötn.
The problem there is that the pattern emerging does not comply to what these two volcanoes are doing during their respective volcanic cycles. So, we are not getting any help at all there.
In the end, we must go back to the fundamental physics of a volcano near a mantleplume and take it from there and compare that to the instrumented records that we do have and make educated guesses.
Magma is formed at the bottom of the crust and moves up into a volcano like Katla and we know this has happened several times since 1990, last time it happened was in 2011. Now some of you will be pointing out that we are now seeing larger earthquakes than has ever been recorded at Katla and that must mean that magma is moving up. Problem is just that when magma is moving upwards in Katla the earthquakes start at depth and then move upwards and almost all of the earthquakes we have seen lately are very shallow.
I will now try to explain what is most likely to be happening in Katla that is causing these larger than normal earthquakes and what effect they may have upon the risk for an eruption in the near human future.
The previous intrusions have emplaced magma in a shallow magma reservoir with an estimated top at 3 kilometres’ depth. Since the hot magma is buoyant it is exerting pressure on the lid as it tries to move up and that is causing fractures to happen.
These fractures in turn can conduct fluids, be they tendrils of magma moving up, or meltwater from the glacier on top moving down. So far, the tendrils of magma have been too small for an eruption to occur and they have been rapidly cooled down corking up the fractures. They have though created an abundance of hot areas and they are heating up the water so much that they flash into superheated dry steam, and that flash turning also creates fracturing that magma or water can move into.
In a way, this process of magma/water interaction has turned into a large engine that is slowly mulching up the roof of the magma chamber. At some point the lid will be too cracked up to be able to contain the pressure and when that happen things will likely happen rather quickly. In this case, it could take anything between a few hours to a couple of weeks from the point of when we get a continuous earthquake swarm to onset of eruption.
So, if you see a powerful earthquake swarm start that goes on for a few hours and then just goes on and on, then it is time to expect an eruption.
Right now, the volcano is teetering on the brink of what pressure the roof above the magma chamber can hold, and it will most likely break in the next couple of years unless things calm down considerably.
One thing is though clear, the volcano is beyond being able to withstand another magma intrusion from depth, both volume wise and energy wise. And the fresh magma would be hotter than the magma in the magma chamber, so it would not only expand the chamber, it would also cause the pre-existing magma to heat up and inflate. If that happens we would have about 2 days to 2 weeks before an eruption occurs.
To return to what Páll Einarsson said in the article. It is the job of Icelandic volcanoes to get ready for an eruption and then they do erupt when they are ready. So, in a sense of it, nearing an eruption is something that they always do. The trick is to correctly estimate and predict when they will do so.
At the current level of understanding volcanoes, we can make long-term forecasts for volcanoes based on percentages of eruption risk for up to a decade in advance, but we can only accurately predict an upcoming eruption between 1 year in advance to 1 hour in advance depending on the volcano at hand.
If we make a forecast we see that all 4 volcanoes are likely to erupt within the next decade, but that does not come as a surprise. If we instead try to predict these volcanoes the picture become slightly different since the short timespan for which we can accurately predict volcanoes.
Currently we see that a prediction for Bárdarbunga and Grímsvötn are negative. We do know that they will not erupt in the timeframe we can predict them. We can also see that they are likely to not erupt in 2017 unless something rapidly changes, and if that happens the prediction would by necessity change.
Hekla ends up hanging in the country between a forecast and a prediction. We do see forecast signs that it is nearing an eruption, but the extremely short time it is possible to predict an eruption at that particular volcano means that we can only accurately predict it minutes to hours prior to onset of eruption. Remember that all Hekla will give away is a small smattering of earthquakes and then the gates of hell open up (ice cream sold at convenient locations).
Katla is further along towards the prediction stage when we can say when it will erupt and where. We are fairly certain that it will be a central caldera eruption, we can be fairly certain that it will be a VEI-4 or VEI-5 eruption, and we can be fairly certain that magma buoyancy and lid fracturing will be enough to break through within the next two years and if that does not happen one of the frequently occurring intrusions will be around the corner and that will assuredly take care of business.
Unless something changes drastically Katla will erupt within the next couple of years at the going rate of seismic activity.