Richie, one of our readers emailed in a good question that is a good starting point for a brief update on Bárðarbunga.
“Could you do an article comparing this intrusion to others? Looking at the post it appears that it is almost 40 Km long but how wide is it and in terms of volume. I am not sure if any diagrams are available to give an indication of the size underground. ”
It is hard to compare this intrusion to any other that we have instrumental data on. The main reason is that we have not seen one like this from a mantleplume volcano, nor have we seen something like this from a rift volcano.
It has a little bit of semblance from the Krafla Fires rifting episode. But I think that comparison is just too simple. First of all that was a much thinner intrusion that never reached this deep, so it was never even close to get down to the mantle. And the most obvious thing is that it kept to its own fissure swarm.
This intrusion has now been inside 3 different fissure swarms, and has the potential for more magma output when it breaks to the surface. In a way it is much closer to how the Skaftár Fires (Lakí) looked, but that eruption also seems to have stayed within its own fissure swarm.
I would now say that it is a unique intrusion and that makes it all the harder to understand and potentially more dangerous.
I am not aware of any exact diagrams or plots of the intrusion, but Tom made a couple that is interesting where he compares two possible solutions for the shape. One is a bottom closed intrusion with no mantle contact, and the second is a full Skaftár Fires version with a wedge shaped obloid intrusion open down to the mantle.
I currently think we have the first option, but that it is really close to the mantle and that it sooner or later will turn into option two. If I am right this will most likely lead to an increased risk for a flood basalt event.
The rift is now 45 km long and roughly 17.5 km high. Calculating the width is though a bit more interesting. If we take the east and west dilation between the Dyngjuháls (DYNC) and Kverkfjöll (Gengissig, GSIG) is by now 44.5cm. To get the correct values we have to take to recognize that the GPS-station are a bit far from the rift so the value is larger. Now, if we compare with the apparent dilation on further out stations we can roughly calculate that the true value is around 135cm. That would make the current volume of intruded magma into 1.05km3.
Update on Bárðarbunga
At the going rate the intrusion will slam into the eastern side of Askja’s magmatic system in 2 to 3 days. The effects of that could become slightly troublesome.
The large earthquakes are continuing at the caldera of Bárðarbunga and it seems like at least a partial ring faulting might take place there as magma rushes out from the magma reservoir. On the other hand the lowering of the caldera floor seems to be fairly small so the influx of magma is barely smaller than the amount going out into the opening rift.
Earlier tonight I noticed something interesting in the next volcano over. And that is that according to the Grimsvötn GPS it seems like the volcano is pulsing. That is a bit odd for a volcano that is not erupting and looks like it is not doing an intrusion of itself. And it becomes even more quirky since it seems to happen at the same time as the Bárðarbunga intrusion hits roadblocks.
One intriguing possibility is that the Bárðarbunga intrusion hit an old intrusion in Grimsvötns containing molten material and that it due to higher pressure in the Grimsvötn system took that infamous left-hand turn down Grimsvötns fissure swarm. It would certainly explain the marked pulsing on the GPS plot. Having Iceland’s two largest volcanoes force feed a rifting dyke could become slightly interesting in the future if it is correct.
Using Down Under ( Andrew)´s comments:August 27, 2014 at 05:04
Everybody, please welcome the dike into the Askja domain.
He also did some trajectories starting August 28th
and August 29th:Down Under (Andrew) August 27, 2014 at 05:08