10pmEDT Update 3
A M5.3 earthquake, the largest to date in this swarm of earthquakes, was centered at 5 km depth on Bárðarbunga volcano's caldera boundary ring fault.
Very low clouds and steam, possibly from Bárðarbunga, are now apparent near the edge of Iceland's southeast icecap on the livecam.
Other reports of the eruption based on images from a nearby webcam were also in error—it was simply a sandstorm passing through, which is a common occurrence in the area.Live blogging situations like this is a challenge. Because the earthquake swarm generated by magma pushing north in a fracture zone will likely reach the edge of the ice cap by tomorrow, the situation will be much clearer very soon.
The situation is unclear. Here's the latest Icelandic Met Office update which maintains the red alert, but steps back from declaring the eruption has started.
At 11:20 UTC today, seismic tremor measurements gave a strong indication that an eruption beneath Dyngjujökull was occurring. Tremor levels decreased during the afternoon, although intense earthquake activity continues. An over-flight was made to Bárðarbunga and the north-western region of the Vatnajökull ice-cap in clear conditions. Both visual observations and radar measurements confirmed no significant changes on the surface of Vatnajökull. Likewise, there were no signs of floodwater draining from the ice margin. In light of the intense, ongoing earthquake activity and crustal deformation at Bárðarbunga, the Icelandic Meteorological Office has decided that the aviation colour-code should remain ‘red’. The situation will be reassessed tomorrow morning.- end update 2
Written by a specialist at 23 Aug 21:04 GMT
The peak in high frequency vibrations indicates the beginning of the eruption. The change from low to high frequency vibrations shows when the underground dyke injection of magma began.
It is believed that a small subglacial lava-eruption has begun under the Dyngjujökull glacier. The aviation color code for the Bárðarbunga volcano has been changed from orange to red. Just now (14:04), an earthquake, estimated at magnitude of 4.5 was detected.
I will be updating this diary continuously. I intend to post complementary material to the excellent posts by Rei (66,000 Facebook likes and counting), from Iceland. I will add background information on the geology of Iceland after I get the immediate information posted.
Update 3:30pm EDT
EarthquakesAn Icelandic expert stated that a recent helicopter overflight did not find a tell tale depression in the ice cap which would be evidence of an eruption. We will know tomorrow if an eruption has occurred because melt water would reach the edge of the glacier in 20 hours. --------
The frequency of earthquakes is so high, that the events are overlapping in time, and it is difficult to discern individual events. We are currently interpreting the depth of the majority of earthquakes (5-10 km) as the depth of the base of the dyke. The dyke has propagated about 5 km to the north since yesterday.
Most recent GPS data shows that magma flow is continuing. Since the start of unrest on August 16th, the total displacement across the dyke intrusion has been over 20 cm. A model to fit the GPS data suggests that the volume of magma contained within the dyke is approximately 250 million cubic meters. The Dyngjuháls and Kverkfjöll GPS stations show continuing deformation
The eruption is towards the edge of the ice cap where the ice is not thick enough to contain the eruption for long. In my estimation as a geologist who does not claim to be a vulcanologist (but knows a lot of geochemistry and geophysics) there's a high probability that the eruption will break through and turn violent. The pressure of thousands of meters of water or ice can contain an eruption. On the other hand, when the ice cover is not thick the ice cover will melt and uncap the lid over the eruption, leading to both massive flooding and a potentially violent eruption.
It is estimated that between 150-400 metres of ice are located above the eruption area.Because the dyke injection continued in a northward direction towards the edge of the icecap it apparently broke through quickly. Now the big questions are how big and how violent will this be. This volcanic system has the potential for mind-boggling eruptions, some of the largest on earth, but small to mid sized eruptions are far more common and likely.
Automatically generated earthquake maps can be hard to interpret because they are prone to errors. Careful analysis and manual correction of seismic data produces better maps that give a much clearer picture of what's happening underground. Earthquake depths from automatically generated data sets are simply not reliable enough to determine the depth of moving magma. Earthquakes larger than M2 are detected by more seismometers, and can thus be located more reliably than micro-earthquakes. Manual corrections of the larger earthquakes by Iceland Met office seismologists has produced a map that clearly shows the underground pathways from the central caldera to the surface eruption.
The large Icelandic volcanoes are situated on something called fissure swarms; those are permanent thin areas of the crust that are permanently weakened as the continental plates pull apart. They are in a sense of it the actual rifts where the Mid Atlantic Rift (MAR) pulls apart.I, however, am not surprised by the interaction between the volcanoes. I have studied fault systems in California and Nevada that behaved in unexpected ways when multiple faults were involved in complex earthquakes. In Iceland the heat of the combined mid-Atlantic rift and the captured mantle plume make the rocks of southeastern Iceland very hot and weak. Weak rock and weak forces separate one volcano from another. That is one factor that makes the behavior of Iceland's volcanoes very unpredictable.
Under Vatnajökull there are at least 3 fissure swarms, Bárðarbunga fissure swarm (Veidivötn to the South and Dyngjuháls to the North) Grimsvötn fissure swarm (Lakí to the South and Grimsvötn to the North) and Lángisjör. The last one we can leave for now.
On the fissure swarms you have central volcanoes. 3 are known for the Bárðarbunga fissure swarm, namely from North to South Kistufell, Bárðarbunga and Hamarinn. For Grimsvötn you have Grimsvötn, Háabunga, Thordarhyrna, Geirvörtur, Háagöngur and Éldgigur.
The central volcanoes interact with their fissure swarms in many intriguing ways. But it has been the general opinion that each fissure swarm is a system on their own. There are a couple of hypothetical places where it is suspected that some sort of mechanical interaction could exist, but there has never been any clear cut proof of it. And there has never been any proof or even a causal chain proving movement of magma in between them.
Until now. First I need to explain one last detail before we get to our lovemaking fissure swarms.
Radial fissures are fissures that extend outwards from a central point, in this case a central volcano. Think of it like the spokes on a bike wheel. Several are known for Bárðarbunga, the most well known is the Gjálp fissure that erupted in 1996 that extends from Bárðarbunga towards Grimsvötn. In the beginning there were two earthquake swarms. One happened at the Kistufell central volcano. We can leave that one be today. At the same time a small swarm happened inside the central volcano of Bárðarbunga that quickly moved into and along a radial fissure.
As the magma followed this radial fissure it went so far out that it encountered a new feature, the Grimsvötn fissure swarm. At that point the magma was injected into a more fertile ground and for pressure dynamic reasons it could not go towards Grimsvötn, instead it started to move further down stream of this new fissure swarm.
Now I just hope that Bárður and Grims baby will not take 9 months of birthpangs until being born.
I can’t stress strongly enough how surprised I am about this. It is the single biggest surprise in my volcanic days. It is surprises like this that makes life truly worth living.