The Calm before the Storm

Water drainage basins at the glacier bed for the principal rivers draining Vatnajökull. Subglacial water-filled cupolas, located under depressions in the glacier surface, collect meltwater and periodically drain by means of jökulhlaups. In order to determine water divide locations on a regional scale, a model was employed which assumed that water pressure at the glacier bed is approximately equal to the ice overburden pressure. – Vatnasvæði helstu jökulfljóta sem falla frá Vatnajökli. (From Reviewed Research Article ” Icelandic Glaciers ” By Helgi Björnsson and Finnur Pálsson)

First, a few reminders:

* The vedur / en.vedur servers are VITAL to the Icelandic authorities responsible for Public Safety. Do not UNDER ANY CIRCUMSTANCE post a link / picture here or on ANY other website as this can cause and has caused their main server to crash!!! .
* Official news (stone tablets) will be issued through the appropriate Icelandic authorities as and when. Do not treat or quote what is published on VolcanoCafé as official news! This is a blog and much of what is posted here is speculative.
* While we all want to know what’s going on, please restrain your curiosity! Especially if there is an eruption as literally hundreds of thousands of people will want to know. The servers will crash, so don’t overload them with continuous refreshs (F5)!
* While we try and respond to questions as much as we can, please understand that none of the “staff” at VolcanoCafé are employed! We are all volunteers. Almost all of us have regular jobs to take care of first and foremost. In a crisis such as this, we ask you please to respect that our foremost concern is to keep the blog open and running, updating it as expediently possible!
* Please spare a thought for those who visit this blog looking for information and who may be very worried about the ongoing events, especially if they are likely to be directly affected if a large-scale eruption occurs. Many of our newcomers are knowledgeable, but others are not, and are perhaps unable to filter what is a genuine scientific appraisal from what is speculative armchair theory. While the nature of what might or might not happen is naturally providing a source of good-spirited, healthy and fascinating debate, during which speculations and assumptions abound, remember we are an amateur science blog and not a place for alarmist doomsday talk that has no basis in fact. Please pause a second to think about this before posting your views.

The most important news from the morning is what the premier expert on subglacial eruptions, Professor Magnús Tumi Guðmundsson, said in an interview for RUV (in Icelandic):

http://www.ruv.is/frett/veruleg-ovissa-um-hvad-er-ad-gerast

Sigkatlar = Ice Cauldrons

http://www.ruv.is/files/myndir/sigkatlar_klukkan_23_52_agust_27_0.jpg

Map (RUV) of the NW part of Vatnajökull showing the location of the Ice Cauldrons mentioned by Professor Guðmundsson

The last time this happened was at Katla in 2011 when there was a small, subglacial eruption that resulted in several such cauldrons and a small jökulhlaup that nevertheless was powerful enough to remove a bridge. This does not have to be an actual magmatic eruption. The enormous amount of heat introduced has caused tremendous hydrothermal activity which is evident from the blue, 2 – 4Hz tremor lines.

http://img.visir.is/apps/pbcsi.dll/storyimage/XZ/20140824/FRETTIR01/140829515/AR/0/AR-140829515.jpg?NoBorder

These “sigkatlar”, Ice Cauldrons, are from the days just before the 1996 Gjálp eruption (Visir, Is)

Earlier today, scientists from the Icelandic Meteorological Office and University of Iceland took a number of flights over the region. Icelandic journalist and pilot Omar Ragnarsson who reported on this issue was involved in another flyover. The biggest development was the discovery of a number of depressions, “sigkatlar” or ice cauldrons, in the glacier that caps the volcano’s caldera. These cauldrons number over a dozen and are relatively shallow, only 10-15 metres, and form a string that spans some 4-6 km along the surface of the ice.

https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/10615991_930527610307051_6654128250262433774_n.jpg?oh=3204024102c96eb091c8dbbf73ce5bb0&oe=54715721&__gda__=1416513789_1a21004b0518f5f6b023caf6457fa5f2

Video: http://www.ruv.is/frett/sprungur-i-holuhrauni-a-myndbandi
When looking at the video: The flight path entered from Skaftáreldar, then overflew the Bardarbunga central volcano after which the aircraft circled the Dyngjujökull where there are several cracks in the glacier as well as a (monogenetic) cone from a previous eruption.

For the sake of clarity, it is perhaps best to divide the summary between the two areas of activity, Bardarbunga and the front of the intrusion moving north.

Bardarbunga

All events shown are over Mag 3 – the date and time of the event is shown in the title bar

Over the past days, mention has been made of a possible subsidence of the Bardarbunga caldera due to magma flowing out from under the Central Volcano and into the main dike. What is certain is that the massive amounts of heat introduced by this magmatic intrusion has activated the hydrothermal system – water in cracks in the ground going down several kilometres – underneath the volcano. This is evident from the heightened activity in the blue 2-4Hz line of the tremor plots. The appearance of the Ice Cauldrons mentioned by Professor Magnús Tumi Guðmundsson point to activity between the glacier and bedrock which can be explained by either a) the increase in hydrothermal activity, and/or b) an ongoing magmatic eruption, possibly a couple of kilometres in length as indicated by the location of the “sigkatlar”, ice cauldrons.

The Intrusion Front

All events shown are over Mag 3 – the date and time of the event is shown in the title bar

Continued earthquake activity indicates that the intrusion is still progressing northwards towards Askja but at a slower rate. In the interview for RUV, Professor Magnús Tumi Guðmundsson said that the dike may run as far down as a depth of 18 km which could be interpreted that it runs from a depth of 5 to 18 km at its maximum extent. Our own Carl Rehnberg, PhD, says that his personal tracking of the earthquakes yields this figure for most of its length but that it in two locations expands to 2.5 by 20 km.

Possible Jökulhlaup

According to Professor Guðmundsson “Around 30-40 million cubic meters [1,1-1,4 billion cubic feet] of water have flowed from under there but we don’t know whether this has been happening in the past days or just today [yesterday]. However, by what we can see on earthquake monitors there are no indications of a great volcanic eruption taking place.”

This while substantial is enough water to form only a smaller, yet potentially lethal jökulhlaup. The amount corresponds to the content of 12,000 to 16,000 Olympic size swimming pools (Olympic swimming pool = 2500 cubic metres).

DracoPyrite

with assistance of dfm and the dragons

This is the update with no zoom.