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A landslide struck Askja's crater lake on July 24, 2014, weeks before the volcanic earthquake swarm began in southeastern Iceland.  In 2010 a geologist reported that Askja's magma chamber was inflating and predicted increasing volcanic activity. Magma from the Bárðarbunga volcano, intruding into a 40 km long set of fissures at depth, is now moving towards the Askja volcano which erupted violently 7,700 years ago creating this caldera.

Code red has been downgraded to Code orange by Iceland's Met Office because eruption is not imminent, but experienced vulcanologists have been stunned by the growing 35 - 40km long dyke which now connects the fissure systems of Iceland's three largest volcanoes. As a general rule, eruptions stay on the fissure systems of one volcano because magma will follow a fissure system's existing planes of weakness. The forces controlling the movement of magma now are acting on a larger scale than the scale of one volcano. While Iceland's Met office is speaking calmly of a possible small eruption other vulcanologists are discussing the possibility of a large rifting eruption that could have major impacts on Iceland and possibly Europe. (Please read Rei's series of reports to understand the possible impacts.)

The dark blue dots represent earthquakes that began on August 16 at Bárðarbunga. Red dots are today's earthquakes. Earthquakes are color coded by day.

Apparently, a block on the northeast side of Bárðarbunga's inner and outer calderas dropped blocking access to Bárðarbunga's fissure system and magma moved southwest along the fault where the block dropped down. Bárðarbunga's magma then found a zone of weakness on Grimsvotn's fissure zone and headed northeast. What's really surprising and concerning is the north turn of the earthquakes out of Grimsvotn's fissure zone towards Askja. It isn't clear how, but apparently the inflation of Askja reported in 2010, or recent rifting forces altered the stress field northeast of Bárðarbunga. Bárðarbunga's magma was captured by Askja's fissure system and is now heading towards the south side of Askja's caldera.

If the fissure stops moving north towards Askja, the Met Office's scenarios, stated in today's update, are relatively benign.

There are no indications that the intensity of the activity is declining. Currently, three scenarios are considered most likely: 1) The migration of magma could stop, attended by a gradual reduction in seismic activity. 2) The dike could reach the surface of the crust, starting an eruption. In this scenario, it is most likely that the eruption would be near the northern tip of the dike. This would most likely produce an effusive lava eruption with limited explosive, ash-producing activity. 3) An alternate scenario would be the dike reaching the surface where a significant part, or all, of the fissure is beneath the glacier. This would most likely produce a flood in Jökulsá á Fjöllum and perhaps explosive, ash-producing activity. Other scenarios cannot be excluded. For example, an eruption inside the Bárdarbunga caldera is possible but presently considered to be less likely.
But what will happen if the magma continues to move north without erupting for a few more days?

Update 11AM EST 26Aug14 Earthquakes Continue Moving North towards Askja

Stronger and deeper earthquakes have been observed in the last 12 hours near the tip of the growing fissure. This may be evidence that the rock is colder and stronger in this region which has thicker crust than directly under the hotspot where the fissure started.  Crustal rocks above a certain temperature are ductile and don't rupture in earthquakes. The lack of earthquakes below 15 km provides a lack of information on what's happening below that depth. It is not evidence that nothing is happening. The M 4.6 earthquake near the rupture tip just before noon today Icelandic time was the largest earthquake observed away from the caldera. The M5.7 earthquake after midnight on the north side of the caldera was the strongest earthquake yet in this earthquake swarm. Iceland's Met office reported that 50 million cubic meters of magmawas injected into the dyke system yesterday.

As the rupture pushes north the odds of a violent eruption increase.

Volcanologist Haraldur Sigurðsson claims that it is possible that the underground magma from Bárðarbunga may seep into the volcanic system of Askja volcano and ignite a powerful eruption in that region. Still, he thinks it is more likely that the current activity will not lead to any activity above ground.

Haraldur talked to reporters at Stöð 2 and RÚV yesterday and reminded them of the Askja eruption in 1875, which led to years of hardship in Iceland and contributed to the massive exodus of Icelanders to America.

Beautiful 360 degree panoramic view of Askja at this link.

----- End Update ------

The scenarios become more serious. And we're already talking about a large volume of magma based on GPS measurements. Kudos to Carl at VolcanoCafe.

So, let us just say that Bárðarbunga is the largest volcano of its type on the planet, and that it has had the largest lava flood eruptions in the last 10 000 years, and that it is prone to have what is called rifting fissure eruptions.

A rifting fissure eruption is when a large part of the fissure swarm “rifts”. Rifting is when a large part of a fissure on Iceland opens up all the way down to the mantle and as that happens a large scale decompression melt starts in the mantle and obscene amounts of magma is formed and pushed upwards filling the void that is created as the tectonic plates move apart. ......

Dyngjuháls (DYNC) has changed its orbit slightly and the rapid north motion has shifted to a slow south motion as the intrusion has passed the GPS-station. The westwards motion goes on unabated and the station has now moved 185mm in that direction.

If we look at the Kverkfjöll station named Gengissig (GSIG) we see 90mm of southwards motion combined with 180mm of eastwards motion.

If we now combine the west motion of DYNC with the east motion of GSIG we get a total rifting of 365mm in 8 days. That is an average of 45mm per day, or the equivalent motion of 14 years of normal Icelandic rifting done in only 8 days.

These two stations are though a bit distant from the rifting fissure, so the rifting is obviously larger than that. Most likely the rifting right on top of the dyke is in the order of a meter or more. This means that more than 0.8 cubic kilometers of magma has intruded.

Now, even that number is on the low side since the “lips” of the rifting fissure are still closed. As the lips open the total rifting will most likely be closer to ten or twenty meters if it occurred now. And the longer the intrusion continues before onset of eruption the larger the fissure opening will be.

So, a very large fissure eruption is possible. As told by Rei the gasses from this type of eruption could be devastating to Iceland and Europe.
The winter of 1783-1784. The Revolutionary War had just ended, and Benjamin Franklin was puzzling over the nation's bizarre weather. Congress had been delayed getting to Annapolis to vote for the Treaty of Paris because the Chesapeake Bay just wouldn't melt. The Mississippi River froze down to New Orleans, and ice was reported floating in the Gulf of Mexico. Reports from Europe were of a bizarrely hot summer with thick fog that was choking people to death in Scotland, massive hailstones, lightning, and crop failures. The sun was blood-red at noon. Mass starvation that would ultimately kill 1/6ths of Egypt's population took hold due to a historic drought of the Nile. As many as six million people would die from the bizarre weather.

Franklin was one of the few scientists of the era to (almost) correctly speculate as to its cause:

    "The cause of this universal fog is not yet ascertained [...] or whether it was the vast quantity of smoke, long continuing, to issue during the summer from Hekla in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds, over the northern part of the world, is yet uncertain."

He, however, had mixed up his Icelandic volcanoes, for it was not Hekla that erupted that year, causing the planet-altering weather, but Laki (Eldgjá). A rift 23 kilometers long opened up in places up to 100 meters wide with lava fountains at times reaching over a kilometers into the air - and it continued erupting for 8 months.

But that's not what concerns me. I'm concerned about Askja. There's something about Askja that makes it more violent than Bárðarbunga. Iceland is the only place on earth where a mid-ocean ridge, a hotspot and granitic rock come together and the place where they come together is Askja. Unlike other mid-ocean islands Iceland has a thick crust in the central region because the hot spot is captured on the ridge and they rate of lava production has been high relative to the spreading rate.
Thickness of Iceland's crust.
The crust of central Iceland is twice as thick as normal oceanic crust.
This thickened crust has pushed down basalt to depth and the basalt has partially melted to produce granitic intrusions at depth.And that makes for trouble at Askja. The world's most violent volcanoes are located at continental hotspots where basaltic magma interacts with granitic rocks. Yellowstone, Wyoming; Valles Caldera, New Mexico; and Long Valley California are 3  explosive volcanic systems that produced catastrophic eruptions when injections of mantle basalt melted granitic rock.

There are 2 things about injecting basalt from the mantle into granitic rock that make for large dangerous eruptions. Granite is higher in silica than basalt so it is more viscous. Instead of flowing smoothly it is sticky so it tends to erupt violently. The second aspect is more subtle. Granite melts at a lower temperature than basalt so the injection of basalt into granitic rock can produce a larger amount of melt than was initially present. Both of these factors contribute to producing large highly explosive eruptions.

The 1875 rhyolitic eruption of Askja volcano in Iceland was a complex but well-documented silicic explosive eruption. Eyewitness chronologies, coupled with examination of very proximal exposures and historical records of distal deposit thickness, provide an unusual opportunity for study of Plinian and phreatoplinian eruption and plume dynamics. The ∼ 17 hour-long main eruption was characterized by abrupt and reversible shifts in eruption style, e.g., from ‘wet’ to ‘dry’ eruption conditions, and transitions from fall to flow activity.

The main eruption began with a ‘dry’ subplinian phase (B), followed by a shift to a very powerful phreatoplinian ‘wet’ eruptive phase (C1). A shift from sustained ‘wet' activity to the formation of ‘wet’ pyroclastic density currents followed with the C2 pyroclastic density currents, which became dryer with time. Severe ground shaking accompanied a migration in vent position and the onset of the intense ‘dry’ Plinian phase

Askja's last big explosive eruption was in 1875 but geologic evidence shows that prehistoric eruptions were much larger and more destructive. The present caldera that was formed by an explosion 7,700 years ago in is the caldera of a much larger, older eruption.

And, the latest report at 19:09 Icelandic time is that magma continues to move towards Askja.

Until 19:00 today, around 1.200 earthquakes have been automatically detected under northwestern Vatnajökull. The vast majority have been around the northernmost tip of the dyke intrusion at Dyngjujökull. The tip of the earthquake cluster has migrated further to 6-7 km north of Dyngjujökull.  More than 20 events at the tip of the intrusion were between M3 and M4.  Event depths are still around 5-12 km, no sign of upwards migration or low frequent tremor. One earthquake  M5.1 occurred within the Bárdarbunga caldera at 16:19 today. Otherwise, little activity has been within the caldera today.

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