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So what happened yesterday? Because, frankly, the ongoings near Bárðarbunga's caldera were both unpredicted and kind of weird.

There were the surface signs of a subglacial eruption (sigkatlar), appearing overnight... but no apparent eruption tremors.

They appeared southeast of the caldera... where nothing major has happened, seismically, in nearly two weeks.

A large amount of ice disappeared, presumably melting to water... but none of the river flows increased measurably.

And then the day after they flew TF-SIF, the coast guard research plane, over the site... they remained unchanged.

I guess that's just par or the course for this strange course of events. Let's break it down and its implications in this edition of Eldfjallavakt.

(Update: See the bottom of the diary. While I was busy writing a diary about how I thought the thing might soon erupt on the northern end of Dyngjujökull, the darn thing went and erupted just north of Dynjujökull!  ;) )

These may not look like much, but each of those depressions are 4.5 kilometers long, 1km wide, and 10-20 meters deep. And they appeared just in one day. What could do that?

Scientists seem now to agree that it was a small, brief subglacial eruption.

We know from yesterday that these represent 30 to 40 million cubic meters of meltwater. But how much magma does that represent?  Thankfully this is fairly easy to work out an approximate answer to. Ice takes 333.55 joules per gram to melt, plus 4.18 joules for every degree celsius the temperature changes. If the ice is at -10C then the total needed is 375.35 J/g. The specific heat of basaltic magma is 1.0 J/g and for solid basalt it's 1.4 J/g. 400 J/g are released by it crystallizing. A realistic magma temperature is 1350C with a crystallization temperature of 1000C. So the top 350C represents 350 J/g, then we release 400 J/g, then finally 1400 J/g cooling all the way down to just barely over the melting point of ice - a total of 2150 J/g. From this, we determine that the ratio of magma to meltwater is 5.7 to 1, and thus, 35 million cubic meters of meltwater represents 6 million cubic meters of magma influx.

Is that a lot?

No.

The estimates of magma influx into the system has ranged from 20-50 million cubic meters per day, and some have argued that the magma flows are actually threefold higher than that. The amount that flowed out is only a couple hours worth, and is insignificant in comparison to the size of the dike or Bárðarbunga's magma chamber.

In short, this did almost nothing to let off pressure and will do nothing to change the odds of further eruptions.

Those who followed Eyjafjallajökull will remember that her eruption began with small lava eruptions on Fimmvörðuháls from two new vents called Móði and Magni:

(Yes, that's a small eruption  ;)  )

This pattern is not at all uncommon in Iceland, wherein a small lava eruption or mixed eruption precedes larger eruptions of different varieties. Not every conduit which finds a way to the surface carries a large volume of explosive magma. Askja's infamous 1875 eruption itself was preceded by a small, harmless mixed eruption for several months before her primary explosive event.

Why are the sigkatlar unchanged?

Well, that's easy - the eruption stopped. Why? Who knows. We know next to nothing about that. Or when it started. The science team yesterday was complaining about the difficulty of getting clear data because the quake activity is so intense in the region, it masks signals.

What happened to the water?

That's not fully clear either. The main theory is that it flowed into Grímsvötn, a volcano coinciding with a series of subglacial lakes. The evidence is that the ice over Grímsvötn raised up about 5-10 meters. But Professor Magnús Tumi thinks that's not enough. He's at a loss however as to where else it could have gone, as there's no way it could have escaped their river outflow meters, and is thus "somewhere" in the Vatnajökull hydrological system.

Residents downstream from Vatnajökull have been having meetings to review their evacuation plans s a precaution.

So why was the eruption in that location anyway?

The reason for the location, and why exactly this occurred, is still a mystery. But as noted, this minor eruption is just a side topic. Because the real story today is the conduit to the north.

Yesterday, the news was that the conduit had only advanced 1.5 to 3 kilometers. Today, it doesn't seem to have advanced at all:


That's good, right?

Well... one can't really say that. Because quake activity there is still just as intense:

The conduit is widening there. But there's something else going on. Note that there's actually two lobes. We have the tip - no surprise there. But there's a lot more quakes further back, under Dyngjujökull. This might be just interpreted as a fluke, except that this has been consistent. This is the area that the dike raced through after the cork popped, and there's been strong, if not growing, activity there every day.

Okay, so that's just a curiosity, right?

Well, maybe not. From the Met Office update, something which none of the media seems to have commented on yet:

In front of Dynjujökull, in Holuhraun and north of there, there are rifts which stretch about 5 kilometers north of the edge. The rifts form an approximately 1km wide region with the same direction as the dike which has moved to the north in recent days. These rits reach approximately 1 kilometer into the glacier.

Two small circular depressions are in the glacier just above. There seems to have been a minor amount of melting underneath, probably because of the heating up of groundwater because of the dike. All of these signs can be explained by the magma intrusion, and suggest that the depth of the dike there is hardly more than two kilometers.

Got that? Right where we're seeing most of the dike's activity right now, where it's widening the most, quaking the most, the ice is melting overhead.

Are we going to get an eruption there, and if so, will it be something little or big?

I have no clue in both regards. But it's definitely a point to watch. It could be yet another opening play to a long event.

Is the dike going to stop expanding toward Askja?

I think it's too soon to say that. It would be quite fortunate, but given that the dike has intruded into Askja's rift system and is already inducing quakes in its caldera, and all of this seismic activity continues unabated, I think that would be quite premature.

Speaking of rifts... I've got some videos for you.  :)  They took some lovely shots of the rift field created by the dike north of Dyngjujökull today starting halfway through this highlights film:

The rifts there have expanded 40 centimeters during this event, with the past 5 days expanding at double the rate. This represents 20 years of spreading in under two weeks.

Here's another, longer video from the TF-SIF research team:

The neat patterning on Dyngjujökull (visible about 3/4ths of the way through the video) - the black banding - is from past ash falls.

I want to see pretty pictures!

Um... okay, here you go.






There - I feel better! Don't say anything depressing!

Okay, I won't bring up that they're saying that this may keep going for a long time and "we could be entering a highly volcanic time period wherein volcanic eruptions will multiply", noting that even before this the rate of eruptions had risen significantly.

Yeah, you better not say anything like that!

Okay, I won't bring it up.

Update, 1:00 29 august: There's a New Eruption, right around where I was talking about while writing this:

That's lava, folks!

On the webcams of Míla, which are pointed at Bárðarbunga, one can see a large red glow. The Met Office has confirmed that this is an eruption, and says that it is north of Dyngjujökull.

The eruption is a lava eruption, and north of Dyngjujökull in Holuhraun. (Ed: Interesting.. not the main quake area, but still a quake area).Scientists in this field have confirmed that an eruption is in progress. Quake activity suggests that the eruption is outside the glacier.

Camera 1
Camera 2

I feel bad, I'd have gotten the story sooner had I not been writing the above diary when it broke! Anyway, we've now seen the opening act. Let's see how the plot develops from here.

Update, 1:40 29 august: Link

Rögnvaldur Ólafsson in the coordination center of the public protection services conirms in a conversation with Vísir that an eruption has begun north of Dyngjujökull but south of Askja.

"This is likely in the place where the dike ends going north," says Rögnvaldur in a conversation with Vísir. He considers that what we're talking about is a 200-300 meter rift but they're trying to position the eruption better.

Employees are collecting in the coordination center which got news of the report around 12:30. He says that scientists are in the area conducting research and that they will keep up with this progressing issue. It's believed to be pahoehoe / low viscosity lava.

"They see in the direction of it but are taking care not to get to close in the beginning" says Rögnvaldur. "There could be explosions."

Rögnvaldur says that they'll wait to send TF-SIF, the Coast Guard plane, until it's bright tomorrow. He doesn't personally know whether quake activity has been much this evening but he had just arrived."

"I'd been sleeping“..
Update, 3:15 29 august: One last update before I go to sleep.

Airspace over a good chunk of northern Iceland has been closed to instrument-only flights, you have to have visibility. The airport servicing the Akureyri Airport falls within the zone.

Scientists on the scene (1-2 km away) report that the erupting fissure is about 300 meters long, according to the RÚV twitter feed. There are reportedly no spectacular columns of fire of note.

Góða nótt!

Update, 9:15 29 august: Quick morning update. The rift is now 1 kilometer long. The eruption is said to be very beautiful, with 10 craters set up like a painting, according to Ómar Ragnarsson.

And yes... I got a vid for you all  :)

More later when I have a chance to catch up!

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