Let's get some figures for perspective.
15 meters: Height of a five story building. Three times the height of an adult giraffe.
850 meters: A bit taller than the Burj Dubai. Over double the height of the Empire State Building. Nearly 3 times the height of the Eiffel Tower.
0,25 cubic kilometers: 100 times the volume of the Great Pyramid. 16 times the volume of the Three Gorges Dam. 2.5 times the volume of the Eyjafjallajökull eruption.
Now let's use those figures. 850 meters of ice lie atop the caldera of Bárðarbunga, Iceland's largest volcano. And yesterday's radar measurements show that underneath it, the caldera has subsided by 15 meters, dropping by a volume of 0.25 kilometers.
And a caldera eruption is now considered more likely than ever.
More Eldfjallavakt below the fold.
If you've had a sinking feeling about all this, you're right.
So says the radar data from yesterday's survey plane. The caldera plunging down into the earth below the ice, at a rate greater than has ever been measured before in Iceland by modern equipment (by comparison, Krafla's caldera dropped a mere 2 meters). You'll notice a series of smaller depressions to the southeast, tracking the initial direction of dike intrusion, and which were later overlain by small sigkatlar. The deepest point there is a drop of 35 meters. This was the site of a small eruption. The subsidence is believed to be due to a quarter cubic kilometer of magma moving away from underneath the caldera into the dike, although whether this relates to a shallow magma chamber or deep reservoirs is not known.
But we're not here because of small eruptions. We began covering this because of the potential of a big eruption, from Bárðarbunga herself. And there's a growing belief that this data suggests that it's increasingly likely to happen.
Is what's going on at Holuhraun a way to prevent the eruption? According to geophysicist Magnús Tumi Guðmundsson, no. While it is erupting from Holuhraun it decreases the likelihood of a simultaneous eruption from the main caldera. But what's going on in Holuhraun is just the first stages in what's expected to be a long process, and in the long run it is just a delay.
But nothing is guaranteed at this point in time.
If she does erupt, however, Bárðarbunga is deep underneath very thick ice, and can erupt very quickly. So remember all of those flood scenarios discussed in the earlier diaries, the reason they were closing all of the roads in the first place? That's what we're facing from Bárðarbunga, plus an explosive eruption with major ash potential.
But for now, it's just a waiting game.
On Holuhraun, action continues in both the old and new fissures, with increase in activity on the old fissures, but a decline in activity on the new ones. Lava from the fissures is likely to flow into the Jökulsár á Fjöllum tomorrow, which should be an impressive thing to see, but also poses the risk of explosions. Observations continue on two depressions in the ice on Dyngjujökull; there's clear evidence of small past eruptions but no large current ones. The risk for sudden flooding remains high.
For a brief period, the plume from the eruption had switched from blowing into the arctic and instead launched a cloud rich in SO2 toward Ireland. While I did not expect to see much in terms of surface effects, I was wrong:
All across Ireland, SO2 levels spiked. Cork in the south hit 120 µg/m³. Spikes on Dublin stations (in the east) were up to around around 175 µg/m³. Portlaoise broke 200. And in the west, Ennis went so far off the top of the chart that it's hard to measure, but probably at least 300 judging from the curve, possibly significantly more.
The World Health Organization says that SO2 levels should not exceed 20 µg/m³ for a 24-hour period and 500 µg/m³ for a 10-minute period, otherwise you're likely to increase the death rate among pollution-vulnerable populations. Given that Ennis was in excess of 200 µg/m³ for several hours, it could potentially have caused health complications for people with respiratory disorders and other vulnerable populations.
But then it left. Because, quite simply, this eruption is young. It's dumping SO2 into air almost devoid of it, allowing it to dilute as it travels. Likewise, it was carried by just a random brief wind. A couple hours of high pollution levels may lead to a few premature deaths if that, but it becomes a different story where long-term release of volcanic gases and unfavorable wind patterns can lead to much more serious, protracted events. This is something we hope to avoid.
On the other hand, for Iceland, dilution isn't an option; it's all about emission rates and weather. Eastern Iceland has been under a blue haze since the eruption began. Due to limitations with of the gas meters, they were unable to measure it today, but estimate its SO2 concentration at 100-200 µg/m³. Thankfully, it's been (typically) windy, which helps keep surface levels of SO2 down.
Of the SO2 that enters into the atmosphere, most will leave over days to weeks, but a fraction will persist for months or even years. And sometimes even as it stands it can takes a surprisingly long time to dilute. A fraction of the SO2 from the first days of the eruption is now entering Siberia, a third of the way around the world.
Regardless, without an acceleration in the eruption rate or a very long eruption, this will probably only cause low-level health effects to the general population and limited climate effects. So let's hope for that. :)
Picture time.
Infrared (false color) image of the eruption:
Infrared image of a "fire tornado" taken by the FutureVolc project:
Northern lights over the eruption:
Steam over the lava flow:
And two videos for the day. First, some good aerial shots:
And then, a solid candidate for "most beautiful video of the eruption yet", from a documentary team filming in the evening: