For the past week, geologists have been watching Iceland's massive Bárðarbunga volcano closely. There have been thousands of earthquakes in the surrounding area, a sign that magma is shifting around.
So far, there have been no actual eruptions — despite a false alarm this past weekend. But given that an eruption has the potential to spew plenty of ash into the atmosphere and disrupt flights across the northern Atlantic, Iceland is still on high alert.
For now, we're still waiting: The Icelandic Meteorological Office (IMO) recently downgraded Bárðarbunga from code "red" (which means an eruption is occurring or is imminent) back to code "orange" (which means the volcano is at increased risk of eruption).
The Bárðarbunga volcanic system lies under the 500-meter thick Vatnajokull glacier in the center of the island. Eruptions can occur from the volcano's massive caldera, from its sides, or from the surrounding fissures.
Back on August 16 and 17, scientists first started detecting thousands of earthquakes in the area. The earthquake swarms were migrating northeast — a sign that magma was on the move, flowing through fractures in the ground and forming a stretch of newly formed rock known as a dike.
On August 23, seismic measurements had initially suggested that the magma was finally migrating to the surface and that a lava eruption was occurring. But the Icelandic Meteorological Office later noted that this was a false alarm. If the magma had reached the surface, they argued, we likely would've seen signs that it was melting the glacier from below — creating floods, for instance. So the agency soon walked back the eruption alert.
So what's next?
There's still a possibility of an eruption: The earthquakes keep migrating, and by August 25, the agency noted that the dike had now extended more than 35 kilometers (20 miles) to the northeast of Bárðarbunga, stretching past the Dyngjujökull glacier:
The earthquake swarm is migrating northeast
All told, the dike now contains some 300 million cubic meters of magma, the IMO estimates. And at this point, the agency says, there are a few possibilities for how this could all play out:
1) The migration of magma could simply stop — and earthquakes would gradually cease. No eruption.
2) The dike could eventually break through the surface of the Earth's crust, leading to a lava eruption (most likely near the northernmost tip of the dike). "This would most likely produce an effusive lava eruption with limited explosive, ash-producing activity," the IMO notes.
3) Alternatively, the dike could erupt somewhere underneath the glacier. This could be far more dramatic. The combination of lava and ice can produce a steam explosion that would send ash billowing high into the atmosphere. Or, alternatively, the lava could melt the ice and produce serious flooding in Iceland's Jökulsá á Fjöllum river that extends to the north.
A lot depends on how much magma erupts, how quickly it erupts, and how much ice is above the eruption. The last big subglacial eruption took place in 2011, at the nearby Grímsvötn volcano. That eruption broke through the ice, spewed ash 20 kilometers into the air — and disrupted air travel for days.
Volcanic ash, which contains glass and pulverized rock particles, tends to be bad for airplane engines: the particles can erode the engine compressor or even solidify on the turbine blades, blocking the engine. Back in 2010, after the Eyjafjallajökull eruption spewed ash for miles into the atmosphere, airlines across Europe grounded flights for six days. In the years since, however, airlines have relaxed their policies on flying through ash — and it's unlikely that any eruption today would be as disruptive as in 2010.
For now, however, geologists are still waiting to see what will happen.
How to track the volcano
The Icelandic Met Office has been offering daily — and sometimes more than daily — updates on the volcano. There are also frequent English-language updates from the Icelandic newspaper Morgunblaðið.
On top of that, there are plenty of volcano experts on Twitter who are watching the eruption closely — including Dave McGarvie, Gisli Olafsson, and Erik Klemetti. Journalist Alexandra Witze has been tracking Icelandic volcanoes for a long time and is definitely worth following. And John Stevenson has done a lot of excellent work on the impacts of volcanic eruptions on aviation.