August 23 – Bardarbing, Bardarbang, Bardarbunga!

Today’s factismal: The Bardarbunga volcano in Iceland has begun to erupt!

If you are a geologist, these are exciting times. Not only do we finally have a theory that explains how mountains and volcanoes form, we’ve got all kinds of instruments that helps us gather the data we need to test the theory and make it better. (That’s what scientists do, you know – we hatch ideas, carefully feed them on data until they become hypotheses, and then test them with yet more data leaving only the strongest behind as theories. And then we start all over again with the ideas that the theory spawns.)  Thanks to the Cold War, we’ve got seismometers located all across the globe; though they were put there to detect atomic bomb tests, they also record earthquakes which helps us learn more about the inside of the Earth. And thanks to the Cold War, we’ve got satellite altimetry across the globe; though it was created to help us detect bomb craters, it also helps us to measure how the Earth’s surface tilts and where things in the upper crust are moving. And thanks to the Cold War, we’ve got satellites that measure the change in gravity; though they were created to help track submarines (and to make our missiles more accurate), they also tell us where materials in the Earth change density. And, thanks to the Cold War (do you detect a theme here?), we’ve got GPS; though it was created to help the military move around, it also helps us track the movement of continents and mountains. And all of that data has lead in turn to a deeper understanding of the Earth.

And though a lot of that understanding is purely academic, such as the discovery that there is the equivalent of three ocean’s worth of water stored in the minerals of the Earth’s mantle, a surprising amount of it is very practical indeed. Understanding how the plates move around on the Earth has led to discovering new deposits of gold, silver, and diamonds (not to mention oil and gas), and to learning which areas are most at risk for earthquakes and volcanoes. Even better, it has helped us learn how to predict volcanic eruptions (we’re still working on predicting the timing of earthquakes). One of our earliest successes was Mt. St Helens; the scientists in the area were able to predict the eruption and save the life of everyone who was willing to evacuate. And today we have another example of that science at work in the eruption of Bárðarbunga (Bardarbunga {bar-dar-BUNG-ah!} to everyone but the Icelandics).

Like Mt. St Helens, Bardarbunga is a stratovolcano. That means that it is a tall, cone-shaped volcano made up of alternating layers of ash and lava fed from a subterranean magma chamber that sometimes erupts explosively (creating the ash) and sometimes erupts more passively (pouring out the lava). These are among the most common volcanoes on Earth and create some of the most spectacular eruptions (e.g., Krakatoa) as well as some of the least interesting ones (e.g., Stromboli, “the lighthouse of the Mediterranean”). Where Bardarbunga and Mt. St Helens differ is that Mt. St Helens is created by plate tectonics and Bardarbunga is created by a mantle plume. (That’s part of the “testing the theory” we discussed.) Where plate tectonic volcanoes are formed when subducting plates release a little water that stimulates magma production which then creates the volcano, mantle plume volcanoes are created by extra-light material coming from deep within the mantle. We’re still arguing over why mantle plumes should exist, as well as how many of them there are; everyone agrees on Iceland (where Bardarbunga is) and Hawai’i, but that’s it.

Location of earthquakes around the Bardarbunga volcano (Image courtesy aaaa)

Location of earthquakes around the Bardarbunga volcano
(Image courtesy Iceland Met Office)

The number of earthquakes per day (Image courtesy Iceland Met Office)

The number of earthquakes per day
(Image courtesy Iceland Met Office)

 

One thing that we’re not arguing over is that Bardarbunga is erupting. Starting about two weeks ago, seismologists noticed that the number of earthquakes, and especially the shallow earthquakes, in the area had taken a steep jump upward. Because adding magma to a region “stretches” the surface material, you always hear creaks and groans in the form of small earthquakes when it happens. In addition, the geophysicists in the area using GPS had noticed that the ground was starting to tilt; that’s another strong hint that there was magma moving into the area. And so Iceland raised the eruption threat to “Orange” (right below “Red” or “Watch out – the lava’s a’coming!”).

Today, the eruption threat was raised to Red as a small plume of ash and smoke was seen coming from the ice covering Bardarbunga. And that is the second important way that Bardarbunga differs from Mt. St Helens. Where Mt. St Helens had a light dusting of snow on its top, not more than a hundred feet thick, Bardarbunga is buried beneath a glacier; this is even more impressive when you realize that the volcano’s top lies 6,600 ft above sea level. The Vatnajökull (vat-na-JOKE-ull) glacier covering the volcano averages 1,300 ft thick and so forms a most excellent plug over the volcano. And that means that we may get an great view of a subglacial eruption!

Satellite image of Iceland; Bardarbunga is in the middle of the large chunk of ice (Image courtesy NASA)

Satellite image of Iceland; Bardarbunga is in the middle of the large chunk of ice
(Image courtesy NASA)

When hot lava meets cold ice, several things, all of which are fascinating, happen. The heat from the lava can melt the ice, forming a subglacial lake that eventually breaks through and rushes downhill like a crazed wet, weasel; this “jökulhlaup” (“glacier run” {yokel-oop}) can carve valleys and denude meadows faster than a politician can pocket a bribe. If there is enough ash mixed in the water, it forms a lahar which is basically a mud flood moving sixty miles an hour and not stopping for directions;in 1985, a lahar killed 23,000 people in Columbia. If the lava is erupted more quickly than the water can drain, then the heat may cause the water to turn into steam creating a steam explosion. This can then fling pieces of lava as large as a house for miles around.

Even if none of these things happen, the volcano will still put out ash and carbon dioxide and other particulates. The ash can make flying hazardous as the sharp edges eat away at jet turbine blades and propellers and literally sand-blast windshields into opacity. It is for this reason that planes are directed to fly well away from any erupting volcano. The carbon dioxide may seem like a lot, but it is actually relatively little. If this is a typical volcanic eruption, then it will put out about 500,000 m3 of lava and will eject about 8,300 tons of CO2 into the atmosphere, along with 2,000 tons of SO2 and 6,300 tons of H2O. In comparison, a car emits about 5.5 tons of CO2 per year, so Bardarbunga will add less CO2 than the amount generated by Houston traffic over the length of the eruption. But the SO2 is particularly interesting. As Franklin suggested back in 1784, volcanoes can cool the planet. We are still arguing about how they do so, but we know that the SO2 plays a key part. It acts to reflect sunlight back into space, helping to cool the planet. But such effects are short-lived; when Pinatubo erupted in 1991, it cooled the Earth by nearly 0.7°F but temperatures were back to normal by 1993.

So right now we’ve got an erupting volcano with lots of potentially interesting effects. Grab the popcorn and stay tuned!

August 29 Update: The eruption has subsided and Iceland has reduced the threat level to “orange” (possibly dangerous but not certain).

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