Volcanoes and Winds: 2010 Iceland Edition

Hello all! Today we are travelling back in time to 2010.
Before I get into why we’re discussing this particular year, let’s talk about volcanoes. I could say many things about volcanoes, but for today’s post, I’m going to talk about volcanoes throwing up ash into the atmosphere. It makes for amazing photographs…and dangerous conditions for aircraft. Jet engines and volcanic ash are not friends. Jet engines can currently only handle a small concentration of ash in the air. In 2010, when a volcano in Iceland erupted, ash disrupted air travel in several countries, which in turn created a ripple effect to wreak havoc on even more air travel. Over several countries, a total of over 100,000 flights were grounded.
That brings us to today’s article, written by M. J. WoodhouseA. J. HoggJ. C. Phillipsand R. S. J. Sparks, published in American Geophysical Union’s publication Journal of Geophysical Research: Solid Earth, in 2013, with the title “Interaction between volcanic plumes and wind during the 2010 Eyjafjallajökull eruption, Iceland“. Now if the name of that volcano scares you then…well…I can’t blame. Unless you happen to be from Iceland (which to date, according to my WordPress stats, none of my readers have been) or happen to be familiar with the language, that name is terrifying. I think it is pronounced ay-ya-fyet-la-yur-kull. Ish.
For the sanity of myself typing–and of your reading–I am just going to call it ‘that volcano’ or ‘the volcano in question’ or some other name-avoiding phrase.
The volcano in question is on the south coast of Iceland, stands 1666 meters (just over a mile) above sea level and has a caldera 2.5 kilometers (about 1.55 miles) across, covered in ice 200 to 400 meters (656 to 1312 feet) thick. When it first started erupting on April 14th, 2010, the ice quickly melted (it is a volcano, after all) and a plume, without all that much ash in it, went skywards. Later that day, the plume was much more ash-rich.This continued until the 18th of April. The volcanic activity then lessened until May 5th, when it picked back up again. On the 18th of May it decreased again, continuous activity ceasing three days later. Some of the ash was carried long distances by the wind, though most of it fell near the volcano.
As you can see here, the ash from Eyjafjallajökull was moved over several countries and grounding flights. Image credit: NASA Earth Observatory
As you can see here, the ash from Eyjafjallajökull was moved over several countries and grounding flights. Image credit: NASA Earth Observatory
Trying to figure out how ash will act in the atmosphere (important for finding where it is safe or unsafe to fly) depends mostly on two things; the source mass flux and the plume height. The source mass flux is the amount of mass (i.e. the weight of ash and gases in the plume) coming from the volcano over time. This is not something that can be directly measured, but can be determined by looking at related data. The plume height is just as it sounds. At some point, the density (mass per volume) of the plume is going to equal that of the surrounding atmosphere, and will thus level out. It will go slightly past this simply due to inertia, then fall back down to this same-density level, known as the point of neutral buoyancy.
Using a whole lot of math and previously compiled datasets, the authors modeled a general volcanic plume, including the mixing of the surrounding air through eddies at its edges and the wind. The wind, as it turned out, played a large role in the plume height. Without any wind, the plume rises straight up; as the wind increases, the plume bends over to the side more and more. If the wind was faster than about 30 meters per second (67 mph) the plume height would not reach 15 kilometers (9 miles).
With this model in place, the authors could then apply the various local meteorological conditions, such as wind speeds, pressure, temperature, and relative humidity. There are not local observations taken at the volcano, but Keflavik International Airport lies 155 kilometers (96 miles) away, and this was a good approximation of what conditions at the actual eruption site were expected.
On April 14th, the plume was over 8 kilometers (5 miles) tall, shorter the next two days (5-7 kilometers, or 3 to 4 miles) when the wind was stronger, and back up the 17th when the weather changed again. There are other factors, but wind speed is the main one.
There are basically two ways of explaining this change in plume height. One is that the source mass flux changed dramatically (more than a factor of ten)–which there is no other suggestion of–or that the plume height is impacted noticeably by the wind speeds while the mass flux stays more or less constant. The wind is the most logical explanation. This does have important impacts–if one calculates mass flux without taking the wind into account, the result may be grossly underestimated. This in turn would affect the concentration expected in the air which in turn becomes a safety issue for aircraft. Considering this eruption grounded 19,000 flights per day at its peak, the new relationship between plume height and wind speed is going to be a helpful step in continuing research.

 

Bibliography
How the 2010 ash cloud caused chaos: facts and figures“. The Telegraph. 24 May 2011. Web.
A short page from which I took stats; also has a fantastic image of the discussed volcano during its eruption.
National Air and Space Administration Earth Observatory. Eruption of Eyjafjallajökull Volcano, Iceland. NASA Earth Observatory. April 16 2010. Web.
The source of the image used in today’s article.
Woodhouse, M. J., A. J. Hogg, J. C. Phillips, and R. S. J. Sparks (2013), Interaction between volcanic plumes anwind during the 2010 Eyjafjallajökull eruption, Iceland, J. Geophys. Res. Solid Earth, 118, 92–109, doi:10.1029/2012JB009592
Today’s main article.

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