Bardarbunga and SO2 emissions: comparison with Laki 1783

Bardarbunga spewing gas from Nature/News
Arctic-Images/Corbis

"Gas-spewing Icelandic volcano stuns scientists". So reads the headline in Nature/News on October 28. Bardarbunga, about 250 km from Reyjkjavik, has been erupting for over two months (see previous posts on this blog here and here). The reason that scientists were "surprised" is that they had been expecting Bardarbunga to mimic the 2010 Eyjafjallajokull eruption that spewed ash high into the flight paths of airplanes, and instead, they are getting lava flows and gas.

Over a period of about two weeks in August, magma moved underground (in a configuration called a dike by volcanologists) approximately 45 km to the edge of an ice cap. There it began erupting into a barren plane called "Holuhran". Along with the lava, SO2 has been erupting in such quantities that Austria is recording more sulphur in its air than anytime since the 1980's when industrial pollution was still at high levels in Europe.

NASA Earth Observatory image in early September

How much sulfur dioxide is being emitted? Estimates are about 35,000 metric tons (tones) per day, and the Nature/News article uses the comparison that this is about twice the amount spewing from all of Europe's smokestacks. In the town of Hofn, sulfur spikes as high as 21,000 micrograms per cubic meter have been measured, more than 40 times the recommend maximum 10-minute exposure of 500 micrograms per cubic meter, according to the WHO. Hofn lies southeast of Bardarbunga (about 250 km as far as I can estimate) across the entire expanse of Vatnajokull. In early September, people in Norway 800 miles away reported smelling sulfur from the volcano.

The eruption site is remote, winter is setting in making logistics difficult, and the darkness of winter at such high latitudes will limit the amount of data that can be collected. The limited ground observations will be supplemented by satellite observations.

In 1783-1784, a fissure eruption similar to this one, known as the "Skafta fires" or the 1783 Laki eruption, spewed forth about 14 cubic kilometers of lava, nearly 1 cubic kilometer of ash, 8 million tons of hydrogen fluoride, and 120 million tons of sulfur dioxide, producing the "Laki haze" across Europe.  In Iceland, this is known as the "Mist Hardships," killing 20-25% of the population by famine and fluoride poisoning, 80% of the sheep, 50% of the cattle and horses. It is speculated that the eruption weakened the African and Indian monsoons, causing low flow on the nile and a famine in Egypt that killed 1/6 of the population. In Europe, the weather became hot through the summer of 1783, the winter was also severe, and the weather disruptions continued for several years. In North America, the winter of 1784 was miserable, with the Chesapeake freezing over at Annapolus, the Mississippi froze at New Orleans, and there was ice in the Gulf of Mexico. Benjamin Franklin made observations of the fogs in Europe and in North America and speculated that it was due to Hekla in Iceland, not knowing about the Laki eruption.

Assuming that the 120 million tons of SO2 in the 1783 eruption was degassed uniformly over 8 months, the rate averaged about 500,000 tons per day. Ignoring the 10% difference between metric tons (tonnes) and short tons, the Laki degassing was about 15 times as intense as the Bardarbunga. The last event similar to the current eruption began in 1975, the so-called Krafla fires, and lasted until 1975. Freysteinn Sigmundsson, a volcanologist at the University of Iceland and co-leader of the FUTUREVOLC project, suggests that the current eruption could continue for months or years if, as it appears, magma deep in the crust is being tapped.