An abnormally high fraction of the ash particles spewed skyward by Iceland's Eyjafjallajökull volcano last April were small and sharp and therefore posed high risks to airplanes and human health, a new study suggests. That means the 7-day shutdown of much of Europe's air traffic ordered by civil aviation authorities, which affected 10 million passengers and cost between €1.5 billion and €2.5 billion, was likely worth it.
Eyjafjallajökull began erupting on 20 March 2010. For the first couple of weeks, lava oozed from a fissure on its ice-free flank, and the resulting ash plume was anything but impressive. On 14 April, however, molten rock began flowing from the ice-filled crater at the mountain's peak, and the eruption became explosive. The resulting plume of ash wafted southeast over Europe and triggered the largest disruption of the continent's air traffic since World War II.
The debate about whether and when to shut down air traffic, as well as when to reopen the skies to aircraft, was largely a matter of economics versus safety. "It was a matter of losing big bucks versus losing people," says Susan Stipp, a geochemist at the University of Copenhagen in Denmark. Tiny particles of ash sandblast the windows and flight surfaces of any aircraft passing through even a diffuse volcanic plume, thereby blocking a pilot's view forward. What's more, the particles melt when exposed to the hellish temperatures inside a jet engine and can stick to turbine blades, disrupting airflow and stalling the engines-and possibly causing the plane to crash.
Eyjafjallajökull's ash was particularly hazardous, according to an analysis reported by Stipp and colleagues online today in the Proceedings of the National Academy of Sciences. The steam explosions that resulted when water from a melting glacier met molten lava shattered the cooled, solidified lava into tiny knife-edged shards. Although less than 2% by weight of ash particles spewed during a typical eruption measure less than 10 micrometers across, more than 20% by weight of Eyjafjallajökull's early-stage ash fell below this unhealthful threshold. This powdery ash is particularly susceptible to melting quickly inside a jet engine, the researchers note. It can also be readily breathed deep into the lungs of humans living downwind of the volcano.
The sharp edges on Eyjafjallajökull's ash particles didn't wear away even when large numbers of ash particles were swirled in a beaker of water for 2 weeks, a sign, Stipp says, that the powdery ash could have remained a risk to aviation as long as it remained airborne.
The new research "is a very nice piece of work," says Kirk Nordstrom, a hydrogeochemist at the U.S. Geological Survey in Boulder, Colorado. "These particles are particularly abrasive, and they have more ability to damage aircraft than most people realize."
Moreover, Eyjafjallajökull's early-stage ash boasted a greater surface area upon which noxious constituents of the volcanic plume--including fluorine, chlorine, and sulfur dioxide--could attach. The team's lab tests suggest that the powdery ash had about 10 times the area found on a similar-sized sample of typical ash. Although most scientists presume that those harmful gases are concentrated near the volcano, the new findings hint that in some cases, particularly when glacial meltwater interacts with lava to produce exceptionally fine ash, the hazards could be transported long distances, Nordstrom says.
Stipp and her colleagues suggest that ash falls from this eruption weren't a large threat to Europe, but the ones in Iceland were certainly hazardous to humans and to grazing animals that might have ingested substantial amounts of the sharp-edged grit.