Last April's decision to close much of Europe's airspace as a result of the volcanic ash that spread across the continent following the eruption of Eyjafjallajökull in Iceland was "well grounded", according to a new scientific study which also recommends a protocol to assess the risks to aircraft from similar events in the future.
The study, carried out by researchers at the University of Copenhagen and the University of Iceland and published yesterday in the Proceedings of the National Academy of Sciences, analysed particles collected immediately after the Icelandic eruption.
It concludes that the particles could have led to engine failure as well as abrasion to an aircraft's exterior because they were sharp enough to sandblast aircraft windows, bodies, wings and engines.
"There is no doubt from the shape and size of the particles that they would have been a danger to aircraft and melted quickly in a jet engine, causing it to fail," says the study's co-author Dr Susan Stipp, adding that "what was unknown was when to re-open".
This was down to guesswork, with aviation authorities "acting blind", which is why Stipp and her colleagues "worked in the evenings and at weekends" to come up with a protocol.
The size, shape and hardness of volcanic ash particles are the "key parameters" for assessing the risk to aircraft of similar events in the future, says the study.
Instruments to determine these parameters are available in earth and materials science laboratories. BET surface area measurements provide the size data, while scanning electron microscopy (SEM) analysis provides the shape data. X-ray diffraction (XRD) calculates mineral composition to determine the hardness and melting temperature of the particles.
"Together with estimates of the mass of ash produced, plume height, grain size distribution and the dispersion rate, these data would provide input for modelling to predict the hazard level for aircraft," says the study. Other data, such as wind speed, would need to be provided for modelling purposes.
In order to access information quickly following a similar event in the future, "aviation authorities would need to make contact with a lab or two" in advance, says Stipp.
"It doesn't have to be our lab - it could be anyone with these instruments." If arrangements with laboratories are made in advance, results from volcanic ash samples could be available "within several hours". Therefore, "to be effective, aviation authorities would need to set this up ahead of time", says Stipp.