It is partly the fineness of the Chilean volcanic ash which is posing problems for aircraft safety in distant places, including New Zealand, University of Otago vulcanologist Associate Prof James White says.
Chilean volcanoes had erupted several times in recent decades, but usually had posed few problems for distant countries because the ash emitted had not been sufficiently fine to travel such long distances, he said.
A different part of the Puyehue-Cordon Caulle volcano in Chile had previously erupted in 1960.
Prof White, of the university geology department, said the recent volcanic ash problems, which had restricted aircraft movements in Australia, New Zealand and on transtasman routes, also reflected the way in which an increasingly complex and technological society could also become more vulnerable.
Ben Liley, an atmospheric scientist at the National Institute of Water and Atmospheric Research station at Lauder, in Central Otago, said there were grounds for cautious optimism that the fine ash might not prove too disruptive for New Zealand aviation.
Staff at Lauder had been monitoring the ash movements, using light detection and ranging (Lidar) equipment, since last Saturday.
The fine ash particles had generally been travelling at altitudes of about 10,000m and above.
This meant it had usually been possible for Air New Zealand passenger jets to operate safely below the usual 10,000m cruising altitude.
The ash particles were often travelling in the lower part of the stratosphere, where they were trapped in a band of cold air, and tended to travel horizontally rather than up and down, he said.
Civil Aviation Authority meteorological manager Peter Lechner said the Niwa data from Lauder was proving "invaluable".
The fact that the ash particles had often been trapped in the stratosphere provided grounds for cautious optimism that future air travel disruption might not be too severe.