Race to protect jets from looming ash cloud threat "Whether they will erupt tomorrow or in five years, we do not know," he said. There is no question whether they will erupt or not, the question is how big will the eruption be and how long will it last? Katla - which lies beneath a glacier like Eyjafjallajökull - is experiencing seismic activity and is bulging up at the surface while Hekla has grown to the height it was when it last erupted in 2000. They could erupt with a mere few hours warning, Professor Thordarson said, and it is believed they could create plumes 18 miles high and impact on European airspace for several days if the eruption coincides with north-westerly winds. After Eyjafjallajökull erupted the Institute of Earth Sciences collected the ash - which poses a threat to plane engines - from beneath the glacier. It will now be used to test the new technology on two airliners by Nicarnica Aviation, easyJet and Airbus. The technology should allow the aircraft to detect silicate, the main component of the ash, using infra-red sensors, from 30km - therefore giving the pilot time to change course. The August experiment has been timed to coincide with the alignment of the Seviri and Calypso satellites, which may be able to confirm the accuracy of the technology. The technology, invented by Fred Prata, of the Norwegian Institute for Air Research, has already been successfully tested on Saharan dust clouds and last summer Airbus tested for false alarms using water vapour. There are fears that it may not be certified in time for the next eruption.