select search filters
briefings
roundups & rapid reactions
Fiona fox's blog
Experts comment on the science of flight safety and volcanology, and provide answers to questions from Channel 4 News viewers.
Science of flight safety:
Chris Yates, Aviation Consultant, said:
“The ICAO’s International Airways Volcanic Watch Operations Group (IAVWOPSG) states: “There is no definition of a safe concentration of ash for different aircraft, engine types or power settings.”
“The ICAO regulation that has prompted this widespread grounding is from experience gained from over 80 incidents between 1980 and 2000 and computer modelling/best guestimate. The airline industry will know this very well and are clearly making the argument that we are being over cautious in grounding all flights.
“Whilst it remains possible to find clear air up above us this doesn’t necessarily mean that there are no pockets of high concentrations of ash at the various flight levels though. I would therefore suggest it’s better to err on the side of caution.”
Stewart John, Fellow of the Royal Academy of Engineering and past President of the Royal Aeronautical Society, said:
“There is no real alternative for assessing the safety of flying without doing test flights. If the situation is desperate then a pilot will know almost immediately as it would be like flying through a sandstorm and the windscreen would be quickly abraded. That’s not the question being asked here though; the dust is so fine that it’s like talcum powder so the issue is of accumulated damage following a few hours of flying.
“Doing the tests is a bit like catching a butterfly in a net, you have to scoop in the air at 500mph and with all the heat of the engines that turns the ash into flecks of molten glass. Afterwards flight engineers have various ways of checking what damage has accrued such as using a borescope to assess the damage to air filters and turbines.
“Unfortunately there’s no real way of checking the build-up of damage in mid-flight and it really has to be done with a plane as you have to get the important factors of speed (up to around 500 mph) combined with the dust and the heat of the engines.
“The airlines are doing the responsible thing at the moment, but we really do need to start thinking of ways round this as we don’t know how long the problem is going to last. I have been asked about planes flying at different heights but this isn’t really a solution. Civil aircraft attain a maximum height of about 40,000 feet and their engines operate optimally at these heights. For every drop of 5,000 feet below this a plane uses about 5-6% more fuel, which is obviously a large amount on a long flight. But just as importantly, you could think that you’re safe flying along at 20,000 feet rather than up at 40,000 where the ash is, only to find that the wind has suddenly dropped and the ash is now at 20,000 feet. It would be a false sense of security so it really is vitally important that test flights are done that cover the entire spectrum of flight patterns.”
The volcano:
Dr John Murray, Senior Research Fellow, Dept Earth Sciences, The Open University, said:
“Contrary to what I said earlier, today the ash has significantly diminished and the ice over the crater itself has melted. This is the stage we have been waiting for: the phreatomagmatic activity (steam explosions due to water being trapped within the erupting lava) will have virtually ceased, and the activity has changed to lava outpouring. Ash may resume at any time, but it is likely to be less pronounced and prolonged than before.
“Hopefully this means that aircraft will be able to fly again shortly, though the meteorologists will have more information on that. The ash is fine grained, so it will take a while to fall to earth, though I hope the met office will tell us this will happen over a wide area generally further south than the UK.
“The possibility of the activity spreading to the neighbouring Katla volcano is still there, but there are no signs of this happening at present.”
Dr Dave McGarvie, Volcanologist, The Open University, said:
“Yesterday, 18 April, the plume stayed ‘low’ as it was not detected by the radar at Keflavik airport in Iceland. This radar only detects plumes above about 8 km (10,000 feet). Today, 19 April, the plume can be seen (on webcam) to be at low altitude (probably less then 2 km high) and streaming downwind from the vents.
“A tentative interpretation of this is either that the eruption is waning (i.e. lower mass discharge rate), or that there is minimal interaction with ice in the crater and so there is less fragmentation of magma leading to a lower and less buoyant eruption cloud. Visual observations during the day will help us understand what’s going on. But I am mindful of the fact that during the 1821-23 eruption there were periods (weeks-months) when the eruption died down and then started again.
“At the end of the day we have been extremely fortunate in the UK and western Europe to have avoided this disruption for so long. It was inevitable that this would happen, as Iceland has an eruption every 5 years or so. It just so happens that those that have erupted in the past 60 years have not affected us to this extent. But there are plenty of volcanoes that can erupt in a similar (or larger) fashion to Eyjafjallajokull. My sources in Iceland tell me that Hekla has been ‘full’ for months now. And though its recent eruptions have not affected the UK, future ones might well do so.”
Dr David Rothery, Dept of Earth & Environmental Sciences, The Open University, said:
“Webcam images at dawn 05:00 BST) this morning reveal a change in character of the summit eruption at Eyjafjallajokull. Small individual explosions could be seen, throwing blocks of incandescent molten lava onto the crater rim. Ash was still being produced, but was dispersing downwind at the altitude of the summit (about 1600 m). There was no high ash column rising above the vent. IF this situation persists, then the high altitude ash cloud will be starved of fresh ash, and will eventually disperse.
“What has probably happened inside the volcano, is that meltwater from the ice-cap is no longer able to leak into the magma conduit, where it has been the main driving force for the explosive expansion that has hitherto (since Thursday) been responsible for the eruption column.
“There is no guarantee that the situation will not revert to what was happening Thursday-Sunday, but there are grounds for cautious optimism.”
Q&A between Channel 4 viewers and some of our experts:
Dr John Murray, Senior Research Fellow, Dept Earth Sciences, The Open University, said:
“Today the ash has significantly diminished and the ice over the crater itself has melted. This is the stage we have been waiting for: the phreatomagmatic activity (steam explosions due to water being trapped within the erupting lava) will have virtually ceased, and the activity has changed to lava outpouring. Ash may resume at any time, but it is likely to be less pronounced and prolonged than before.”
Dr Dave McGarvie, Volcanologist, The Open University, said:
“Once the highly explosive activity that is generating the very small particles of ash has ended, then perhaps 3-4 days. Maybe less if the wind steers the ash cloud past the UK.”
Dr. Grant Allen, Centre for Atmospheric Science, University of Manchester, said:
“No, for two reasons. Firstly, the ash is slowly descending and Lidar plots recorded around the UK show that the plume is ubiquitous between 2 and 7 km altitude (and occasionally higher in places). Below 2 km the ash is very quickly caught in the turbulence of the surface boundary layer and deposited to ground though jet aircraft are not permitted to fly lower than 2 km due to surface hazards. Secondly, it is not fuel efficient for aircraft to fly lower than 35000 ft on long haul flights – for example, aircraft simply could not carry enough fuel for transatlantic flights if they flew at less than 5 (~15000 ft) km altitude. Furthermore, our knowledge of the 3-dimensional picture of the plume is too poor to accurately predict or observe such as to enable complex flight plans for aircraft to be developed in a timely fashion.”
Dr John Murray, Senior Research Fellow, Dept Earth Sciences, The Open University, said:
“Aircraft cannot avoid ash at lower altitudes. It all falls to the earth in the end, and the ash was already evident on my daughter’s car windscreen yesterday (see enclosed photograph).”
Dr Dave McGarvie, Volcanologist, The Open University, said:
“No, because the ash is in the lower atmosphere already and slowly drifting down towards the surface. [But if we had better ash-detecting radar that could give real-time 3D imaging of the ash cloud, we could perhaps identify low-risk corridors through which aircraft could fly in relative safety. This is not possible at the moment.]”
Dr Michael J. Branney, Senior Lecturer in Volcanology, Department of Geology, University of Leicester, said:
“Aeroplanes may be able to avoid the ash if they fly at higher or lower altitudes but this particular ash cloud presents two problems. Firstly, the cloud is being blown across the ascent and descent routes of northern Europe, where there are many international hubs. Therefore planes cannot pass through it as they ascend or descend in order to land and take off. Secondly, the ash cloud is a very broadly dispersed, and this would compromise for long stretches of the flight, the opportunity for planes to change their cruising altitude, as they commonly do in order to avoid adverse weather conditions such as turbulence. That’s not good. Finally, ash falls out from ash clouds and so there is likely to be ash at lower altitudes than the cloud, particularly if where moisture helps bring the ash down – moisture in the atmosphere can cause ash particles to stick together forming aggregates that may then fallout quicker as they have a larger size/settling velocity than the individual particles.”
Dr. Guy Gratton, Head of the Facility for Airborne Atmospheric Measurements, Cranfield University, said:
“No, a very large proportion of the ash, and much of that very fine, is between the surface and 6,000ft. Typically light aeroplanes fly at 1,000-3,000ft, and airliners at 20,000-40,000ft.”
Dr Colin Macpherson, Department of Earth Sciences, Durham University, said:
“As yet, there are no direct measurements of the CO2 emission rate for Eyjafjoll eruption. There are preliminary estimates for SO2 emission and CO2/SO2 ratios for the recent eruption of Fimmvörduháls on the flanks of Eyjafjoll1. The composition of the Ejyakjoll eruption is somewhat different (more silica-rich2) than Fimmvörduháls, but assuming similar gas characteristics we can estimate the CO2 flux from Eyjafjoll.
SO2 output of Fimmvörduháls eruption1: 3000 tonnes/day
Relative CO2 content of Fimmvörduháls eruption1: <15%
Relative SO2 content of Fimmvörduháls eruption1: <3%
“This provides a rough maximum estimate for the CO2 : SO2 ratio of ~ 5 : 1. Therefore, the CO2 flux calculated for Fimmvörduháls is 15,000 tonnes/day. This figure is currently circulating on the internet as the same rate for Eyjafjoll. But, the Icelandic Institute of Earth Sciences2 estimate that the magma flux rate over the first 72 hours of the Eyjafjoll eruption was 10 to 20 time higher than that of Fimmvörduháls. Taking the lower limit of 10 times the Fimmvörduháls volume then the CO2 flux of Eyjafjoll would be 150,000 tonnes/day. Until it is possible to accurately constrain the volume of magma erupted from each volcano and to verify whether there are significant differences in the composition of Fimmvörduháls and Eyjafjoll gases, this estimate is subject to very large uncertainty, probably one order of magnitude. However, the CO2 content of the magma inferred from the calculation is 0.25 weight percent, which is reasonable for moderately degassed Icelandic magma.
“There are very large uncertainties on this, because all the observations are preliminary and there are significant assumptions. But I think that it is the best we can do until the volcano settles and direct measurements can be made. This estimate is about 40% of the daily emissions from European aviation.”
Dr Peter Abbott, School of Geography & Geosciences, University of St Andrews, said:
“I saw this interesting figure on the internet that may be useful. Details of who produced it are on the figure. It was published on the day of the eruption, but I think it nicely demonstrates that the CO2 emissions of the eruption are small fry compared to the planes!” http://www.informationisbeautiful.net/2010/planes-or-volcano/
Dr Dave McGarvie, Volcanologist, The Open University, said:
“As Icelandic volcanoes don’t erupt much CO2 there’s not much CO2 coming out of this particular volcano. We’d need a detailed gas analysis from the eruption site before we could start the number crunching to answer this great question!”
Dr Michael J. Branney, Senior Lecturer in Volcanology, Department of Geology, University of Leicester, said:
“I don’t know the present balance. But of course, there’s no way to prevent volcanoes producing CO2, but in reducing flights we have reduced our carbon dioxide production.”
Prof Jon Davidson, Chair of Earth Sciences, Department of Earth Sciences, University of Durham, said:
“The eruption is very ordinary and unremarkable. It’s the fact that it happens to be combined with local weather systems which push the ash over N European airspace.
“In other parts of the world ash has certainly interrupted air traffic (e.g. Ruapehu, New Zealand), but in most cases eruptions have not been sustained for long periods and winds have not dispersed them into critical airspaces. Remember that the period of widespread commercial flying is less than 50 years (so we haven’t yet encountered anything like the diversity of volcanic eruption possibilities that might be produced), and its only in the last 30 or so years that we have recognised volcanic ash as a potentially serious threat to aviation (the first international symposium on volcanic ash and aviation safety was in 1991)….AND there have been several incidents of aircraft flying into ash plumes (e.g. Indonesia, Aleutians, with thankfully no casualties).”
Dr Michael J. Branney, Senior Lecturer in Volcanology, Department of Geology, University of Leicester, said:
“It depends where the wind blows the ash. In today’s case the ash cloud is being blown in a broad plume over areas with densely spaced airports and several major international hubs. In some other parts of the world, ash plumes may only blow across one or two airports (e.g. Anchorage, Alaska) which then close temporarily, and passing aircraft can sometimes be re-routed to avoid the ash cloud. In some other parts of the world the ash plume may blow largely across the ocean, where it gradually disperses. In contrast, this cloud is blowing across a large populated land mass.”
Dr. Grant Allen, Centre for Atmospheric Science, University of Manchester, said:
“Aircraft contrails actually warm the Earth’s surface, not the other way around. Due to their position in the upper troposphere, contrails act to trap infrared radiation in the lower atmosphere and their net effect over the day/night cycle is to warm the surface. Volcanic ash, however, always acts to cool the surface. Dust and sulphur dioxide which is deposited in the stratosphere reflects solar shortwave radiation to space and also absorbs/scatters it in the stratosphere before it reaches the surface, thus reducing the energy budget at the Earth’s surface. Furthermore, ash in the stratosphere does not trap infrared radiation and re-emit it back into the troposphere. In summary, if continued for many weeks, the ash will have a cooling effect on the Northern Hemisphere which would last for many months/years, similar to the observed effect of the Mt. Pinatubo eruption in 1991 which is documented to have cooled the Earth’s climate for several years after the eruption.”
Prof Jon Davidson, Chair of Earth Sciences, Department of Earth Sciences, University of Durham, said:
“The ash will not be a long term problem – more likely the SO2 which forms aerosols and could block some incident sunlight (but even so this is still a minor eruption and effects will be negligible to now).”
Dr. Guy Gratton, Head of the Facility for Airborne Atmospheric Measurements, Cranfield University, said:
“Nothing, the main player is the weather system, over which we have no short term control.”
Prof Jon Davidson, Chair of Earth Sciences, Department of Earth Sciences, University of Durham, said:
“Nope. What we could hope for is a way to better track the ash and to determine its density – and know how the ash density maps onto hazard for aircraft, which I don’t think we do.”
Dr Michael J. Branney, Senior Lecturer in Volcanology, Department of Geology, University of Leicester, said:
“Not easily. Volcanic activity cannot be modified by human intervention any more than storms.”
Dr John Murray, Senior Research Fellow, Dept Earth Sciences, The Open University, said:
“Yes, definitely!!!”
Prof Jon Davidson, Chair of Earth Sciences, Department of Earth Sciences, University of Durham, said:
“See the links here for health advice: http://www.ivhhn.org/“
Dr. Guy Gratton, Head of the Facility for Airborne Atmospheric Measurements, Cranfield University, said:
“At present, the UK CAA is in the lead of trying to understand any potential public health risks. Once we’ve got samples from the research aircraft, they’ll be being analysed by an appropriate public health laboratory.”
Dr Michael J. Branney, Senior Lecturer in Volcanology, Department of Geology, University of Leicester, said:
“I shouldn’t worry about playing outside in the UK, with the exception that I understand that some experts have suggested that folk with respiratory conditions (e.g. bronchitis, asthma) may be advised to carry their medication to hand, and remain indoors if they can see falling ash or smell or taste acid or sulphurous smells. However, the concentration of ash is likely to be very low at this distance from the volcano.”
Dr. Grant Allen, Centre for Atmospheric Science, University of Manchester, said:
“Possibly, but only if a) the volcano continues to erupt and emit ash due to its contact with water and ice; and b) we continue to see high pressure weather regimes over the East Atlantic as we have now, which acts to draw air down from Iceland over the UK.”
Prof Jon Davidson, Chair of Earth Sciences, Department of Earth Sciences, University of Durham, said:
“Depends on two “weathers”- whether the eruption continues and how its intensity (and capacity to fragment and carry ash upwards) varies, and the weather as in the directions that sash is dispersed.”
Dr Dave McGarvie, Volcanologist, The Open University, said:
“Depends on what happens at the eruption site. The conditions that produced the fine-grained ash that is causing the airspace no-fly problem involve an energetic eruption interacting with ice (and its meltwater) and in doing so creating steam explosions which in turn fragment the erupting magma into very small particles of ash that can be transported long distances. Once interactions with ice/meltwater cease the steam explosions cease then so will the production of the very small particles that’s causing the problem. It is normal for eruptions to start energetically (i.e. explosively) and then to become quieter with time, at which point lava flows are effused. So this is likely to happen with this eruption, possibly right now or within a few days. But – and it’s a big but – eruptions like this can have a number of cycles, and so we could see another cycle start with a renewal of explosive activity at any time. Whether this will be as problematic as the current eruption will depend on how energetic the eruption is, the type of magma that erupts and how fast it erupts, and how much interaction there is with ice in the crater. And of course even if there is another eruptive cycle the winds could steer the ash in a direction away from the UK. Yes – lots of variables! But that’s part of the fun and challenge of working on volcanoes.”
“It may be, if the eruption continues in its current style, in which case as weather conditions shift the path of the ash cloud over different regions from time to time it may affect different sectors of airspace. However, it is quite common that this type of eruption becomes less explosive with time, for example if the access of glacier ice and meltwater lessens, in which case less fine ash may get ejected into the atmosphere, and the hazard will reduce to more local (southern Icelandic) proportions.”
Dr. Guy Gratton, Head of the Facility for Airborne Atmospheric Measurements, Cranfield University, said:
“It would make no difference because the lower planetary boundary layer is already (a) very turbulent, and (b) where the large proportion of ash is.”
Dr Dave McGarvie, Volcanologist, The Open University, said:
“You might just get some ash on your face.”