A history of ash clouds and aviation

During 2010’s Eyjafjallajökull eruption, as the planes stood on the tarmac, many people asked why this hadn’t happened before.  After all, Iceland’s volcanoes have been active since long before mankind took to the skies.  Well, there are three main reasons for this.  These are the volcanoes, the airline industry and flight safety regulations.  This post looks at how all three have changed since the Second World War.

The volcanoes

The orange areas in the barcode-like diagram below show all the periods in which volcanoes in Iceland were erupting.  The data came from the Global Volcanism Program.  It’s a fairly regular occurrence, as you can see.  On average, as I explained in my first ever volcan01010 blog post, there is an eruption in Iceland about every 5 years, with 3/4 of them being explosive.  The wind blows towards the UK about 1/3 of the time, so you could expect a direct hit from an ash cloud about once every 20 years.

The Surtsey and Krafla Fires eruptions stand out for their long duration.  Surtsey, in particular, is interesting because the eruption produced a new island in the north Atlantic, with ash-rich explosions driven by hot magma boiling the water of the ocean.  It lasted three and a half years.  What would happen if a similar eruption began now?

I’ve marked the three most powerful explosive eruptions, Hekla 1947, Eyjafjallajökull 2010 and Grímsvötn 2011, with bold lines.  These produced much more ash than the others.  It is pure luck that there was such a long gap between them.

The airline industry

The blue line shows the huge growth in the global airline industry over the past 70 years (averaging 5% per annum).  There were no transatlantic passenger flights at the time of Hekla 1947.  By 2010, there were 2.5 million passengers flying between London Heathrow and New York JFK per year.  The more planes that are flying around, the more chance there is that one will meet an ash cloud.  In the two most dramatic encounters (BA Flight 9 vs Galunggung, Indonesia and KLM Flight 867 vs Mt Redoubt, Alaska, USA) the ash caused the jet engines to fail.  This led to changes to flight rules described below.

An important point to note is that as society becomes more dependent on air transport, any disruption is going to be increasingly expensive.

Flight safety regulations

The near-miss ash cloud encounters led to the establishment of the International Airways Volcano Watch in 1987, and the process of designating regional meteorological  agencies as Volcanic Ash Advisory Centres (VAACs) began in 1990.  With no proper measurements of how much ash was safe to fly through, the guidance was to ‘avoid all ash’.  The final graph shows the period when these rules were in effect.

In much of the world, where planes can just divert around dangerous areas, the guidance worked well.  But when Eyjafjallajökull dispersed ash across much of NW Europe in 2010, closing the airspace of entire countries, it led to 95,000 cancelled flights and the massive global disruption that made the volcano infamous.

The Eyjafjallajökull eruption was the most ash-rich explosive eruption in Iceland since the rules were put in place, but it wasn’t the first time that Icelandic eruptions had affected flights.  The Hekla 2000 eruption damaged a NASA DC-8 aircraft that accidentally flew through the plume, and the Grímsvötn 2004 eruption caused parts of Scandinavian airspace to be closed.  In fact, every Icelandic eruption of the 21st century has impacted aviation.

During the Eyjafjallajökull crisis, the aviation rules were relaxed and ash contamination was divided into different concentration zones (even though we can’t reliably map the difference between them).  In Europe, planes can now fly where up to 4000 micrograms of ash per cubic metre of atmosphere are predicted and this got things moving again in 2010 while the eruption was ongoing (yellow region on graph).  It is also a big reason why only 900 flights were cancelled during the 2011 Grímsvötn eruption, despite the fact that it erupted twice as much material in one tenth of the time.  With these new rules, it seems likely that only the largest eruptions could cause disruption on the the scale of Eyjafjallajökull.

Looking to the future

The chaos caused by the Eyjafjallajökull eruption was unprecedented because the global airline industry ‘took off’ and became part major of society during a lucky gap between powerful explosive eruptions in Iceland.  We can’t predict the next 70 years, but the following trends are likely:

• Iceland’s volcanoes will continue to erupt.  In particular, the time since that last eruptions of Hekla and Katla is longer than the average gap between their more recent eruptions.  Both volcanoes typically produce ash-rich eruptions.
• Global air traffic will continue to rise, making future airspace closures more and more expensive.
• The new flight rules will result in smaller areas being closed, and for shorter lengths of time, than during the ‘Avoid all ash’ era.  This will make continent-wide closures like Eyjafjallajökull caused much less likely.  Given the right weather conditions, however, it will still be possible for ash clouds to close airports in the busiest parts of NW Europe.