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expert reaction to Bali’s Mount Agung volcano

Indonesian authorities have raised the state of alert to its highest level near Bali’s Mount Agung as officials fear a major eruption.


Dr Carmen Solana, Volcanologist, University of Portsmouth, said:

“A lot remains uncertain about what will happen.  We are still far from being able to forecast how eruptions are going to develop.  It could rapidly increase in activity and produce a vast eruption or it could die down.  Volcanic tremors are being registered, indicating that fluids (gas and magma) are moving under the ground.  So if it follows the most frequent trend, it is likely to continue increasing in explosivity – but at what rate and how large, nobody knows.

“The people affected were feeling very frustrated after the long lived crisis, but the volcano is proving the Indonesian volcanologists and emergency managers right in their decision to evacuate.  With volcanic eruptions, being on the cautious side is better than being overconfident.

“The volcanologists in the Indonesian Volcanic Survey have raised the alert to IV.  I will expect that, if the explosive activity increases further, they will expand the exclusion zone accordingly.

“Indonesian volcanoes erupt frequently and generally in an explosive or very explosive fashion.  In the past, eruptions have also produced Calderas, which are hollowed depressions several kilometres in size, left after vast explosive eruptions empty large reservoirs of magma and blast the rocks above.”


Prof. Bill McGuire, Emeritus Professor of Geophysical & Climate Hazards, UCL, said:

“While the situation is currently uncertain, Mount Agung has the potential for a major eruption that can impact upon the global climate as well as upon the local area.  The last eruption in 1963, scored a five on the Volcano Explosivity Index, putting it roughly on a par with the 1980 eruption of Mount St Helens (Washington State, USA).  That 1963 blast killed up to 1500 people on Bali, and also had an impact on the climate.  Agung’s eruptions seem to be very rich in sulphur, which has a significant cooling effect if it gets into the stratosphere.  The 1963 blast resulted in the formation of a veil of sulphuric acid particles in the stratosphere that spread across the planet, reducing global temperatures for several years.”


Dr Guy Gratton, Visiting Professor, Cranfield University, said:

“Authorities have closed Ngurah Rai airport on Bali ( because of a developing eruption of the nearby Agung volcano.  The reasons for this are the risk in the immediate vicinity of the airport of emissions from the volcano; the initial closure being for 24 hours and under review locally.  The risks to airport operations are of volcanic ash on the runway which can make landings and take-offs unpredictable, and of course all of the same risks to the buildings, people and surface transport that also affect the surrounding communities.

“The world has a network of Volcanic Ash Advisory Centres (VAAC) that monitor volcanic eruptions and provide the aviation industry with forecasts and observations of ash that can affect the safety of air transport.  Whilst northern Europe and Scandinavia are covered by the London VAAC (actually based at Met Office HQ in Exeter) Bali is covered by the Darwin VAAC in Australia, part of the Australian Bureau of Meteorology (  Darwin VAAC are issuing regular warnings now of the risk to volcanic ash between the surface and “Flight level 300” which is 9.1km above the surface.  Modern airliners typically are able to fly up to “Flight level 390” (11.9km) so in theory may be able to fly above this – but in practice this is usually considered unwise because of the risks associated with dealing with an unrelated in-flight emergency causing the aeroplane to have to descend.

“Volcanic ash predictions are obtained with a combination of satellite observations, surface measurements using an instrument called LIDAR (Laser Radar) and forecasts using computer models.  There are several problems with doing this accurately, which include that:

– It is very hard to safely measure what is coming out of a volcano;

– We know from observations during the 2010 Icelandic eruption especially that volcanic ash tends to form into relatively thin horizontal layers.  So the difference between the area of greatest risk, and least risk, may be a few hundred metres apart vertically;

– Around Bali at the moment, the local weather includes a lot of cloud.  This makes both surface and satellite observations very difficult.

“The main risk to aeroplanes of volcanic ash is to the engines.  A jet engine consists of three main parts – the air enters the compressor, then fuel is burned in that air in the combustion chamber and finally energy is taken out of that hot high velocity exhaust by the turbine.  Volcanic ash melts at temperatures below that normally found in the combustion chamber, but then the temperatures at the turbine blades (which are usually cooled) are generally below the melting point of the ash.  So the risk is particularly of ash solidifying onto the turbine blades, reducing the efficiency of the engine and potentially stopping it.

“In very severe ash encounters more extreme damage can occur, including to windows – the most famous experience of this was British Airways Flight 9 on 24 June 1982, which has been widely written about.

“Even whilst flying in volcanic ash, mostly it is not easy to see – the very high airflow rates through a jet engine mean that even very small concentrations can still damage the engine.  This is why forecast data and observations from satellites and LIDAR are very important to safety.

“Instruments are being developed to detect volcanic ash from aircraft, but these mostly either are unable to see ash within or through cloud, or require the aeroplane to be in the ash.  So it is likely that even if those were fitted and working, avoiding this airspace around Bali would still be essential for safety.  One such instrument is being developed by Nicarnica Aviation in Norway (, based upon the work of British Scientist Fred Prata.”


Prof. Mike Burton, Professor of Volcanology & Chair in Volcanology, University of Manchester, said:

On the main dangers if the volcano erupts:

“The main hazards are pyroclastic flows and lahars.  Pyroclastic flows have two main causes, firstly the collapse of lava accumulating in the summit area, which produces a hot rock avalanche, entraining cooler air and accelerating as it flows down the flanks of the volcano.  These flows can extend for several kilometres from the summit.  The second source of pyroclastic flows is eruption column collapse, when a volcanic explosion erupts a large volume of rock into the atmosphere, which then falls back down around the summit area, producing hot rock avalanches again, but this time with greater energy.

“Lahars are flows of mud and volcanic ash, which can be easily mobilised when freshly deposited ash is carried by the intense rains in the Indonesian rainy season.  The most intense rains usually occur between November to March, so an eruption in the coming weeks could lead to lahars quite quickly.  These mud flows are extremely hazardous as they can flow quickly and for long distances, scouring the land and damaging infrastructure, as well as posing a threat to life.

On whether there will be a lot of casualties like last time Agung erupted:

“The probability of a large number deaths and injuries is much lower now than it was in 1963, as modern volcano monitoring techniques have improved, there is much better awareness of the hazards posed by explosive eruptions and, most importantly, local populations are better informed, with clearer communication links.  Therefore, planning for a scenario similar to the 1963 eruption with pyroclastic flow run out up to 12 km from the summit is prudent, with a good probability that the actual eruption will be smaller than that.

On monitoring events and the role of social media:

“The current unrest on Agung may well lead to an eruption, and it will be closely monitored by the Indonesian authorities, who have already taken preventative action by evacuating local populations.  This unrest is being followed attentively by many people on Twitter and other internet sources, with continuous live updates, so any change in activity will be known worldwide within minutes.

On other dangers from an eruption beyond Bali and the local area:

“Apart from the local impact, an explosive eruption from Agung could affect air traffic through the dispersal of ash into the atmosphere, and climate, through the injection of Sulfur dioxide (SO2) and Hydrochloric acid (HCl) into the stratosphere.  The danger posed by ash to aircraft is that the ash melts within the jet engine, and then accumulates and solidifies on a cooler rotor, eventually blocking the engine entirely.”


Dr Matthew Watson, Reader in Natural Hazards, University of Bristol, said:

“Mount Agung in Indonesia has entered a magmatic phase of eruption after two months of heightened seismicity and steam-driven activity over the last week.  Over one hundred thousand people have been evacuated from what is now a 10 km exclusion zone, as the island prepares for a potential increase in intensity.

“Agung last erupted in 1963-4 and was a significant enough emitter to reduce global temperatures by 0.2-0.3 degrees for a year after the two main events in March and May 1963.

“From afar, the evacuation and planning seems very orderly and the authorities should be congratulated on managing a difficult situation well.  Whilst the last eruptive phase lasted for 11 months, it will be hard to predict both the size and longevity of the current eruption.  The island of Bali is already feeling some impact, due to loss of income from tourists, and the main airport in Denpasar has been closed as the aviation alert level rose to red.”


Prof. David Pyle, Professor in Earth Sciences, University of Oxford, said:

“Indonesia has the largest number of active volcanoes in the world, and considerable experience at monitoring and managing volcanic crises.  Report and photographs from Mount Agung show that it is now in a state of eruption, with explosions releasing clouds of volcanic ash a few kilometres above the top of the mountain.  At the moment, the main hazards from the eruption are volcanic mudflows – or lahars; and disruption to aviation from the ash.  The lahars form when the volcanic ash mixes with water (when it rains), and can run down the valleys around the mountain, rapidly and unexpectedly.

“Volcanic ash that is falling out of the eruption clouds is highly disruptive.  It is not likely to be toxic, but can cause irritation (to eyes), impede breathing, damage crops, upset grazing livestock, and make driving on paved roads hazardous.  Ash, even in small quantities, can be very hazardous to jet engines – and as the ash clouds drift away from the volcano, there will disruption to air traffic.  The ash clouds are closely monitored from the ground, and by satellite, and the local volcano observatory will keep aviation authorities up to date with regular notices.

“At the moment, the pattern of the eruption is similar to that during the last eruption, which began in February 1963.  The 1963 eruption reached a peak of activity after 1 – 3 months of ash emissions.  While there is no certainty that this eruption will follow the same pattern of behaviour as the last, it remains possible that the eruptive crisis could continue for some time.”


Prof. David Rothery, Professor of Planetary Geosciences, The Open University, said:

“The volcano Agung might at last be delivering the large eruption that has been feared for several weeks.  Ash is rising to a height of about 30 thousand feet, and dispersing east and south taking it over Bali’s international airport, which has had to be closed.  Airborne ash is a serious hazard to aircraft.

“The wisdom of the Indonesian authorities’ decision to evacuate residents from around the foot of the volcano will be apparent if there is substantial ashfall or, worse, a collapse of an eruption column resulting in fast-moving pyroclastic flows.  Airfall ash is a respiratory hazard, kills crops, and makes roofs collapse, and can turn into devastating mudflows (lahars) as soon as it rains.  Pyroclastic flows are hot and deadly.

“Most of the volcanoes in Indonesia, including Bali, are there because the ocean floor of the Indian-Australian tectonic plate is being pushed below (subducted) the plate carrying Indonesia.  This is the process that causes the earthquakes in the region.  Most of the magma that feeds the volcanoes is produced because the seawater that is carried down by the subducting plate escapes and lowers the melting temperature of the rock below the islands.  Molten rock, rich in steam and other gases, which is what we call magma, then rises upwards to feed the volcanoes.  If the gas escapes quietly, there is not much of a problem.  If it escapes violently, then we have an explosive eruption, which is what is feared in this case.

“Good sources of current information are and”


Declared interests

Dr Carmen Solana: “I have not got any interest to declare.”

Dr Guy Gratton: “Guy Gratton is an aeronautical engineer who also holds a Commercial Pilots Licence.  He was formerly head of the Facility for Airborne Atmospheric Measurements ( in which capacity he was mission scientist on board the Natural Environment Research Council’s ( former Dornier 228 “Airborne Research and Surveying Facility” aircraft when it made the first flights into the ash cloud over the UK from the Eyjafjallajökull volcano in April 2010.  Since December 2014 he has been Head of Airborne Science and Technology to the UK’s National Centre for Atmospheric Science ( and since January 2017 has been a Visiting Professor at Cranfield University (  Guy tweets at @GuyG_Boffin.  Guy Gratton is not a volcanologist.  High quality information on volcanology for journalists may be available from the press office at British Geological Survey: and universities who have geology departments.”

Dr Matthew Watson: “No conflicts.”

Prof. David Pyle: “Paid employment or self-employment – Professor of Earth Sciences in the University of Oxford.  Grant funding – funded by the Natural Environment Research Council (NERC), as part of the COMET and STREVA projects ( and  Voluntary appointments – none.  Memberships – American Geophysical Union.  Decision-making positions – none.  Other financial interest – none.”

Prof. David Rothery: “I run the OU’s Volcanoes, Earthquakes and Tsunamis course.  I am author of ‘Volcanoes, Earthquakes and Tsunamis: A complete introduction’.”

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