EXPERT COMMENT: Agung Volcano Q&A with the University's Chair in Volcanology
No one knows if this will happen in the next few days, but it easily could, and sooner or later there will be a further eruption.
Professor Mike Burton, Chair in Volcanology at The University of Manchester, takes part in expert Q&A dicussing what is causing the latest seismic activity at the Agung Volcano and the threat it poses to the local population. When it last erupted in 1963 it killed more than 1500 people.
What is causing this current activity?
The most likely cause of this latest unrest is the injection of hot, fluid magma called basalt into a cooler more viscous magma called andesite. When the basalt cools it releases gases, which are now being observed at the summit, and leads to a pressurisation of the magma chamber, resulting is seismicity. Whether this leads to eruption or not depends on whether the pressure in the magma chamber can exceed the confining pressure, and produce a magma ascent to the surface in the form of an eruption.
When will Agung erupt, is it imminent?
No one knows if this will happen in the next few days, but it easily could, and sooner or later there will be a further eruption. The decision by the Indonesian authorities to evacuate was sensible, and it appears that the local populations have been well informed on the dangers posed by Agung.
What are the biggest dangers to the local population?
The main hazards are pyroclastic flows and lahars.
Pyroclastic flows have two main causes, 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 km 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.
Is there likely to be a many casualties?
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.
What are the other dangers of such an eruption?
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. The injection of SO2 high into the atmosphere can produce climatic impacts through the generation of sulphuric acid aerosol droplets which reflect solar radiation, cooling the planet. Stratospheric injection of HCl can produce ozone depletion, but the humid conditions of Indonesia means that the bulk of erupted HCl will be rained out.
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 life updates, so any change in activity will be known worldwide within minutes. In case of eruption, the volcanology group at the University of Manchester will produce calculations of the emission rate of SO2 from Agung using satellite data, in order to track the evolution of the eruption.