This interview with volcanologist and geological disaster mitigation expert Devy Kamil Syahbana Phd of the Indonesian Centre of Vulcanology and Geological Hazard Mitigation was concluded barely minutes before last night’s eruption at 10:14 pm
RH Just recently the Indonesian Ministry of Energy and Mineral Resources issued a press release regarding an evaluation of Mt Agung’s acitivity between the 1stof May and the 7thof June 2018. Besides a report on the eruption of the 29thof May it was stated that seismic acitivity indicates there is still movement of magma from the depths to the surface. In the context of a major explosive eruption is this significant?
DKS: With the current level of Mt Agung’s activity, there is still the possibility of eruptions. But when you analyse the latest data, the probable explosivity is still low, and the potential danger zone is in a radius of 4km around the crater.The dangers include the ejection of incandescent rocks, and ash and sand falling. Ash fall will possibly be further than 4km, depending on the wind direction and speed. The potential for pyroclastic flows is currently fairly low.
RH: In the period between December 2017 til now as a whole the deformation trend of the mountain has been a continous deflation. But since the second week of May up until now you have indicated a reinflation based on GPS and tiltometer readings, and the data analysis indicates pressure from magma 3 to 4km below the crater. Do you have an idea of the volume? And in the current condition of Mt Agung does the volume of magma have to be as great as that of November 2017 (around 40 million m3) to result in an eruption the size of those of November 2017?
DKS: In order to trigger an eruption the size of that of November 2017, the volume of magma intrusion doesn’t have to be as big as that of September 2017 which reached 50 million m3. This is because in the crater there is already 23 million m3 of lava that could be ejected if the intrusion below the surface was large enough. However based on our GPS modeling , the current magma instrusion is around 1 million m3. We consider this volume to be too small to result in an eruption the size of that of November 2017. Let’s see how it develops further. Even the 1 million cubic meters could be released incrementally, not necessarily all at once.
RH: Is there a significant difference between the seismic activity recorded near the peak and that further down? And if so what does that indicate?
DKS: At the moment what we have is high frequency content (brittle failure caused by magma movement, mostly deep sourced) and also low frequency content (magmatic fluid movement in the forms of gas/liquid, mostly shallow sourced). Before, during September and October 2017 the main seismic activity was high frequency because the system was still closed, and it needed a lot breaking through as the magma forced its way through to the surface. Now the route is much clearer after the eruptions, so that’s why we are now seeing more low frequency quakes.
RH: Geochemical readings now are indicating there is still around 200 tons of SO2 gas being released daily from the crater, and there are indications that magma is still moving upwards to the crater. Besides eruptions, can these gases be fatal for climbers who, lulled by Agung’s seemingly calm condition, don’t heed the injunctions?
DKS: Of course the magmatic gases from Mt Agung are dangerous to our health. Those who survived thus far are just lucky. Mt Agung stands more than 3000m above sea level, and due to the high winds the gases are quickly dissipated. But imagine if the air is very humid, and it is clouded over – anyone at the peak could easily be contaminated by poison gas which could be fatal. There are among magmatic gases those such as CO2 which can’t be detected by smell or visually yet are fatal. If you suck in too much you’re going to die. Those illicit climbers are playing Russian Roulette – not only with the gases but even the possibility of an eruption when they are up there!
RH: In the ministry’s report it is said that the hotspots recorded by satelitte indicate that there is hot lava at the surface, though the rate of effusion to the surface is low. Clearly there are open channels for the magma to rise, though not overly large. If in the future there is a new intrusion of magma in large quantiites to the chambers below the crater will these channels be enough to release the pressure of the magmatic gases or will it eventually smash through the crust on the crater and result in an explosive eruption?
DKS: If there is enough energy, sure that is possible. There is a scenario that besides the crater already being full with lava, the ‘lava pancake’ would be smashed by [ressure from below. We don’t know when that could happen, but it would depend on there being enough pressure accumulated below the crater. For the time being the probability of that happening is low. But we expect small eruptions.
RH: Bearing in mind that the past cycles of Mt Agung have often been like long marathons, in your opinion is no longer possible to have a VEI (volcanic explosivity index) 5 eruption in the current cycle?
DKS: If we look at current data, it would be highly unlikely to have a VEI5 eruption. VEI 5 requires a lot of energy. But this cycle isn’t completely over, and the data could change, so we can’t really prophesy. But we are continually monitoring the data, and if something changes we will certainly report it.
RH: The primary source of magma for Agung and Batur are one and the same, though the channels and ‘chambers’ differ. In the past even Paon hill in Bebandem had a subsubidiary channel from Agung which made it erupt. Can you see a scenario in the current cycle in which Batur and Paon erupt as well?
DKS: The possibility of Paon erupting this time is very remote, Paon is a parasite cone which was formed as a result of major eruptions in the past. The magma channels have been depleted and are no longer active. As to Batur, it is possible that there could be an eruption but it wouldn’t be directly connected to Agung’s activity. However as their magmatic source is the same, the intrusion into Agung last year could have happened in Batur as well but to date our data does not show that. We measured the gas at Batur’s crater and the result shows negative.
RH: In your opinion what is the greatest obstacle in regards to disaster mitigation in the case of Mt Agung?
DKS: Lack of preparedness. Agung’s eruptions always leave a trail which show where the dangers lie – traces of pyroclastic flows, collapse, lava flows etc. All of that is found in the eruption disaster prone areas map of Gunung Agung (Peta Kawasan Rawan Bencana Erupsi Gunung Agung). Those areas marked red or yellow are areas which in the past experienced the primary result of Agung’s eruptions (incandescent rock, lava, pyroclastic flows etc) and secondary result (lahar flow). At the moment those areas are not clear of human settelement and activity. Bearing in mind the potential from Agung’s past eruptions, there will always be a risk of a disaster. If relocation is a difficult choice to put into effect, the only thing that can be done is to continually upgrade the preparedness of all parties. This in order that there will no longer difficulty in evacuation, no longer any panic or worse ignorance. This our collective duty, we need to pace ourselves in this maraton, be spartan, and continue to improve the capacity of the population around Mt Agung.
RH: Pak Devy thank you so much for your time and your answers!
photos ©Rio Helmi