Agung Volcano, Bali - Eruption Update

Agung Volcano, Bali - Eruption Update

  • EOS News
28 Nov 2017
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Agung Volcano, as seen on 27 November 2017 (Source: Centre of Volcanology and Geological Hazard Mitigation)

Agung Volcano is currently erupting.

After over one month of intense seismic activity, during which the alert level at Agung was 4 (the highest), on 29 October 2017, at 4:00pm local time, the alert level was lowered to 3 (eruption imminent). This was due to a strong decrease in the number of earthquakes surrounding Agung, as well as a reduction in the seismic energy and amplitude of these quakes. 

On 21 November, a phreatic eruption occurred at 5:05pm, producing a plume that reached 700 metres (m) above the volcano’s summit. Ash drifted in an East-Southeast direction, up to a distance of more than 10 kilometres (km) from the summit. 

Thermal image of Agung, 21 November 2017 (Source: CVGHM)

Volcanic ash particles are very small fragments of magma or vent material that has been blown apart during an explosive volcanic eruption. These particles can be abrasive, conductive, and corrosive. 

In the days following 21 November, measurements indicated that sulphur dioxide – which was previously not detected – was degassing at 660 tonnes per day.

On 25 November, an eruption occurred at 5:30pm, producing a plume that reached 1500m above Agung’s summit. Ash drifted in a West-Southwest direction up to a distance of 12.5km from the summit. At midnight, incandescence was observed at the summit, signalling that the eruption was becoming magmatic in nature.

A RED-colour Volcano Observatory Notice for Aviation (VONA) was issued at 9:50pm, meaning that “eruption is underway or suspected with significant emission of volcanic ash into the atmosphere.”

A magmatic eruption began at 5:05am on 26 November, producing a dark-grey eruption column that reached 2000m above the summit. The plume drifted in an East-Southeast direction. 

5 millimetres (mm) of ash fall was observed in Sibetan village, and ash fell as far as Nusa Penida, Lombok, and Sumbawa. The intensity of the eruption increased at 5:45am, when the eruption column reached a height of 3000m above the summit, and then grew to 3300m by 11:00am.

A magmatic eruption began at 5:05am on 26 November, producing a dark-grey eruption column that reached 2000m above the summit (Source: CVGHM)

During the night of 26 November, two explosions from Agung were heard at the Rendang Observatory, located 12.5km away from the volcano’s summit. These explosions were followed by lightning.

At 6:00am on 27 November, Agung’s alert level was again raised to level 4 (the highest), based on a detailed evaluation that identified the unmistakable presence of magmatic components within the eruption products.

The community is advised to completely avoid the exclusion zone, which has been increased to include an 8km radius around the Agung crater, as well as areas that are within 10km of the crater in the North-Northwest and Southeast-South-Southwest directions.

The exclusion zone is dynamic and continuously being evaluated, meaning that it may change following developments and observations. According to the Centre of Volcanology and Geological Hazard Mitigation (CVGHM), Indonesia’s Geological Agency, the following villages are affected: Ban, Dukuh, Baturinggit, Sukadana, Kubu, Tulamben, Datah, Nawakerti, Pidpid, Buanagiri, Bebandem, Jungutan, Duda Utara, Amerta Buana, Sebudi, and Besakih dan Pempatan.

According to the CVGHM, Agung’s activity level is currently very high, and the probability of an even larger eruption is increasing. The intensity of such an eruption cannot be forecasted. It is particularly difficult to forecast the behaviour of Agung because of its small number of historical eruptions and the absence of geophysical monitoring data from these previous eruptions. 

A Volcanic Hazard Map of Agung Volcano (Source: CVGHM)

The only reference data available are from a sequence of earthquakes felt by the people around Agung in 1963, and again this year. Since the unrest began in mid-September, there has been a continuous increase in Agung’s volcanic activity.

The CVGHM has continuously and closely monitored all the changes in activity with a large variety of ground-based instruments and remote sensing techniques (e.g. seismicity, deformation, degassing, visual observations, and thermal data from CCTV, drones, and satellites.

According to the CVGHM and historical records, if an eruption similar to the one that occurred in 1963 were to occur, the hazards would range from volcanic bombs, to ash-fall, pyroclastic flows, lava flows, and lahars. An event similar to the one in 1963 (wherein the Volcanic Explosivity Index, VEI, was 5) could result in an eruption that would occur intermittently over several months.

In the event of such an eruption, the hazards most likely to occur within a radius of 8km of Agung would be pyroclastic falls, wherein clastic material measuring more than 6cm in diameter would be deposited.

The ash dispersal modelling conducted by CVGHM indicates that if an eruption with a VEI 3 were to occur, the most threatened areas would be those located West, Northwest, and North of Agung.

Ash is also expected to disrupt flight operations to and from Bali, Lombok, Surabaya and Banyuwangi. The potential for volcanic ash disruption in the air is, however, strongly influenced by wind direction and speed, so these outcomes will depend on the evolution of the situation.

 
 
 

References: 

Most of the information in this article was provided by the Centre of Volcanology and Geological Hazard Mitigation (CVGHM and MAGMA Indonesia).

Contributors: 

This piece was authored collaboratively by the Volcano Group at the Earth Observatory of Singapore.

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