Q&A: Could Bali’s Mount Agung Have a Major Eruption?

Ash plume over Mount Agung
Ash plume over Mount Agung
Mount Agung erupting in Bali, Indonesia, Nov. 27, 2017. Photo by Michael W. Ishak https://commons.wikimedia.org/wiki/Category:Mount_Agung#/media/File:Mount_Agung,_November_2017_eruption_-_27_Nov_2017_03.jpg

Around 100,000 people on the Indonesian island of Bali have been evacuated from their homes, and more could follow as the island’s most prominent mountain has begun to show signs of a potential major eruption.

Activity from Mount Agung began months ago with rumbling and a low-scale eruption started Nov. 25, resulting in ominous clouds of ash pouring from the volcano’s crater, but no catastrophic action.

Loÿc Vanderkluysen, PhD, assistant professor in Drexel’s College of Arts and Sciences, has been monitoring the situation from afar and conversing with his volcanologist colleagues about it. Here, he explains how the Indonesian Centre for Volcanology and Geological Hazard Mitigation (CVGHM) are preparing their residents and what the volcano could be building toward.

What causes a volcano like Mount Agung to suddenly become active like this?

Volcanic eruptions at the Earth’s surface are fed by reservoirs a few miles deep in the Earth’s crust, filled with hot, molten rock that we refer to as magma.

There are many ways these reservoirs can be stirred to activity; commonly, it happens because of the slow accumulation of gases building up pressure like a pressure cooker, or with the injection of fresh, new magma from even greater depths. In the case of Agung, it had a violent eruption in 1963 that caused more than a thousand fatalities, so the volcano was never inactive – just dormant. It’s not unusual for volcanoes to wake from dormancy after several decades of slumber. Mount St. Helens had a major eruption in 1980, but returned to activity in 2004 after about two decades of quiescence.

What is the likelihood that this volcano will have a major eruption — like in 1963?

The Indonesian Centre for Volcanology and Geological Hazard Mitigation (CVGHM) has been doing a fantastic job of managing the crisis so far, and raised the alert level to its maximum level of IV on Monday. Based on the continued increase in activity and what is being observed in seismic and gas measurements, CVGHM volcanologists consider the probability of a larger eruption is fairly high.

What would that look like?

Local authorities expect a major eruption to look like the one from 1963; a column of ash might rise to heights of 10 or 15 miles above the volcano, raining volcanic ash on most of the island of Bali, and sending clouds of hot ash and mud flows barreling down the flanks of the mountain.

How quickly could an eruption like that develop after the first warning signs?

Some volcanoes give hardly any warning at all prior to eruption, but it generally takes days to weeks. The first increase in seismic activity was detected at Agung in August, and the alert level was raised to II in September. The area has been under elevated alert level (III or IV) for the last 10 weeks.

People forget that the first small eruptions at Mount St. Helens occurred 7 weeks prior to its major eruption in May 1980.

If a major eruption occurred, would people on Bali be in danger?

Even the smaller eruptions that we have observed in the last few days can present serious hazards. The exclusion zone has now been extended to a radius of 8 km (5 miles) of the summit crater, and evacuations are ongoing. Within that zone, people are at risk of being pelted by falling rocks or hit by the fast-moving clouds of hot gases and volcanic ash we call pyroclastic flows. No one should approach the volcano at any cost.

One of the major source of fatalities of the 1963 eruption were lahars — an Indonesian term used to describe volcanic mud flows — which are caused by the accumulation of volcanic particles in streams and lakes. For that reason, among others, the hazard zone around Agung includes river valleys within 12 km (7.5 miles) of the volcano, though I’ve now heard it may actually be 15 km (over 9 miles).

People should be aware of the risks associated with volcano-triggered flash floods, particularlly during the current period of relatively high rainfall. Lahars have already been observed in the last couple of days.

Beside pyroclastic fall and lahars — the most direct hazards that are expected to be limited to within the boundaries of the exclusion zones, all Balinese are faced with exposure to volcanic ash fall.

Volcanic ash is composed of very small fragments of rock and volcanic glass (about 100 microns, or 1/250th of an inch), which can irritate the eyes and lungs if inhaled. During periods of ash fall, people should limit their exposure by wearing a mask to prevent inhalation.

Beyond staying out of the exclusion areas, what else do you think people in Bali should know?

I recommend that Bali residents and visitors familiarize themselves with the hazards of volcanic ash— such as reading this pamphlet from the International Volcanic Health Hazard Network (IVHHN).

Visitors planning a visit to Bali should buy masks prior to their trip, and bring extra along with them in case of shortage in Bali. The IVHHN note that certified masks with a N95 rating, adjusted to fit snugly to the face, are effective at filtering ash.

Lastly, conditions during volcanic crises can change rapidly, and anyone in Bali or planning a visit should stay updated by following the updates and instructions from the authorities on the ground, the CVGHM.

Media interested in speaking to Vanderkluysen should contact Frank Otto at 215.571.4244 or fmo26@drexel.edu.

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