November 30, 2017

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.

Read more of this interview with Loÿc Vanderkluysen, PhD, at the Drexel News Blog.