Predicting eruptions and dealing with Ash Rain

It can be difficult to live near active volcanoes, especially in countries like Japan, Indonesia and the Philippines.

A half billion people live in areas at high risk of volcanic eruptions. Indonesia is home to 129 volcanoes, or about 15.6% of the 829 worldwide.

It can be scary to wonder constantly when an eruption is going to start or stop. Recently, the Sinabung volcanic site in Sumatra, Indonesia has been spouting hot ash. Sinabung’s residents wonder every day when it will stop erupting.

It is difficult to predict the next volcanic eruption based on limited knowledge of past eruptions.

Anticipating volcanic eruptions

Vulcanologists have tried to predict eruptions using the “regularity pattern” of a volcano.

Volcanoes release volcanic material in a relatively constant volume over a period of time. The volume of material released by a volcano that occurs earlier than normal intervals will, in theory, be smaller than usual. It will produce more material if it occurs beyond the normal time interval.

Sinabung has not been active for 400 years, so it is difficult to predict its future. Deleng Sinabung is located in Karo Regency, North Sumatra, north of Toba caldera. The last time there was an eruption, which claimed 16 lives before the recent ones, was in the 1600s. People forget the dangers of the volcano after long periods of dormancy.

There are very few documents that describe the eruptions of Sinabung. This is due to its long dormancy. Before 2010, the eruptions were rare, and there was a long period between them. After 2010, they became more frequent.

Sinabung has erupted three times in the past: 2010, 2013 and 2014. This might indicate a real increase in the frequency of eruptions, which could mean that Sinabung is now experiencing a higher level of activity. However, this cannot be confirmed because earlier records are incomplete.

Due to the lack of data, it is also difficult to assign the Volcanic Expansivity Index ( VEI ) value of older eruptions. Also, we could not determine the exact volume ejected by older eruptions. There has been erosion in the area after 400 years.

Scientists who have been observing the mountain’s eruption column since 2010 report that the height of this column reaches between 1.5 and five kilometers with a volume of 10,000,000 cubic meters. Sinabung’s VEI is between 2 and 3, with one to three small eruptions per year. We can only hope that this is the regularity pattern of Sinabung.

Researchers with relative success have used this method. The average level of uncertainty is less than 20 percent. This method is particularly effective for volcanoes that have a VEI greater than 5. Researchers were able to accurately predict the eruptions of Pinatubo in the Philippines in 1991 and Ruapehu in New Zealand in 1996.

Ontake’s eruption in September caught Japan by surprise. EPA/Ministry of Land, Infrastructure, Transport, Tourism

We must remain vigilant. Sometimes, volcanoes can erupt without any prior warning. This is what happened in the recent Ontake eruption in Gifu.

Deadly spectacle

The cool climate, the clean water, and the beautiful views are all reasons why people in Indonesia want to live close to these sleeping giants.

The soil near volcanoes has a high fertility. We become less aware of disasters when the time between eruptions is long, up to 100 or more years.

Reconstruction of the Papandayan volcano eruption of 1722 on Java. Mirzam Abdurrahcman

Volcanoes can be deadly when they come to life. Volcanic ash is released. They are soft particles that have a diameter greater than 2mm. The volcanic ash will be launched into convective ascendance by a gas thrust, creating an explosion column. The hot ash will continue to rise until it reaches neutral buoyancy. This makes an umbrella of ash.

Rocks larger than 2mm in diameter are not usually able to climb. They shoot out like bombs.

It is an amazing spectacle, but it can be deadly within seconds. The loss of pressure will cause a pyroclastic stream to descend the slopes and destroy everything it touches. In this case, the area around the volcano must be evacuated.

Ash rain is a problem that people should be aware of. Later, the accumulation of these ashes will contribute to soil fertility. When floating in the atmosphere, however, it can cause lung irritation.