Hotspot volcanoes

Why are Indonesian volcanoes so dangerous? •

The Indonesian island chain was created by volcanism caused by one of the earth’s plates sliding under another. The Indonesian islands themselves are the peaks of volcanoes rising from the ocean.

The magma produced by volcanoes varies widely in composition, depending on the Earth’s mantle where the magma is produced. In Indonesia, the same process that creates volcanoes also creates terrible earthquakes and tsunamis. Along the southern archipelago of Indonesia, several catastrophic volcanic eruptions have also occurred.

To determine why Indonesian volcanoes are so deadly, a team of researchers led by Uppsala University looked at “primary” magma, which is produced deep in the earth’s mantle before being chemically transformed through interactions with the earth’s crust. Using a type of high-tech mass spectrometer, scientists examined crystals of pyroxene, one of the first crystals to form when magma cools.

Scientists have found very different patterns in the magmas of Bali and those of Java. In the Bali magma, the pyroxene crystals were very close to their original state, with the oxygen composition barely changed by travel through the earth’s crust.

Magma from Java interacted intensely with the Earth’s crust in comparison. Sometimes these interactions make the magma more explosive and more dangerous.

Java’s magma was collected from the Merapi volcano, which is one of Indonesia’s deadliest. This volcano has claimed nearly 2,000 lives over the past 100 years, with the last eruption killing 400 people.

“We could see that Merapi in Java had a very different isotopic signature from those of the Bali volcanoes. This is partly because Merapi’s magma interacts intensely with the earth’s crust before erupting,” explained study co-author Professor Valentin Troll.

“It’s very important because when the magma reacts with, for example, the limestone that’s in central Java right under the volcano, the magma becomes full to the bursting point with carbon dioxide and water, and eruptions become more explosive. Maybe that’s why Merapi is so dangerous.

Indonesia is a densely populated country, likely to become even more populated. The researchers hope their work is the foundation for a better understanding of the region’s volcanoes and similar volcanoes, so that lives and property can be saved in the future.

The study is published in the journal Nature Communication.

By Zach Fitzner, Personal editor