In my senior year of high school, back before I really knew volcanoes would one day play a role in my professional life, Mount Pinatubo erupted in the Philippines. This explosive eruption came from a previously non-threatening and very eroded volcano that was covered in dense forests and, unfortunately, a whole lot of humans. 

While highly memorable, this massive eruption has nothing on the long-term danger posed by nearby Indonesian volcanoes. Merapi, on the island of Java, in particular, tends to explode more like a high school science project than the gentle oozing volcanoes we see in Hawaii and often in Iceland. 

Researchers looked at the chemical mix of tiny minerals formed in the lava to understand what exactly makes Merapi so explosive, and the answer is carbon dioxide gas. Accordion to Valentin Troll, a co-author of this study: Merapi’s magma interacts intensively with Earth’s crust before erupting. That’s highly important because when magma reacts with, for instance, the limestone that’s found in central Java right under the volcano, the magma becomes full to bursting point with carbon dioxide and water, and the eruptions get more explosive.

For those of you who may not have made fake volcanoes in school, the mix of vinegar and baking soda that is used produces carbon dioxide and water: exactly what is in this volcano! The thing is that in the volcano, the gases are mixed with molten rock instead of red food coloring. This horrible chemical reaction is thanks to that composition. 

There are place-to-place variations in the Earth’s mantle, where magma originates, and in the Earth’s crust, which the magma travels through. Beneath Java is the chemistry of explosive volcanism. Understanding what’s going on won’t bring back lives lost to Merapi, but hopefully, it will help us understand what future behavior to expect. This work appears in Nature Communications and was led by Frances Deegan.

More Information

Uppsala University press release

“Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis,” Frances M. Deegan et al., 2021 June 24, Nature Communications