Mount Semeru on Java Island in Indonesia erupted suddenly on December 4th, 2021, after heavy rainfall caused the lava dome to collapse. Explosions from the slide sent gases and ash 40,000 feet into the air where it usually would be only hundreds. Heavy rains can make the eruption more powerful and increase the distance of pyroclastic flows. The explosion was caused by this external factor rather than by conditions inside the volcano.
Indonesia sits on top of the Ring of Fire, so the country experiences volcanic eruptions from 120 active volcanos. The risk to people adjacent to the mountain has only increased with population rise where prime agricultural land containing volcanic soil attracts more people. The mudflows on Java burned and killed dozens of people.
There is a growing interest in heavy rainfall due to global heating, where evaporation increases the amount of water vapor that is held in the atmosphere.
Heavy rain infiltrates volcanic systems, triggering eruptions that might not have occurred or been as severe. This particular eruption was not an isolated incident. On Hawaii’s big island, rare heavy rainfall caused the Kilauea to weaken rocks on the volcano's flanks sparking an eruption in 2018. Heavy rain caused the sides of the colossal mountain, which is the size of the island of Oahu, to generate sudden mudslides of lava, volcanic debris, and rain.
The dry volcanic ash absorbed the record rainfall increasing the weight on roofs of nearby homes.
Handley explained that there are several ways increased rain and global warming more generally could impact volcanic eruptions.
She pointed to a study published in Nature on the Kīlauea eruption, which suggested that days of heavy rain led to an increase in groundwater which increased underground pressure, causing rocks to crack and slip. had increased pressure in groundwater, which in turn caused rocks in the volcano to "fail," which basically means to crack or slip. When that happens, magma is able to more easily make its way to the Earth's surface."If heavy rainfall is making it easier for magma to get to the surface, we could see an increase in the frequency of eruptions that we get," she said."There's also been a lot of thought around the effects of melting ice and snow, which is often at the top of a volcano. When it melts, it takes the pressure off the top, which can cause even more melting, which can cause more frequent eruptions," she said."But overall, we don't have a very full understanding of the impacts of climate change on volcanic eruptions."
Indonesians warned that Mount Seberu is poised to erupt again soon.
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