Heavy rain caused volcano eruption in Indonesia, experts say

Indonesians are used to dealing with natural disasters. The country lies in the Circle of Fire, a strip around the Pacific Ocean that causes frequent earthquakes and volcanic activity.

But the eruption of Monte Semeru on the island of Java on Saturday (04) was different.

Days of heavy rain have gradually eroded Semeru’s lava dome, a hardened heap of lava that acts as a cover for the volcano, which has partially collapsed.

It was this “summit avalanche” that Indonesian volcano scholars believe caused the eruption, according to Eko Budi Lelono of Indonesia’s Ministry of Energy and Mineral Resources.

“Based on photos and data, we can compare the size of the dome before and after the December 4 eruption. We can see that a large part of the cap volume was lost after heavy rain that day,” he said.

A lava plug can be unstable and fall apart for various reasons, but there is a growing realization that heavy rain could be one of them.

The role of precipitation, in this case, raised questions about whether climate change could cause more frequent eruptions of this type.

This is a concern, because the outbreaks caused by the collapse of the lava lid tend to be stronger and more destructive than other types, scientists told the CNN.

Saturday’s explosion created what is known as a pyroclastic flow—fast-moving clouds of lava, gas, and ash.

The temperature of these clouds is typically between 800°C and 1,000 degrees Celsius, said Lelono.

Also, the flow can move fast — sometimes around 10 km/h, but up to 100 km/h — and it may be impossible to run.

More than 30 people died in the weekend’s eruption and authorities are looking for dozens of other missing people.

Thousands of buildings were damaged, many of them buried under heavy piles of ash that covered entire houses and villages. The force of this eruption was greater than normal.

Semeru hurled ash from about 15 kilometers high, when it normally only reaches a few meters, and the pyroclastic clouds reached more than 12 kilometers ashore, much further than the usual five kilometers, Eko said.

Millions of Indonesians live near the foot of volcanoes, where the soil is particularly fertile and good for cultivation. More than eight thousand live within 10 kilometers of Semeru.

Residents are sometimes warned that Semeru — one of Indonesia’s most active volcanoes — will erupt as its activity increases, but events triggered by rains like this are harder to predict, said Heather Handley, a volcanologist at Monash University in Australia , a CNN.

Advancing global warming is expected to make extreme rain events more common in many parts of the world, raising concerns that these larger eruptions could come with little or no warning.

Scientists don’t know if this will necessarily happen, but many of them have been asking this question since 2018, when Hawaii’s Kilauea volcano erupted after days of heavy rain.

“People have been thinking about the relationships between climate and triggers for volcanic eruptions,” Handley said.

“There’s still a lot we don’t know to explore, so it’s good to think about other external propulsion mechanisms from the volcanic eruption that we might otherwise have missed.”

Handley explained that there are several ways that increased rainfall and global warming could impact volcanic eruptions.

she pointed a study published in Nature on the Kilauea eruption, which suggests that days of heavy rain led to an increase in groundwater — which increased pressure, causing rocks to crack and slide.

When this happens, magma can more easily reach the Earth’s surface.

“If heavy rains are making it easier for lava to reach the surface, we could see an increase in the frequency of eruptions that we already have,” she said.

“There has also been a lot of thought about the effects of melting ice and snow, which usually occurs at the top of a volcano. When it melts, it takes pressure off the top — which can cause even more melting and consequently more frequent eruptions,” she said.

“But overall, we still don’t know much about the impacts of climate change on volcanic eruptions.”