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Active flows: Here's how Indonesia's erupting volcano compares to Maunaloa

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Left to right: Mount Semeru emits a thick and ashy smoke from its center. Maunaloa shows a red and orange lava coming from a vent in the volcano.

Two volcanoes separated by more than 6,000 miles of ocean have recently erupted — but the similarities end there.

Mount Semeru is the highest mountain on the island of East Java in Indonesia. It erupted again on Sunday, expelling plumes of gas and ash.

The volcanic activity forced the evacuation of roughly 2,000 people and covered much of the area with a thick layer of ash.

Semeru is about 400 miles from the capital of Jakarta. Indonesia's Center for Volcanology and Geological Hazard Mitigation, or PVMBG, is asking people to stay at least 5 miles away from the volcano's center.

The status of the volcano was quickly moved to the highest alert level possible and shelters have been set up in the area for displaced families, according to the center.

Indonesia Volcano Eruption
This aerial photo taken with a drone shows houses covered in volcanic ashes following the eruption of Mount Semeru in Sumberwuluh village, Lumajang, East Java, Indonesia, Monday, Dec. 5, 2022.

While concerning, volcanos and earthquakes are not new to Indonesia.

"Last year, Mount Semeru's eruption resulted in 50 people died and almost 3,000 houses destroyed," said CARE Humanitarian and Emergency Response Manager Renee Manoppo in a press release Thursday.

She said that nonprofits such as CARE have shipped masks to the Indonesian Red Cross and are ready to deploy assistance when needed.

Here in Hawaiʻi, residents are also experiencing a reoccurring eruption — but why is Semeru more explosive than Maunaloa?

Geologist and University of Hawaiʻi professor Scott Rowland says it all comes down to the nature of the magma feeding the different volcanoes.

" Hawaiian magmas are hot, which makes them fluid," he said. "They can flow easily and they don't have a lot of gas in them. On the other hand, volcanoes such as Semeru, the magma is cool and viscous and has a lot of gas."

The gas pressure can build up to high values and eventually that gas pressure busts the lava into ash and ash particles, Rowland said.

Rowland adds that one of the greatest dangers of volcanoes like Mount Semeru are their extremely hot lava flows of more than 1,000 degrees Fahrenheit. That mix of gas, rocks and ash can move several hundred miles an hour.

Eruptive material such as rocks can also reach an estimated 5 miles from the summit, while the ash-sized material currently reaches 8 miles at Semeru, according to PVMBG.

"But it's a super explosive process and so when a volcano such as that erupts, it's best to just get away," Rowland said.

Savannah Harriman-Pote is the energy and climate change reporter.
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