GIF: US Geological Survey

With 100-foot fire fountains sending rivers of lava toward the sea, it may seem like Kilauea has exhausted its pyrotechnic bag of tricks.

Turns out it hasn’t. Kilauea has now activated blue fire mode.

On Tuesday night, as lava continued to scorch soil and vegetation in the Leilani Estates Subdivision, scientists with the U.S. Geological Survey (USGS) Hawaii Volcano Observatory witnessed a strange and ethereal sight: bright blue flames emanating from cracks in the ground. They’re rather soothing to look at, like bioluminescent waves lapping against the shores of hell.

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But don’t let appearances fool you. This shit’s dangerous.

According to the USGS, the flames are the result of burning methane gas, a byproduct of all the vegetation currently smoldering beneath hot lava. Here’s how the agency described it in a Facebook post:

When hot lava buries plants and shrubs, methane gas is produced as a byproduct of burning vegetation. Methane gas can seep into subsurface voids and explode when heated, or as shown in this image, emerge from cracks in the ground several feet away. When ignited, the methane produces a blue flame.

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Concord University volcanologist Janine Krippner told Earther via Twitter direct message that a similar phenomenon has been witnessed at Indonesia’s Kawah Ijen volcano. There, sulfuric gases burning alongside lava have given past eruptions an electric blue glow.

Still, she said that to her knowledge, the phenomenon is “not common.”

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“There have also been methane explosions on the Kilauea lava flow over the past week where you can see little bursts of flame in some of the lava footage,” she continued.

The blue flames are the latest evidence of the incredible transformation playing out both on the surface and below ground as Kilauea’s lower East Rift Zone experiences its biggest eruption in decades.

As increasingly fresh magma spews forth from the Earth, it’s not only reshaping the landscape, but emitting plumes of sulfur dioxide that can produce dangerous volcanic smog. As lava reaches the ocean and interacts with seawater, it’s producing clouds of hydrochloric acid-rich “laze.” Meanwhile, the lava level at the summit crater continues to drop, sending towering plumes of volcanic ash thousands of feet into the air.

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No doubt Kilaueu’s got a few more incredible—and equally dangerous—surprises in store before this eruption dies down.