Why Blue Flames Are Now Burning at Kilauea

Methane trapped underground is igniting blue flames near the volcano's lava flows. Experts say methane blasts are possible.

Footage: U.S. Geological Survey

Since it began erupting earlier this month, Kilauea has proven to be both dangerous and beautiful. Oozing red rivers of lava have slowly made their way across the region surrounding the volcano on Hawaii's Big Island, while fountains of molten rock dance and spatter around the erupting fissures.

Now, the volcano is producing a new spectacle—blue flames.

Video published yesterday by the U.S. Geological Survey shows streaks of eerie blue flames springing up between cracks in a road. The otherworldly effect is caused by methane, which is being produced as dead vegetation breaks down and the gas builds up in underground voids. When the methane seeps out and ignites, it produces the strange scene. (Learn the difference between lava and magma.)

The blue flames are only visible at night, so it's unclear how widespread they are and for how long they've been burning.

“They're not a common phenomenon,” says volcanologist Janine Krippner. “The only other place I know of it is in Indonesia.”

At the Kawah Ijen volcano in Indonesia, blue flames are a more common sight. There, the phenomenon is caused by sulfuric gases ignited by hot vents. Blue flames have also been documented at the Dallol volcano in Ethiopia, where they are created by sulfur dust in the region's soil. (Experts bust myths about Kilauea's hazards, from mega-tsunamis to chain reactions.)

The Kilauea eruption may be glowing blue in part because lava is entering developed areas where roads paved over the vegetation. Under normal conditions, plant breakdown produces methane that is gradually released into the air. Krippner thinks the paved roads could be acting as a sort of cap over the methane, causing it to build up in high concentrations. When it escapes through cracks in the inundated roads, it's suddenly exposed to heat and oxygen, and the gas ignites.

"The flames look so familiar because, despite the dramatic setting, it’s exactly like the flickers of blue in a campfire," says geologist Mika McKinnon.

Lava trapping vegetation in forested areas could produce methane blasts “capable of propelling boulder-sized rocks and other debris into the air,” according to a USGS Facebook post. “These explosions are unpredictable, and the only way to avoid them is to avoid the lava flows.”

"Those methane explosions are brief and localized, meaning the danger is only heightened if you’re already far too close to an active eruption," adds McKinnon.

Lava inundation and toxic gases carried in ash plumes are some of the most common volcanic dangers the islanders face. Officials in Hawaii are also watching for more explosive eruptions from Kilauea's summit crater, where steam buildup also has the potential to catapult large rocks at high speed.