US Geological Survey scientist Jim Kauahikaua said it was just the second time he'd ever seen blue flames during an eruption.
A third lava flow from Hawaii's erupting Kilauea volcano streamed into the ocean on Thursday as US Marine Corps helicopters stood by to evacuate a Big Island community should molten rock or huge cracks block its final escape route.
Low lava fountains were erupting from a almost continuous two-mile (3.22km) portion of the series of fissures that have opened up in the ground, scientists said.
Officials said Tuesday efforts to secure the wells from lava by quenching with water or plugging have likely mitigated any risk of an unabated release of hydrogen sulfide.
Residents down rift of the lava flows should be prepared to voluntarily evacuate at a moment's notice.
At least 22 lava fissures have opened in lower Puna, Hawaii, since a May 4 natural disaster near the Kilauea volcano.
The possibility of an air evacuation is emerging as a real possibility because scientists know that lava has been passing beneath Highway 130 along the East Rift Zone and surfacing in areas in and around Leilani Estates since the eruption began on May 3.
A lava fountain is observed from a helicopter flight over the Fissure 22 in Kilauea
Residents of Leilani Estates have been allowed to return at times since the eruptions began.
The plant has capacity to produce 38 megawatts of electricity, providing roughly one-quarter of the Big Island's daily energy demand.
Although the Kīlauea eruption did not itself cause any injuries, and mainly produced volcanic gas, its after-effects have been risky.
Kilauea's summit has seenexplosive eruptions since then, sending plumes of ash thousands of feet into the air.
Officials say almost 50 structures, including dozens of houses, have been destroyed since fissures began opening up in backyards on May 3.
A man hit by a "lava bomb" during eruptions says he's lucky to be alive.
No major injuries have been reported from lava haze. It can also cause explosions when it's ignited while trapped underground.
Clinton and some others had stayed behind, maintaining a vigil to protect the neighbourhood from a fissure that had opened up several hundred metres away.
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