Kilauea's falling lava lake has likely descended to a level at or below the water table, allowing water to run on to the top of its lava column and create steam-driven blasts, they said.
Kilauea, a massive shield volcano on Hawaii's Big Island, is the place of the world's longest ongoing eruption, one that has oozed lava since 1983.
But they say they expect no loss of life given that the most exposed residential areas have been evacuated and the region where the volcano is located - on the southeastern part of the island - is not densely populated.
"The resulting ash plume will cover the surrounding area".
The experts of the US Geological Survey issued a red danger code, which means that there is an ash cloud in the air.
But clearly, not everyone was so anxious.
In the village of Volcano, barely three miles from the summit, lifelong resident Lance Benevides went through the familiar protocol to cope with an eruption, including detaching his roof gutters from his water tank to keep ash out of the catchment system that serves as his water supply. "It's a trickle-down effect that affects everybody", she said.
The USGS said, Depending on weather conditions, that the ash might fall as far as Hilo, 30 miles to the northeast.
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Eruptions at Kilauea have opened at least 20 fissures since activity began two weeks ago.
A change in wind direction caused gas spewing from fissures to drift northwest towards Pahoa, prompting National guard troops to don gas masks at a nearby road intersection, according to a Reuters reporter.
"Protect yourself from ash fallout", the officials warned in an alert. Due to elevated sulfur dioxide levels in the area, local schools are also closed, Hawaii County Civil Defense said.
The volcano.it's a real dynamic situation up there. we could have additional events like this morning that punch up and then die back down really quickly. we could have more sustained ash.
Time lapse images taken from a camera at the Gemini Telescope on the Big Island captured the eruption plume just before sunrise.
That rock was hurled from the volcano's Overlook crater and landed in an ash-covered parking lot.
Two astronauts also reported being able to see an ash plume from the volcano from space earlier this week.
"So a big event that got people's attention but not with widespread impacts", Michelle Coombes said.