The Hawaii Volcano Observatory says the explosion within Kilauea's Halemaumau crater produced a cloud that reached as high as 30,000 feet (9,000 meters) and was drifting downwind to the northeast.
A volcano on Hawaii's Big Island erupted anew Thursday with little sound and only modest fury, spewing a steely gray plume of ash about 9,100 metres (30,000 feet) into the sky that began raining down on a nearby town.
The explosion at the summit of Kilauea came shortly after 4 am following two weeks of volcanic activity that sent lava flows into neighbourhoods and destroyed at least 26 homes. Scientists said the eruption was the most powerful in recent days, though it probably lasted only a few minutes.
About every 10 minutes, the fissure shoots jets of steam and smoke 7 to 9 metres (20 to 30 feet) high, whining like a fighter jet.
Small fires burn in the distance as the lava flow's leading edge heads toward coastal Highway 137, one of the last exit routes for 2,000 residents to the south.
Toby Hazel, who lives in Pahoa, near the mountain, said she heard "a lot of booming sounds." Those came after days of earthquakes.
Sound sleepers
Some people in the community closest to the volcano slept through the blast, said Kanani Aton, a spokeswoman for Hawaii County Civil Defense, who spoke to relatives and friends in the town called Volcano.
At least one person who was awake heard nothing. Epic Lava tour operator John Tarson is an early riser and only learned about the eruption after receiving an alert on his phone. The plume, a towering column of ash reaching into a hazy sky, looked different than others he's witnessed, because of its sheer height.
"What I noticed is the plume was just rising straight into the air, and it was not tipping in any direction," he said. "We've been expecting this, and a lot of people are going to see it and get excited and scared."
Tour guide Scott Wiggers didn't hear the eruption either and wasn't aware anything happened. Later in the morning, he picked up four travellers for a tour and headed toward the volcano with the hopes of seeing "some action." But it was raining too hard for them to see much.
The only sign of the eruption he encountered was ash covering the back bumper of his truck.
Health risks
Residents as far away as Hilo, about 30 miles from Kilauea, were starting to notice the volcano's effects. Pua'ena Ahn, who lives in Hilo, complained about having laboured breathing, itchy, watery eyes and some skin irritation from airborne ash.
The National Weather Service issued an ash advisory and then extended it through early evening, and county officials distributed ash masks to area residents. Several schools closed because of the risk of elevated levels of sulfur dioxide, a volcanic gas.
The immediate risk health risk comes from ash particles in the air, said Dr Josh Green, a state senator who represents part of the Big Island.
Anyone with respiratory difficulties, such as asthma or emphysema, should limit exposure to the ash, Green said.
"People need to stay inside until the winds shift and the ash has settled," he said.
Extended exposure to sulfur dioxide can increase risk of bronchitis and upper respiratory infections in the long run, according to findings of a study Green worked on with other experts published in 2010 in the Journal of Toxicology and Environmental Health.
The Federal Aviation Administration extended a restriction on aircraft from entering the airspace up to 9,100 metres (30,000 feet) above Kilauea's summit. The earlier limit was up to 3,000 metres (10,000 feet). The prohibition applies to an 8-kilometre (5-mile) radius around the crater.
Thursday's eruption did not affect the Big Island's two largest airports in Hilo and in Kailua-Kona.
The crater spewing ash sits within Hawaii Volcanoes National Park, which has been closed since May 11 as a safety precaution over risks of a violent eruption.
Scientists warned May 9 that a drop in the lava lake at the summit might create conditions for a large explosion. Geologists predicted such a blast would mostly release trapped steam from flash-heated groundwater.
Kilauea, one of the world's most active volcanoes, has been erupting continuously since 1983. It's among the five volcanoes that form the Big Island, and it's the only one actively erupting. An eruption in 1924 killed one person and sent rocks, ash and dust into the air for 17 days.
Scientists cannot say why the eruption is happening now, given that Kilauea has been active for 35 years.
"There's so many variables. It's complicated, like a bad Facebook relationship status," said volcanologist Janine Krippner of Concord University in West Virginia. "Something will eventually change, like it has over and over and over again."
Robert Hughes owns the Aloha Junction Bed and Breakfast, about a mile and a half from the crater. He said he didn't hear anything and has yet to spot ash.
His business has been hit hard by fears of the volcano, a major attraction for visitors. He's lost hundreds of reservations and had just three guests Thursday instead of the 12 to 14 he typically serves.
"In the old days, people used to love to come see the volcano. They'd even take their little postcards, burn one corner in the lava flow, mail them off, stuff like that," he said. "Now they're acting like it's all super-dangerous and everything, but it just kind of oozes out."