(CNN)A small explosion from the Halemaumau crater in Hawaii's Kilauea volcano at about midnight local time created an ash cloud that reached up to 10,000 feet, according to an alert from the Hawaiian Volcano Observatory.
Kilauea explosion ash cloud reached up to 10,000 feet
More explosive events like the one on Friday could make for minor amounts of ashfall downwind at any time, and volcanic ash emissions remain high.
In addition, fast-moving lava crossed a road and threatened dozens of homes, prompting National Guard helicopters to airlift residents from Hawaii's lower Puna area.
Hawaii officials warned residents in affected areas to shelter in place Friday night and await further instructions. The lava forced the closure of Pohoiki Road, cutting off at least 40 homes, the Hawaii County Civil Defense said.
The agency urged residents near Highway 137 to be ready for voluntary evacuations should the threat grow.
"With fresher, hotter magma, there's the potential that the lava flows can move with greater ease and therefore cover more area," US Geological Survey geologist Janet Babb told CNN affiliate Hawaii News Now.
Resident Ikaika Marzo said the lava flow has left him and his neighbors rattled. It sounds like 10 or 20 jets taking off from your backyard at the same time, he told the affiliate.
"It's been like hell," he said. "It's like huge grenades going off. It shakes the whole community."
Volcanic gas emissions at the summit remain high and additional explosions are possible at any time, the observatory said.
The US Geological Survey also reported Saturday that a 5.0 magnitude earthquake occurred on Big Island on Saturday evening. The USGS said the epicenter was near Kilauea.
A few hours later, two active lava flows from fissures near Kilauea Volcano joined together into one flow near Highway 137, according to Hawaii County Civil Defense.
No structures are presently threatened, but at the current rate, the lava "may cross the highway within the next five to six hours," the agency said Saturday night.
Steve Gebbie lives in Leilani Estates, one of the hardest-hit areas. He said watching the lava destroy homes in his subdivision has been surreal.
When the Kilauea volcano erupted May 3, he joined hundreds of others forced from their homes in the subdivision. His home is still standing, but it's surrounded by toxic gas.
"It's hard to believe that it's happened in our neighborhood," said Gebbie, who's lived in the subdivision for 12 years. "And every day has gotten worse."
The lush green jungle has turned into rotten, yellow vegetation. Sections of streets that disappeared under the lava two weeks ago now look like a river of black molten rock.
Fissures, or cracks in the ground, are opening up, and a 23rd opened Saturday, the Hawaii Volcano Observatory said at a news conference. This newest fissure near the Kilauea Volcano is in the East Rift Zone.
The 22nd fissure was reported Friday, the observatory said. In a Saturday morning status report, the observatory said the rate of lava has increased between Friday and Saturday.
Fissure 17 is fountaining, the observatory said, and fissures 16 through 20 have merged, forming "a continuous line of spatter and fountaining." Some of the lava from fissure 20 was moving at a rate of about half a mile per hour toward the ocean Friday, observatory geologist Carolyn Parcheta said. Saturday afternoon, the observatory said the lava could cross Highway 137 in the next four to seven hours.
The lava flow from these fissures is very active and is advancing at rates up to 300 yards per hour, the observatory said. The flow from fissure 18 is moving more slowly, with fissure 17 moving even slower.
Lava has destroyed 40 structures so far, according to the Hawaii County Civil Defense.
On Thursday, an eruption from the volcano's summit shot ash and smoke 30,000 feet into the air. Authorities handed out almost 18,000 masks after Thursday's explosive eruption from the Kilauea summit.
The sulfur dioxide was thick afterward near the Hawaii Volcanoes National Park, enveloping the area in a dense fog that smelled of rotten eggs. In Pahoa, the earth sounded like it was cracking wide open as lava spattered and exploded from fissures.
US Geological Survey scientists said they expect the eruptions to continue.
"At any time, activity may again become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent," the agency said.