A 44-acre chunk of the Big Island's Puna coast collapsed into the sea with high-energy pyrotechnics this week, exposing a 60-foot cliff face with a spurting, 6-foot-thick red geyser of molten rock.

The fountain, shooting out of a lava tube that was ripped open by the big collapse, is fast disappearing as the lava hardens around and under it and begins forming a new coastal rock bench.

"I'll be surprised if it lasts a week," said Jim Kauahikaua, head of the Hawaiian Volcano Observatory.

The collapse, about two miles from the end of Chain of Craters Road, began shortly before noon Tuesday and continued for several hours. When it stopped, a 34-acre rock bench and 10 acres of the adjacent cliff had tumbled into the sea, accompanied by explosions, flying gobs of molten rock, boulder missiles and clouds of rare volcanic products known as Pele's hair and limu o Pele.

It was the largest bench collapse since the current eruption of Kilauea started 22 years ago. The previous record occurred at the same spot in 1996, when 26 acres of bench and eight acres of sea cliff rolled into the ocean.

Benches occur as a continual flow of lava runs onto the shoreline, building a rock shelf that lies on an unstable bed of volcanic black sand and boulders. Kauahikaua said cracks started forming at the inland part of the bench several months ago and geologists began warning of an imminent collapse.

"We've been worried about this bench," said observatory geologist Christina Heliker.

"It's the highest hazard area along the coast," Kauahikaua said.

For several months, Hawai'i Volcanoes National Park has kept visitors well away from the danger zone. They are allowed to walk a half-mile from a parking area on a paved section of Chain of Craters Road, and then another third of a mile to a lookout two miles from the active flow, said Jim Gale, chief of interpretation for the park.

Even from that far away, the scene is spectacular, Gale said.

"The cliff just calved away like a glacier. It just sheared off that old wall. There's this gigantic steam plume and you can see the red just falling down, an incredible firehose display," he said.

The cliff resulting from the collapse is 60 feet high, and the lava tube is 15 feet below the cliff's lip, with the lava geyser erupting 45 feet above the level of the sea.

Heliker said the collapse occurred during onshore winds, and when geologists went to the edge of the cliff yesterday, they tallied all the volcanic products lying atop the cliff, either blown there by wind or by the force of explosion.

Gobs of splattered rock litter the first 170 feet from the edge of the cliff — material thrown up still molten that hardened after landing.

Boulders up to the size of a human head extend inward nearly 300 feet. These were hardened rocks that were blasted into the air and landed atop the cliff.

Rock dust, Pele's hair and limu o Pele extend inland 1,800 feet from the cliff's edge.

Pele's hair is thin strands of rock, formed when molten splatter is exploded upward and spun in hot air currents, so it is stretched like taffy until it hardens in fragile, hair-thin pieces that can be carried on the wind.

Limu o Pele forms when water enters an active lava tube. Steam instantly stretches the molten rock into a balloon, before the surface hardens and shatters, sending the thin sheets tumbling up into the air. The bits of limu o Pele are so thin you can sometimes see through them, and in the afternoon sun, they shine like gold on the surface of the land.

The collapse registered on seismographs on the Big Island, but did not cause a tsunami.

Kilauea Volcano has been erupting more or less continuously since Jan. 3, 1983, mostly from the Pu'u 'O'o vent on the volcano's east rift zone.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.