HILO, Hawai'i — Hundreds of small earthquakes that suggest magma is on the move under the surface of Kilauea Volcano sent scientists and national park officials scrambling yesterday, and prompted the rare closure of most of Hawai'i Volcanoes National Park.

Eleven campers and some livestock were evacuated from portions of the park as rangers monitored the unusual earthquake activity for signs of a shift in the ongoing Kilauea eruption.

Scientists said the tremors could be followed by a new surface breakout of lava.

Park Ranger Mardie Lane said it was the first time she could recall since about 1999 that seismic activity caused by underground magma movement prompted the park to take such extensive precautions.

Areas closed yesterday will remain closed until further notice, Lane said. Park officials will reassess the situation today.

The earthquake swarm began at 2:15 a.m. Over the next 17 hours, scientists recorded more than 250 earthquakes in Kilauea's upper east rift zone. Scientists said they know there were more earthquakes, but some were too small to locate.

Fresh cracks were reported in the Chain of Craters Road near the Mauna Ulu turnoff.

"It looks like the rift has expanded a bit, possibly to accommodate magma, and the earthquakes are accompanying that process," said Jim Kauahikaua, scientist-in-charge of the U.S. Geological Survey's Hawaiian Volcano Observatory.

Steve Brantley, deputy scientist-in-charge for the observatory, said the center of the earthquakes initially was about a mile southwest of Mauna Ulu, but during the day the hub of the seismic activity migrated about three miles down the east rift zone toward Pu'u 'O'o, the source of the ongoing eruption.

SAFETY FIRST

The earthquakes were centered one to two miles deep, and by 2 p.m. scientists reported most were occurring between the Pauahi and Makaopuhi craters.

At the same time, the summit area of Kilauea volcano began to deflate or contract, another clue that magma is shifting from beneath the summit to some other part of the volcano, Brantley said.

All of that activity raised concerns for the National Park Service, which closed the 18-mile Chain of Craters Road that park visitors normally use to reach lowland areas where lava flows into the sea.

Lane said upward of 1,000 people may drive at least partway down that road on a typical weekend day.

With the apparent new movement of magma, Lane said, the concern was that if lava suddenly burst to the surface in an unexpected area, it could cut roads and trails, spew out poisonous fumes or start brushfires that could pose a threat to visitors.

"It's a hidden hazard," Lane said. "Our job is to have this place open, but not at the risk of anybody's life."

Park officials also closed Hilina Pali Road, which extends toward the southern portions of the park, and closed much of Crater Rim Drive around the Kilauea caldera and summit area.

The campers were evacuated from a campground on Hilina Pali Road, and seven pack horses and mules were relocated to a safer pasture, Lane said.

Lane said this is the first time she could recall since about 1999 that seismic activity caused by underground magma movement prompted the park to take such extensive precautions.

She said the Kilauea Visitor Center, Jaggar Museum, Volcano House Hotel, Kilauea Military Camp and Volcano Art Center Gallery remained open.

BUT RISKS REMAIN

Brantley said that although the hub of the earthquake activity shifted downslope during the day yesterday, the Chain of Craters Road and other areas farther downslope from the earthquakes could still be at risk. "Assuming that our inference is correct (that the earthquakes signal magma movement), the magma could head to the surface at any time," he said.

Scientists say one possibility is that the flow of magma that normally supplies the ongoing Pu'u 'O'o eruption has been diverted at some point above the Pu'u 'O'o system.

A check by helicopter found that lava flows from Pu'u 'O'o toward the ocean appeared to be normal yesterday, but Brantley said scientists saw evidence the underground magma source that replenishes Pu'u 'O'o may have been choked off.

SEVERAL POSSIBILITIES

The floor of Pu'u 'O'o collapsed, rockfalls from the south wall of the Pu'u 'O'o cone also suggested instability there, and lava levels in what scientists call the East Pond vent nearby appeared to be dropping. Another vent on the south side of Pu'u 'O'o also collapsed.

All of that suggests that while lava continues to flow out of the magma reservoir at Pu'u 'O'o, it apparently isn't being replenished, causing the area to sink.

Scientist-in-charge Kauahikaua said the Hawaiian Volcano Observatory was watching the situation closely. There are several possible outcomes, he said.

"The most dramatic would be some sort of surface breakout of lava here near Mauna Ulu," Kauahikaua said. "The best would be, of course, that it's just going to remain underground, and it would be a very interesting Father's Day morning."

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.