HILO, Hawai'i — A small explosion that tossed some hot rocks more than 200 feet up onto the rim of Halema'uma'u crater added to the excitement at Kilauea volcano late Wednesday night.

Hawai'i Volcanoes National Park was closed at the time because of potentially hazardous fumes from Halema'uma'u, but the park reopened hours after the explosion.

The park was evacuated Tuesday and remained closed Wednesday because of the threat posed by sulfur dioxide emissions at the summit, but the trade winds have temporarily solved the problem by pushing volcanic emissions away from the visitors center and other busy parts of the park.

The winds also temporarily eliminated the emissions threat to residential areas around the park.

Scientists with the U.S. Geological Survey said the blast at the crater at 11:08 p.m. Wednesday apparently enlarged the new vent in the wall of the crater by about 15 to 30 feet, but that the explosion was considerably smaller than a similar blast on March 19.

Scientists found lava splatters and rocks that were ejected by the blast, including one block that was about 14 inches tall and 8 inches wide. Scientists said ash from the blast drifted on the wind about 19 miles to the Pahala area.

The explosion threw rock mostly toward the south, and the debris contained volcanic glass shards, according to a report by USGS scientists.

There is mounting evidence that a pool of molten lava is probably collecting 300 to 600 feet below the new vent, and scientists have been debating what trigger could cause that magma to rise to the surface in a crater eruption.

"We don't know for sure that it's there, but many of the signs that we see, the type of spatter that it's spitting out, the gases that are coming out, many of the signs suggest that magma is not too deep," said Hawaiian Volcano Observatory scientist-in-charge Jim Kauahikaua. "I can't tell you how shallow or how deep it is."

Scientists do not believe an eruption at Halema'uma'u is imminent because Kilauea has not been exhibiting swelling or an increase in earthquake activity, which are the usual clues that a summit eruption is coming.

Parks officials evacuated 2,000 people from the park on Tuesday, clearing facilities that included the 42-room Volcano House hotel and the Kilauea Military Camp, a vacation destination for military families. The evacuees were taken to hotels in Hilo. Kilauea Military Camp also was reopened yesterday.

Pu'u 'O'o on Kilauea's East Rift zone has been producing about 2,000 metric tons of sulfur dioxide a day for years, while only about 150 to 200 tons per day were being released at Halema'uma'u at the summit.

The new concerns about air quality began when sulfur dioxide emissions from the summit began to climb late last year, and by March 13 emissions from Halema'uma'u had climbed to record levels of 2,000 tons a day from a new vent that opened in the wall of the crater.

Emissions at the summit have since declined to about 800 metric tons, but the kona winds of earlier this week meant that even those levels of emissions posed a potential threat to park visitors and surrounding communities.

That threat eased when the trade winds resumed Wednesday afternoon, and the park reopened at 10 a.m. yesterday.