A substantial surge in sulfur dioxide gases being vented in the Halema'uma'u Crater at Hawaii Volcanoes National Park has prompted park officials to prepare an evacuation plan to protect locals and visitors from the potentially toxic gas.

For now, though, trade winds and rain seem to be safely dispersing the gases.

The new vent, located on Kilauea’s summit, appeared March 13 and immediately doubled the already elevated level of sulfur dioxide gas being emitted from the crater, according to park officials.

The rate at which SO2 is released by Kilauea volcano has typically been 150-200 tonnes/day, but in late December 2007, the emission rate increased to nearly 300 tonnes/day. This rate continued to rise into the new year, and by mid-February 2008, it fluctuated between 600 and 1000 tonnes/day, the U.S. Geological Survey reported. On March 12, the rate abruptly jumped to 1,500 tonnes/day. The following day, SO2 emission rates reached the highest recorded at Kilauea’s summit since measurements began in 1979—from 1,800 to 2,000 tonnes/day.

According to the Hawaiian Volcano Observatory, this increased venting and lava flows from the volcano present four hazardous conditions on Kilauea volcano: "Potentially harmful sulfur dioxide concentrations at the summit, potentially harmful sulfur dioxide concentrations and unstable conditions around the Pu`u `O`o/July 21/TEB vent area, lava flow threat to the Royal Gardens subdivision and the coastal plain to the southeast, and hazardous conditions associated with lava entering the ocean."

When SO2 levels doubled in December park officials moved to restrict access to roads and trails around Kilauea Caldera. In the wake of the latest venting, the park indefinitely closed Crater Rim Drive through the south caldera.

Karen Newton with the Park Service's Pacific West Regional Official said this afternoon that things are "kind of in a holding pattern right now" as trade winds and rains have kept the gases from drifting towards developed areas surrounding the park.

"They're still prepared, but they haven't issued an evacuation order yet," said the ranger.

Unlike other volcanoes elsewhere along the "ring of fire" that wraps much of the Pacific Ocean, Hawaiian volcanoes are not typically catastrophically explosive when they erupt, Ranger Newton said. The highlight more often involves lava flows, she said.

"If the summit should erupt, the SO2 levels would fall and then we'd have the greatest tourist destination in the world," said Ranger Newton.

The nearly 11-mile-long Crater Rim Drive wraps Kilauea and offers spectacular views of the volcano's caldera. It was on the rim of the caldera that Mark Twain watched a molten display of lava during an 1866 visit.

Officials say that while an eruption is a remote possibility, one is not currently expected.