A slow-moving tongue of molten rock that recently broke off from the main flow of lava on the Big Island is inching its way closer to the boundary of Hawaii Volcanoes National Park and, not far from there, the Pacific Ocean.

The swath of lava is just west of the main flow that has for years run toward what is called the Waikupanaha ocean entry on the island's southeast side.

Jim Kauahikaua, scientist-in-charge of the U.S. Geological Survey's Hawaiian Volcano Observatory, said the new flow is likely to breach the national park boundary later this week.

“;It's not a terribly threatening flow,”; he said.

National Park Service officials are gearing up for the flow to cross onto federal land but are hesitant to predict when or whether it will crawl another mile to reach the ocean.

“;It's a dynamic and unpredictable phenomenon,”; said park ranger Mardie Lane, noting the flow also could stop and crust over or turn in another direction.

On Monday, Geological Survey volcanologists walked along the perimeter of the flow with hand-held global positioning system devices to measure its location. It had moved several hundred feet in three directions since the previous measurement 10 days before. The swath measured a mile or more across.

The public will not be prohibited from accessing park service land once the lava begins moving over the park boundary. But Lane stressed that to do so would be highly unwise.

For one, Chain of Craters Road ends about six miles from where the lava is expected to go, she said. Hikers would then have to traverse hot, humid, shadeless and rocky terrain that contains no public services.

They also might have to cope with vog - a mixture of sulfur dioxide and other volcanic gases that chemically interact with sunlight, oxygen, moisture and dust - and lava haze from molten rock striking sea water at the Waikupanaha ocean entry, she added.

One park ranger is now posted three days a week at the end of Chain of Craters Road, and more could be sent if the lava crosses the park border.

No lava has reached national park land since last year.

The land the flow is covering now as it approaches the park border is part of the mostly abandoned Royal Gardens subdivision. Last March, Hawaii County imposed a mandatory evacuation order there, mostly to control public access, said Hawaii County Civil Defense Administrator Quince Mento.

Only one resident continues to stay in the subdivision.