Lava oozing from the Kilauea volcano since June has now invaded the Hawaiian village of Pahoa. With the molten rock threatening homes on the town's outskirts, some residents are packing up and evacuating. (See: "Hawaiian Volcano Sends Lava Oozing Toward Town.")
As of October 29, the lava had destroyed only a storage shed in the village. But the molten rock creeping forward five to ten yards (4.5 to 9 meters) every hour also stood less than a hundred yards (about 90 meters) from a nearby home. And a slower finger of lava that broke away from the main flow was no more than a hundred feet (30 meters) from another house.
If Kilauea continues to gush, the flow front, measuring less than 50 yards (15 meters) across, is expected to pass through a sparsely populated part of the town. "We're very fortunate, because the number and concentration of structures is very low in this area," says Darryl Oliveira, director of Hawaii County Civil Defense.
But Oliveira also cautions that the situation could change. In particular, "the flow front could widen," he says.
In fact, no one can predict whether the front will widen or when the flow will stop its march to the sea. It could continue gushing for days or weeks or longer. The eruption has proceeded in fits and starts since June, even pausing at times. (See: "Kilauea Volcano Pictures.")
Lava from Kilauea, a volcano that has been active since 1983, usually flows southward, down a slope and into the ocean. So it was startling this summer when a newly opened fissure in the Puu Oo crater started sending lava in the opposite direction, toward Pahoa. The flow traveled north, riding for some distance in a crack that kept the hot rock insulated, before passing through the uninhabited edge of the Kaohe Homesteads subdivision.
"It's sending flows in directions that haven't been threatened in a very long time," says Matthew Patrick, a geologist with the U.S. Geological Survey's Hawaiian Volcano Observatory, which overlooks the Kilauea caldera.
Using on-the-ground measurements and maps of the terrain created from satellite and plane observations, Patrick and his colleagues have been forecasting the movements of the lava. Over recent months their computer simulations have been generating continually updated maps showing probable routes of flow.
But even these predictions could be thrown off by an unnoticed crack that channels the lava or by a sudden surge of particularly runny flow.
For now, the big unknown is how much molten rock will ultimately emerge from the volcano's new fissure. Instruments can help scientists determine the rate of outflow at any given moment. But the discharge can speed up or slow down with little notice.
"The volcano in the past has repeatedly changed its mind," says Michael Garcia, a geologist at the University of Hawaii at Manoa. During a 1997 eruption, for example, underground lava tubes transporting molten rock seized up, stopping the flow.
Sudden subterranean swells provide at most only a few days' warning of an outburst. They are detected by measuring the tilt of the ground near the summit of the volcano, where the main magma chamber that feeds eruptions simmers beneath the ground.
With the full extent of the destruction impossible to predict, authorities must prepare for the worst case. Power lines are being moved. Forty to 50 homes are being evacuated, ones potentially threatened either by the lava itself or by clouds of noxious smoke it has released from incinerating tires and other refuse. Officials are contemplating closing a nearby school.
A serious worry is that the flow will block the region's main highway, currently about 800 yards from the front. Cutting a channel in the highway for the lava is an option, says Oliveira. In the meantime, construction crews have been rebuilding a two-lane road devastated years ago by another eruption, in order to provide an alternate route for the thousands of people who depend on the highway.
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