Geologists and disaster officials in the United States are waiting for the eruption of the Mount St Helens volcano near Seattle.
A mixture of volcanic gases and low-level earthquakes have raised fears that the mountain in Washington state might blow its top at any moment.
Some volcano experts had said an explosion would probably happen over the weekend. But as the time passed, others cautioned today that volcanic activity is difficult to predict.
"Right now, we're thinking it's about a 70 per cent chance that it will erupt and a 30 per cent chance that it just might go back to sleep," said US Geological Survey geologist Mr Tom Pierson today.
He said a buildup of earthquakes since a plume of steam was released on Friday indicate that pressure is still mounting within the volcano. Geological Survey crews also observed a shift in the crater floor and on part of the 1,000-foot lava dome that essentially serves as a plug for magma, he said.
"Cracks are opening up so we know something is pushing up close to the surface right now," Mr Pierson said.
Hundreds of people were cleared from a popular observatory close to the peak at the weekend following a tremor and brief release of steam. Most air traffic was prohibited within a five-mile radius of the volcano.
Scientists said they do not expect anything close to the devastation of Mount St Helen's May 18th, 1980, explosion, which killed 57 people and coated much of the Northwest with ash.
The mountain's alert was raised to Level 3, the highest possible, meaning an eruption is imminent. But scientists have discussed lowering their alert to indicate only that an eruption is possible.
AP