Scientists say a new tremor detected at Mount St. Helens in the northwestern United States is a sign the volcano is ready to erupt.
The tremor was detected early Sunday morning.
Geologists say there are signs that magma, or molten rock, is moving underground and building pressure inside the volcano.
The government has raised its alert level for Mount St. Helens and told people to leave the immediate area. Saturday, hundreds of visitors were evacuated from an observatory eight kilometers away.
But officials say residents of the nearest town, 48 kilometers to the west, are probably safe.
Scientists expect any new eruption to be much smaller than the 1980 Mount St. Helens explosion that killed 57 people and flattened thousands of hectares of forest.