SEATTLE – Mount St. Helens began rumbling more intensely Wednesday, prompting scientists to warn that a small or moderate eruption could happen in the next few days.

Earthquakes ranging from magnitude 2 to 2.5 were coming about four times a minute, possibly weakening the lava dome in the crater of the mountain, the U.S. Geological Survey said.

Scientists did not expect anything like the mountain’s devastating eruption in 1980, which killed 57 people and coated towns 250 miles away with ash. But a small or moderate blast could coat an area three miles around the volcano’s crater with ash and rock, scientists said.

Few people live near the mountain, which is surrounded by a national forest. The closest structure is the Johnston Ridge Observatory, about five miles from the crater.

The Geological Survey raised the mountain’s eruption advisory from Level 2 to Level 3 out of a possible 4 yesterday, prompting officials to begin notifying various state and federal agencies of a possible eruption. The USGS also has asked the National Weather Service to be ready to track an ash plume with its radar system.

In addition, scientists called off a plan to have two researchers study water rushing from the crater’s north face for signs of magma.

A plane was still able to fly over the crater yesterday to collect gas samples.