The volcano began rumbling last week, and by Wednesday earthquakes ranging from magnitude 2 to 2.8 were coming about four times a minute, possibly weakening the lava dome in the crater of the 8,364-foot mountain, the U.S. Geological Survey said. (Related graphic: More on Mount St. Helens)
The quakes continued to strengthen early Thursday with several exceeding magnitude 3, according to the Web site of the Pacific Northwest Seismograph Network.
