Mt. Fitzherbert

Before it let loose this week, Mount St. Helens started to hum.

Now geologists are trying to figure out whether the subtle tremor that preceded Tuesday's explosion might help them predict future outbursts.

They've already factored the tremor into their automated alarm system. If the volcano starts rattling again the way it did Tuesday, the computer will page scientists at the U.S. Geological Survey (USGS), day or night.

VANCOUVER, Wash. - Scientists are examining the crater of Mount St. Helens to see what happened in Tuesday's steam burst.

The U.S. Geological Survey's Jon Major told a news conference Thursday that there was no obvious new growth. The source of the eruption was found to be to the northwest of the lava dome, he said.