Mt. Fitzherbert

Scientists believe Mount St. Helens will erupt today, the 26th anniversary of the explosive eruption that produced the world's largest known landslide, killed 57 people and launched a new era in volcanology.

"It's been erupting almost continuously since late 2004," said Tom Pierson, a U.S. Geological Survey researcher at the Cascades Volcano Observatory in Vancouver. So it's a good bet it will also erupt today, Pierson said.

The real question that's "driving everyone nuts" in the volcano-watching research community, he said, is what's causing this period of eruption -- and if its peculiarities indicate the mountain is building pressure for another explosive event.

Unlike the massive, catastrophic blast of 1980, the current eruption on St. Helens is slowly, steadily pushing up a relatively cool and solid column of lava rock, or magma.