Mt. St. Helens Filling With Lava, Shaking With Continual Quakes
For more than a year, Mt. St. Helens has been oozing lava into its crater at the rate of about 10 cubic yards -- a large dump truck load -- every three seconds. With the sticky molten rock comes a drumfire of small earthquakes.
The movement of lava up through the volcano is “like a sticky piston trying to rise in a rusty cylinder,” U.S. Geological Survey geologist Dave Sherrod said this week at the agency’s Cascades Volcano Observatory in Vancouver, Wash. “These quakes are very small -- we think they’re associated with that sticking and slipping as the ground is deformed and relaxes.”
Mt. St. Helens’ violent eruption on May 18, 1980, blasted 3.7 billion cubic yards of ash and debris off the top of the mountain and reduced its peak from 9,677 feet to 8,325 feet. Fifty-seven people died in the blast, which left a gaping crater in place of the perfect, snow-clad cone about 100 miles south of Seattle.
Mt. St. Helens rumbled for another six years, extruding 97 million cubic yards of lava onto the crater floor in a series of 22 eruptions that built an 876-foot dome. The volcano fell silent in 1986.
Then in September 2004, the low-level quakes began -- occasionally spiking above magnitude 3, but generally ranging between magnitude 1 and 2. In the last 15 months, the mountain has squeezed out about 102 million cubic yards of lava.
Weather conditions have prevented aerial observation of the crater since Oct. 24, but geologists have relied on a network of remote monitoring equipment to tell them what’s happening.