SEATTLE – A lava formation inside Mount St. Helens' (search) crater has a new, glowing protrusion the size of a 30-story building.
The protrusion, which glows red at night, has risen by 330 feet in the past nine days, pushed up by magma (search), or molten rock, within the volcano, scientists said Friday.
"It seems like every time you think you know what's going on, (the volcano) twists and does something different," said Jeff Wynn, chief scientist for volcano hazards at the Cascades Volcano Observatory (search) in Vancouver.
The overall lava formation began building last month and has grown to roughly the size of an aircraft carrier, 900 feet long and 250 feet wide. Magma is reaching at the surface at the rate of 7 to 8 cubic meters -- about one large dump truck load -- every second, Wynn said.
"What we have been noticing with this monster is that it was growing at an unusually high rate and it was spreading out horizontally like a big pancake," Wynn said. "And now all of a sudden it's like a huge piston has been thrust up."
Like the old lava dome, formed in the six years after St. Helens' devastating May 18, 1980, eruption, the new formation is made of a type of volcanic rock called dacite, Wynn said. More than 63 percent silica, it tends to be sticky and viscous, unlike the free-flowing lava of Hawaii.
Temperatures on the new protrusion can spike as high as 1,200 degrees Fahrenheit.
The volcano rumbled back to life Sept. 23, with shuddering seismic activity that peaked above magnitude 3 as hot magma broke through rocks in its path. Molten rock first reached the surface Oct. 11, marking the resumption of dome-building activity that had stopped in 1986.
A more explosive eruption, possibly dropping ash within a 10-mile radius of the crater, is possible at any time, scientists have said.