05:30 PM PDT on Wednesday, May 17, 2006

By ANTONIA GIEDWOYN, kgw.com Staff

MOUNT ST. HELENS – The growing lava “spine” or “fin” on Mount St. Helens continues generating rockfall as it crumbles under its own weight.

Photos of the Mount St. Helens fin in changing stages.

On Saturday night, one of the larger earthquakes that typically occur once or twice per day was accompanied by a substantial amount of crumbling rock and ash clouds, according to the U.S. Geological Survey.

An image taken by a remote camera on the crater rim about 20 minutes after the event showed that “glowing hot rock debris had been delivered to the talus aprons that flank the steep north and south margins of the spine,” according to a USGS description.

A glow was also detected on satellite imagery monitored by other federal agencies.

Photographs taken by the agency over a recent 10-day period show crevices forming in the side of the fin and the top of the formation changing shape.

"The spine itself, as it rises, is growing at a rate of four or five feet a day... we're interested in knowing if it's coming up at a constant rate or if it's jerky -- we're still trying to get measurements to tell us that," said Dr. Thomas Pierson, a geologist with USGS.

Pierson said that even though Mount St. Helens is rebuilding at a "fairly slow" rate, if it continues at the current rate, in roughly 100 years it could build itself back up to what it looked like prior to 1980.

The growth of the new lava dome inside Mount St. Helens’ crater is characterized by minor ash production, low emissions of steam and volcanic gases and low-level earthquakes, according to USGS.

Eruptions could intensify suddenly or with little warning, triggering explosions and creating hazardous conditions within several miles of the crater and farther downwind, USGS reported Wednesday.

Thursday marks the 26th anniversary of Mount St. Helen's catastrophic May 18, 1980 eruption, which was the most deadly and economically destructive volcanic eruption in American history.

Fifty-seven people were killed and hundreds of homes, dozens of bridges and many miles of railways and highway were destroyed.

The eruption also dramatically altered the mountain's face.