Temblors signal slow change

•Seismologist says quakes originating in Government Camp

By Chad Garland / The Associated Press

SALEM — A swarm of little earthquakes has been rumbling this week beneath Mount Hood, Oregon’s tallest peak, but geologists say there’s no cause for alarm.

Sensors have recorded nearly 40 tremors near Government Camp, an unincorporated community in Clackamas County, since Sunday morning, with the largest being magnitude 2.3, barely big enough to feel.

The 11,240-foot mountain is a mecca for skiers, hikers and climbers. It is also volcanic. But researchers say the recent quakes are normal activity and aren’t signs of volcanic activity, such as magma heating up and starting to flow beneath the mountain.

“No one should start to batten down the hatches,” said Ian Madin, chief scientist with the Oregon Department of Geology and Mineral Industries.

Mount Hood is in a chain of volcanic peaks, called the Cascade Range, stretching from Canada into California. The chain includes Mount St. Helens, just to the north of Mount Hood, which erupted violently in 1980 and last erupted in January 2008.

Geologists say the recent quakes on Mount Hood appear to be caused by tectonic plates shifting, possibly along a nearby fault line deep in the earth, as the Cascades slowly stretch. It’s a process that has been happening over millions of years.

Seismologist Seth Moran at the Cascades Volcano Observatory in Vancouver, Wash., said it’s not clear where exactly the quakes originated — they are small and deep, and there are not enough seismic stations in the area to pinpoint them — but he thinks most occurred near Government Camp. He said “bursty” swarms of small earthquakes under the mountain’s south flank are normal, but a large quake right under its peak or a sustained series of quakes that build in magnitude could be cause for alarm.

The quakes this week fit within the broad category of what is normal in the region, Moran said. Little quakes like these give scientists a better understanding of what that “regular state of being” looks like, he said. They can then compare the “normal” against activity that may be a precursor of greater threats.

Geologists say the last confirmed eruption of Mount Hood was more than 230 years ago, and it’s hard to predict when it will blow again.

Any of the volcanoes in the Cascades could erupt again “in our lifetimes,” Moran said.