SEATTLE - You can see them on the seismometers at the Pacific Northwest Seismic Network at the University of Washington. There are thousands of them - little squiggles that come every few minutes. Scientists call them ice quakes along with a few other names.
We think it's glacial noise coming from the bottom of a glacier. said Dr. Steve Malone, a UW professor emeritus and expert on the seismicity of volcanoes. Among other things, he tracked the buildup to the explosive eruption of Mount St. Helens in 1980.
But Malone does not think Mount Rainier is coming back to life because of where the quakes are, high on the mountain and on the surface of the rock, not deep down inside where signs of moving magma would be detected.
The signature on the seismometer is also different. Where volcanic earthquakes start with a sudden bang and then peter out, these start with a whimper, get bigger and then trail off.
There's another one every few minutes, but they are small, less than a magnitude1. In other words, they can't be felt.
They are also showing up on just three seismometers higher up on the mountain, one of them located near a popular stopping point for climbers known as Camp Muir.
They have been seen before. There were similar swarms in 1990 and 1998, but not this long. This latest wave began on May 21, faded away as June began and has picked up to a steady clip ever since.
It's interesting. It's one of these scientific curiosities, said Malone.
Wes Thelen with the Cascades Volcano Observatory in Vancouver, Wash. says there's been nothing unusual noted at the surface by park rangers. But the exact nature of what's going on between the mountain and its glaciers is still a mystery.
Glaciers move, but the last swarm of ice quakes like this occurred in 1998, 12 years ago. Thelen says the working theory is that water is moving between the glacier and the rock.
Scientists also don't believe the quakes had anything to do with a fatal avalanche last Saturday. They say these quakes are between the glacier and the rocks. The avalanche was at the surface during avalanche-prone conditions.