CBC] Mount St. Helens is rumbling again, but it's not the volcano that worries Washington state seismologists the most.
A 3.9-magnitude jolt Wednesday morning, about 11 km northeast of the
volcano, was the strongest tremor in the seismically active area since
1981. It was followed by a swarm of up to 150 smaller earthquakes.
In 1980, an eruption blew out the side of the volcano, killing 57
people and devastating the landscape. Cascades of water, mud, and rock
raged down valleys and knocked down forests.
But the latest quakes do not signal that the volcano is moving closer to another eruption, seismologist Seth Moran told On the Island host Gregor Craigie.
"There are earthquakes that are occurring at Mount St. Helens kind of
continuously," said Moran, who is a seismologist and
scientist-in-charge at the United States Geological Survey's Cascades
The most hazardous volcano in Washington state is considered by
seismologists to be Mount Rainier, where volcanic mud flows,
called lahars, roar down the Puyallup River drainage system every 500 to
"That's a long time from a humanity perspective, but from a geologic
perspective that's pretty frequent and a really good reason for
believing it's going to happen again," Moran said.
Tens of thousands of people are in the path of a large lahar,
including the Washington communities of Orting, Sumner and Puyallup. In
a worst-case scenario the lahar could reach Tacoma, though related
flooding is more likely to affect the city.
Moran said the lahar detection system set up two decades ago by
Pierce County with USGS assistance is now old technology, but it can be
updated to provide more effective and earlier warning for the "bump in
the night" event that could give residents as little as 45 minutes to
escape to safety.
"We've done studies of the volcano itself and there are parts of the
volcano, of the cone, that we know are somewhat unstable and have the
potential to let loose again with one of these things," Moran said. "The
likely scenario is it wouldn't happen unless the volcano is in a state
of unrest or eruption." Read More