Replies

It has been reported and noted by the USGS that an earthquake swarm has been occuring under Lake Yellowstone since December 26th.
The attached webicorder display shows that after the tremor swarm activtiy died down this evening a new pattern of potential classic harmonic tremors has started and continues at the time of this posting. Harmonic tremors could mean lava is now moving under the Yellowstone super volcano.
The USGS has made no updates since these tremors began.
Yellowstone webicorders can be accessed @ http://www.seis.utah.edu/helicorder/heli/yellowstone/index.html

Here’s a link to some information regarding Mt. Saint Helen’s about seismicity AFTER the main May 18, 1980 eruption. By the way, harmonics are the types of motion that cause buildings and bridges to fall apart.

http://vulcan.wr.usgs.gov/Volcanoes/MSH/Seismicity/seismic_studies_1980-1983.html

The following major types of seismograms have been recognized at Mount St. Helens:

1) deep earthquakes and those located away from the volcano, which produce high-frequency signatures and sharp arrivals similar to tectonic earthquakes,

2) shallow earthquakes, located under the dome at depths of less than 3 kilometers, which produce medium-to-low-frequency seismic arrivals,

3) surface events, such as gas and tephra events, rockfalls associated with dome growth, and snow and rock avalanches from the crater walls, which produce complicated signatures with no clear beginning or end, and

4) harmonic tremor, which is a long-lasting, very rhythmic signal whose origin is not well understood but which is often associated with active volcanoes.

Increased seismic activity also preceded the post-May 18 explosive eruptions of 1980. Each of the seismic precursors were of a slightly different character, but two categories were recognized: shallow volcanic earthquake precursors and harmonic tremor precursors. harmonic tremor is a nearly continuous train of vibrations lasting from a few minutes to several hours.

An increase in shallow earthquakes preceded the July and October 1980 eruptions when a lava dome was present in the crater. Harmonic tremor preceded the May 25, June 12, and August 7, 1980, eruptions when the vent was open and no dome existed. Having learned from the seismic buildup preceding the May 25 explosive eruption, seismologists were able to issue warnings of the subsequent explosive events by at least 2 hours.