Tuesday, September 25, 2012

Minor Quake Swarm At Lassen Volcanic National Park

A series of (up to now) 8 quakes has struck Lassen Peak, near Lake Helen at the South end of the mountain range. This is most likely tectonic, but the depths of all quakes were fairly consistent, consistent with a possible minor dike intrusion. USGS reports will likely indicate that this is normal background seismicity for the volcano, which has not had an eruption since 1914-1921.

The ongoing (I am at this point NOT going to call it a swarm, but it could become one if seismicity increases) activity at Lassen is at this time probably not volcanic as I stated earlier, however, the possibility does remain as this is one of the only Cascades range volcanoes aside from Mt Shasta, and Mt St Helens that have experienced any activity in the last century, or in historical (colonial) times. Cascade range volcanoes that have had eruptive activity in the last several centuries include Shasta, Hood, and Baker, but these volcanoes show very little seismicity that is of concern to anyone.

This is probably an event of crustal adjustment. However it is always wise to keep an eye on any Cascade range volcano and its quakes, as most of the range is situated near highly populated areas. An eruption from any Cascade range volcano can and does cause a lot of damage when they blow.

The last Cascade range volcano, after Lassen, to erupt was Mt St Helens in 1980.

3 comments:

  1. " as this is one of the only Cascades range volcanoes aside from Mt Shasta, and Mt St Helens that have experienced any activity in the last century"

    Mt. Shasta ? really ??

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  2. Yes, Mt. Shasta has indeed produced historical eruptions. According to the Smithsonian GVP:

    "Shasta's only historical eruption was observed from the ship of the explorer La Perouse off the California coast in 1786."

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  3. I should probably have added that Shasta erupted a bit earlier than "the past century". It does have the occasional landslide and seismic swarm. It is not a dead volcano.

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