Tuesday, November 11, 2014

Quake Swarm South Of Lassen Volcanic Center

A nice quake swarm is occurring just South of Lassen Volcanic Center in California, US. The largest quake so far in the series has been a 3.9, and at this time the swarm is ongoing. So far around 35 quakes have occurred in the area over magnitude 1. It is unclear at this time whether the quakes are tectonic or volcanic in nature, however the fact that most are quite shallow could indicate this is merely a tectonic or hydrothermal event. Time will tell.


Quake swarm south of Lassen. Screenshot from Google Earth with USGS realtime quake overlay.

In all probability, as with many California quake swarms, this is related to fluid/hydrothermal movement within the crust, and probably isn't any big deal. The quakes to the East of the swarm seem to be at depths of up to 8km deep, and the ones to the West get progressively shallower. While this could indicate magma dike intrusion, that would be surprising, as some quakes are occurring on the surface, and so far there are no reports of activity in this very popular mountain hiking spot. It is likely, as most swarms in CA, that this will not result in an eruption, but it is still too early to know. 

Lassen last erupted in 1914-1917, California's only stratovolcano eruption in the last century. The eruption started with a phreatic explosion, and ended up building, and subsequently destroying, a summit lava dome which flung large boulders many miles from the summit. The famous 'Hot Rock' monument is a large boulder from this eruption. 

Lassen will likely erupt again in the future, although the current events are unlikely to make this happen. As with most West Coast volcanoes, their eruptions are infrequent, but very powerful. Should an eruption at Lassen occur in modern times, it would be more damaging than its previous eruption as the land around it has been developed.

So far, the news is slow to report, and they have less info than I do on my blog.

*****UPDATE 11/12/2014*****

The quake swarm continues. So far no quakes bigger than the 3.9. Most have been fairly near the 'middle' of the swarm area today, around depths of 4km. There has been no really detailed statement from USGS so far, other than 'swarms in this area are common' and 'this does not appear to be related to volcanic activity'. As I do not know where I could possibly view tremor plots in this area like you can with Alaskan, or Icelandic volcanoes, I can't really offer any more analysis than anyone else outside the USGS. If anything further actually develops, I'll update this post, but my guess is this is just another little swarm in the area, and not a whole lot will happen.

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