Friday, August 17, 2012

Two Shallow Quakes Hit Mammoth Mountain

Mammoth Mountain in California (located between Yosemite National Park, and Long Valley Caldera/Inyo Craters) is more commonly known locally as a ski/snowboarding resort, but few people actually realize it is a dormant, and potentially active volcano. Two shallow earthquakes, both less than 2km in depth, occurred near the summit of the restive giant. However, this does not indicate any impending eruption, although the quakes are likely tied to volcanic activity.

Map from USGS/CALVO detailing the locations of the most recent quakes at Mammoth.

Mammoth Mountain has not erupted in historical time. The last eruption was approximately 700 years ago, and occurred on the North side fo the mountain from vents that issued lava flows. The only other recorded activity since then, was a minor dike intrusion in 1989 that caused CO2 gas to be released at the SE foot of the mountain, killing a forest worker, and tree kill is apparent in the area to this day. The fact that the tress have not recovered, and CO2 gas is still present has prompted warning signs to be posted int he area since the incident, and the area remains off limits to people.

 Typically, there are a few quakes in the region yearly, but most of them are not near the summit as these two were, so it begs the question, is Mammoth Mountain slowly gearing up for a show?

An eruption at Mammoth Mountain might bode poorly for residents of California. Mammoth is a popular tourist attraction for skiers and snowboarders, is next to Yosemite National Park, and some evidence suggests a correlation between activity at Mammoth, and Long Valley Caldera (although Mammoth, even though it is situated on the NW rim of the Long Valley Caldera, is a chemically distinct magmatic system from Long Valley). An eruption today would likely be either phreatic (maar forming when ground water flashes to steam once it hits hot rock/magma), or an explosive cone forming eruption, much like its cinder cones to the south. However, Mammoth is a diverse volcano, having created lava domes, maars, and cinder cones, so any future activity could take many forms, however none are particularly life threatening if people are evacuated in advance of new activity.

The are has experienced a heightened level of seismicity (which includes Long Valley Caldera) since the mid-1970's. Causes of these quakes range from volcanic activity, to crustal adjustments (much like the recent quakes at Mauna Kea in Hawaii), or tectonic stress. In this case it is likely both a combination of crustal adjustment from the 1989 magma dike intrusion, and/or further injection of magma into the system are occurring. Magma dike intrusion does not always (and actually, not often at all) result in an eruption from a volcano. 90% of the time, the magma dike will cool slowly below ground, never breaching a seam or crack that would allow the lava to quickly decompress and erupt. So if this was actually dike intrusion, we might see more gas released like the 1989 event, or nothing at all.

CALVO is monitoring all volcanic systems in California and Nevada now, and have received new funding for furhter installation of scientific instruments on the most concerning volcanoes, including Mammoth Mountain. The project is not done yet, and monitoring on several of these volcanoes is done currently through the existing network. In the future, CALVO plans to install more detailed monitoring equipment that will measure gases, fumerole temperatures, harmonic tremor, and other factors that are currently unavailable for some volcanoes. 

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