Wednesday, February 12, 2014

Quake Swarm And Possible Dike Intrusion At Mammoth [UPDATED 2/19/2014]

Mammoth Mountain is experiencing heightened quake activity directly below the main summit, at depths of around 5km, which could indicate magma dike intrusion into the mountain. Over ten quakes have occurred (over mag 1.0, there are many below this number) under the summit area, close to the area of the previous suspected intrusion that resulted in the release of a large amount of CO2 gas, which destroyed a portion of the forest, and ended up killing a park ranger.

The current level of unrest at Mammoth is not typical.


Image from Google earth with USGS real-time quake overlay of Mammoth Mountain, CA

Mammoth Mountain has not had any recent eruptions (the last was about 700 years ago), however it can still be deadly, as numerous gas and volcanic landscape incidents have proven. As recently as April, 2006, several people were killed after falling into a gas filled volcanic chasm, and as mentioned earlier, previous dike intrusions have caught people unaware. Tree kill accompanied the last magma intrusion, a visible reminder that this volcano, while generally quiet, is still very much alive, and will erupt in the future.


Image from USGS website showing the tree kill by 1989's magma dike intrusion. 

Mammoth mountain is a popular resort and skiing town in central California. It borders both the famous National park of Yosemite, and California's very own super-volcano, the Long Valley Caldera. Mammoth Mountain lies on the westernmost rim of the Long Valley caldera, but volcanologists assert that it is a separate volcanic system, and very chemically distinct from Long Valley tuffs. Other volcanic systems nearby that bisect the Long Valley/Mammoth area are the Inyo craters to the ENE, and Mono Lake to the North.

It is not likely that a magma intrusion would trigger an eruption at this stage. The intrusion and seismicity appears to be quite weak in nature, however this could be a precursor to heightened emissions of CO2 on the volcano, which can pose health and death risks to anyone or anything that gets trapped in a pocket of gas for any length of time.

If an eruption were to occur today, it would likely be a repeat of its recent eruptions, meaning phreatic explosions, when melt water comes into contact with hot rocks, flashing into steam and creating an explosion. It is unlikely that an eruption would be magmatic at this stage, but anything is possible with volcanoes. I'll be keeping my eye on this one... and staying off the slopes for a while!

*****UPDATE*****

The quake swarm CONTINUES today, adding three 2.7 magnitude quakes, a 2.2 quake, and about 15 or more <2.0 quakes. Some of the depths are getting shallower (in the 4km range), indicating that magma might indeed be rising. If this is the case, I would probably start thinking about raising the alert level to 'Yellow', as a precaution, due to the fact that this is a very popular mountain, and lives could be at risk if this continues. At this time, I would be strongly in favor of the conclusion that this is a magma intrusion, with possible eruptive potential.


Updated screenshot of Mammoth Mountain with USGS real-time overlay depicting 2.2-2.7 magnitude quakes (the larger dots). 

Keep an eye on Mammoth Mountain, as this has not occurred since the 1989 dike intrusion incident, and is not typical of the volcano.


*****UPDATE*****

One quake which USGS earlier identified as a magnitude 2.7, slight SE of the summit, was upgraded to a 3.0.

*****UPDATE 2/6/2014*****
No new surprises this morning. About ten or so small quakes (less than 2.0) have occurred, probably aftershocks of the main event, a 3.0. The other quakes which registered 2.7, 2.7, and 2.2 are no longer appearing on USGS records, as they may have been corrected/erased. The 3.0 quake still stands as the 'main event', however larger quakes are still possible. The next few days will likely determine whether or not the swarm is over.

It is possible that this dike intrusion event can increase degassing at Mammoth. Visitors should exercise caution, and consult park rangers before hiking/skiing/snowboarding on the mountain, and obey any caution signs that indicate a high level of CO2. Those that have been there before are familiar with some of the roped off 'craters' that tend to let out a large amount of gas.

At this time, there are only a couple of risks, none of which are new per se, but they could be a bit more severe. CO2 displaces oxygen, which causes suffocation. Any further quakes, especially larger ones, can trigger landslides or avalanches, however due to the drought, the snowfall on Mammoth is likely man-made and not very thick, so this risk is probably a bit lower than it would be on a 'normal year' for California (in regards to rainfall/snow pack).

If any further activity takes place, I will update this post.

*****UPDATE*****

A 2.0 mag quake struck at 4.5km depth (rising). Could be the swarm is still ongoing. 




The current swarm with mag <1 quakes included.

*****UPDATE 2/8/2014*****

The quake swarm continues, with several mag 2.0 or greater quakes occurring within the last 24 hours, and many smaller quakes. The depths are ranging from around 5km, to less than 1km in depth, suggesting either crust adjusting to new magma, or rising magma and rock fracture. The intrusion does not appear to be over at this time. The lighter plots in the below image denote shallower depths, as the darker ones are deeper. Note that the shallower quakes are around the base of the volcano.




This graph from the Mammoth Mountain observatory shows increased uplift (bottom graph, far right) during the current seismic episode. Note that in 2006, when the last gas fatalities occurred, show significant deflation followed by inflation.



Chart displaying the time/depth/magnitude of the quakes.


*****UPDATE*****

A 2.3 mag quake struck at 2:32 UTC on the SE flank of the mountain, at a preliminary depth of 5km.


Google Earth with USGS overlay displaying position of quakes to date since onset of swarm.

*****UPDATE 2/10/2014*****

The quake swarm continues with a mag 2.5 and several smaller quakes within the last hour or so (image below)


*****UPDATE 2/11/2014*****

The situation is pretty much the same. More mag 2.5 quakes, and lots of little ones. If anything significant changes, I will update this post.

*****UPDATE*****
An eruption is not imminent. This has never been stated. This quake swarm is not typical of this mountain, and is related to dike intrusion. That being said, the eruption risk should be elevated, due to the fact that historical intrusions have taken place since 1989, and 2006 (and probably earlier). Magma chambers can remain pressurized for a very long time, and can be triggered for eruption by a very diverse set of circumstances. Every intrusion increases magma pressure beneath the mountain, which can include effects such as increased gas emission, instability in rock faces, and of course the risk of an eruption. None of this is imminent, but it is possible. Some sites are saying that this is a very minor and insignificant event. I do not agree. I believe this event compounds on top of others which have passed, and is every bit as risky as any other volcano which is experiencing unrest. Time will tell whether or not this alters conditions on the volcano. In regards to personal risk,  it is absolutely up to the visitor to the area to decide the pros and cons of visiting this volcano. If you are an avid skier/snowboarder, you might opt to ignore the warning. 

*****USGS UPDATE*****
While some of this info is now about a week old, USGS has posted the following:

"Earthquake swarm under Mammoth Mountain February 06, 2014

An earthquake swarm under Mammoth Mountain (Mono County, CA), which started slowly on February 3, 2014 intensified in the early hours of February 5 with many small-magnitude earthquakes occurring in rapid succession, a phenomenon known as "spasmodic bursts." The largest earthquake over the ~ 4 hours of heightened activity, a magnitude 3.0, occurred shortly after 1am local time. The swarm is emanating from depths of about 5 km (~ 3 miles) below the surface. Most earthquakes in the swarm are too small to be felt, but the magnitude 3.0 earthquake was felt by a few people in the town of Mammoth Lakes. Presently, earthquake activity beneath the mountain remains above background levels. Earthquake swarms, including spasmodic bursts, occur periodically beneath Mammoth Mountain. The current swarm is notable, however, because it includes the largest magnitude event (M3.0) observed in ~15 years. The attached plot shows the numbers of earthquakes under Mammoth Mountain over the last three months. CalVO deformation monitoring sensors at Mammoth Mountain show no significant change. In the adjacent Long Valley Caldera, the modest, quasi-steady inflation that has been observed for the last couple of years, also appears unchanged by the Mammoth Mountain swarm. CalVO scientists continue to closely monitor seismic, deformation, and gas emission signals."

This statement may not factor in recent changes recorded by their GPS instrumentation as illustrated in an above update. It is interesting to note that USGS does state the swarm is 'notable' due to the magnitude of the 3.0 quake. They are monitoring the volcano more closely now, so if anything, they are in agreement this particular swarm is very interesting, and could pose potential hazards.


*****UPDATE 2/13/2014*****

The main seismic crisis appears to have ended at this time. No new significant quakes are occurring. all quakes for today are well under mag 2.0, so at this point any quakes are likely the result of crustal adjustments. It will be interesting to see whether or not USGS instruments end up picking up an increase in CO2 emissions, or if any instability occurs. At this point, it is unlikely that the small dike intrusion would result in much else. 


Tally of today's earthquake series. 
Add a 2.2 to the list that just occurred... maybe I spoke too soon? Hmm...


*****UPDATE 2/14/14*****
This is probably the last update, as nothing new has happened since yesterday's 2.2 quake. Any further seismicity is probably the result of crust/rock adjustments and no longer related to any magma intrusion. If anything else develops, I'll revisit this post. For now, it looks like the latest, and record setting crisis for Mammoth Mountain is over.

*****UPDATE 2/15*****

8 Quakes over 1.0 just occurred at Mammoth. Two of them were 2.4, and 2.1. Their locations were random compared to the majority of the swarm quakes. Most of the new quakes occurred on the lower SE flank. These are probably crustal adjustment tremors, and not directly related to magma. The volcano will likely have some residual seismicity for the next couple of weeks or months.

                                                           *****UPDATE 2/19/2015*****

The USGS at CalVO has released the following update:

"Earthquake swarm under Mammoth Mountain - Update February 18, 2014

The earthquake swarm under Mammoth Mountain which started on February 3, 2014 has declined over the past few days. The daily numbers of earthquakes, however, are not yet at background levels. Most earthquakes were (are) M1.5 and less. Many are less than 1.0. The largest event detected was a M3.1, which occurred during peak activity on February 5 (event was upgraded from reported M3.0 to M3.1 after further inspection of the data). At 5 AM PST on February 8, a second period of heightened intensity similar to that observed on February 5 started, which persisted for about 1 hour. During the hour of heightened activity on the 8th, four M2.0+ earthquakes occurred, with the largest a M2.4. A few folks on the mountain felt the M2.4. CalVO deformation monitoring sensors on Mammoth Mountain show no significant change. The swarm is likely caused by the migration of deep-seated hydrothermal fluids. The migrating fluid pressurizes and weakens pre-existing faults causing rock to crack, producing earthquakes. Preliminary measurements made last week suggest carbon dioxide emissions at Mammoth Mountain fumarole have not changed notably; additional magmatic gas data await laboratory analysis of samples to be collected by the USGS this week."


Attached plot image from the above USGS update showing the graph of number of quakes.

So it appears that the recent seismicity was NOT the result of a dike intrusion, but was the result of hydrothermal rock fractures at depth. I guess we'll need to wait and see if the data analysis they mention will turn up any surprises, but at this time I am guessing not, since their GPS data seems to be in historical norms, and no drastic rise in gases has been detected otherwise. This will probably be my last update on Mammoth for the time being, as it seems the situation over there is about over. 





9 comments:

  1. Thanks for the update, I'll be watching this one closely for sure.....

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  2. Yes, the webrecorder at 18:00 UTC looked quite active, and the time depth plot looked like things could be approaching the surface

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  3. I'm thinking it could just be the magma chamber cooling and shrinking.

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  4. While in some volcanoes, this would be a possibility, the nature of the quakes moving from a shallow depth, the magnitudes, etc are not typical of a 'cooling and shrinking' chamber. This is likely new magma intrusion given the depths. USGS has sensors on the mountain that measure CO2 emission. If they detect a rise in emissions, it further strengthens that case.

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  5. if you cross check (ie bink compare multiple browser tabs) the WORKING webrecorders near Mammoth Mtn at :

    http://volcanoes.usgs.gov/volcanoes/mammoth_mountain/mammoth_mountain_monitoring_8.html

    it seems apparent that there are several smaller quakes still happening, and the other websites are only doing occasional updates (or only updating the larger quakes in a timely fashion) .

    I suggest stations MMP , MCY , & MRD ( for example ..)

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    Replies
    1. I was just looking at those. Pretty exciting!

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  6. hi:
    Where on the web did you find the nice deformation plot ? The ones I found look like c**p ...

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  7. If you go to http://earthquake.usgs.gov/monitoring/gps/LongValley/ you can click on any number of seismograph/GPS stations to see current data. :)

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  8. this baby is still rockin on 11/02/14

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