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Long Valley Caldera Is This California Supervolcano a Ticking Doomsday Time Bomb?

Updated on January 6, 2013

A Tale of Two Volcanic Goliaths

One of the most dangerous volcanoes in America may very well be one that few have ever heard of. Everyone knows about the Yellowstone supervolcano, but do you know about its equally dangerous little sister -- the Long Valley Caldera in California? In fact, the Long Valley supervolcano is actually far more active than the Yellowstone Caldera and is considered by scientists to pose a much higher risk for a catastrophic eruption.

The good news, at least for those who are living the prepping lifestyle, is that if you are prepared for one doomsday supervolcano eruption, then you are prepared for the other. However, it is important to understand this California volcano in order to fully understand and appreciate the tremendous degree of risks we face in America. While many argue that the likelihood of a Yellowstone eruption are very low, those risks rise significantly when you realize America is home to not one but two supervolcanoes - and one of them is now showing significant signs of coming back to life.

Long Valley Caldera in eastern California (here viewed from its southwest rim toward its northeast rim on the horizon 18 miles away) was formed about 760,000 years ago in a violent volcanic eruption that blew out 150 cubic miles of magma from beneath
Long Valley Caldera in eastern California (here viewed from its southwest rim toward its northeast rim on the horizon 18 miles away) was formed about 760,000 years ago in a violent volcanic eruption that blew out 150 cubic miles of magma from beneath

Basic Facts about the Lake Valley Caldera

The Long Valley Caldera is a 16 x 32-kilometer oval-shaped depression situated along the east side of the Sierra Nevada Range (just east of Yosemite National Park) in east-central California - 20 kilometers south of Mono Lake. The caldera was formed during a massive super eruption approximately 760,000 years ago that deposited a layer of ash as far east as the Mississippi River and cast the world into darkness similar to a nuclear winter.

Beginning in the late 1970s the supervolcano began manifesting signs that it was once again returning to life, including a strong earthquake swarm in May of 1980 that was located in the southern margin of the Long Valley Caldera. The swarm included four magnitude 6 earthquakes. Additionally, these quakes were associated with a dome-shaped uplift of the caldera floor. These events signaled the beginning of the latest period of caldera activity -- activity that continues to this present day. This ongoing activity at the Long Valley Caldera also includes frequent earthquake swarms, continued doming of the central section of the caldera, the die-off of trees, the release of carbon dioxide gas and changes in hydrothermal behaviors.

These signs have caused the U.S. Geological Survey (USGS) to assign the Long Valley Caldera a threat level of "High to Very High."

The Long Valley Caldera

The Long Valley Caldera
The Long Valley Caldera

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Toba Caldera in Sumatra, Indonesia
Toba Caldera in Sumatra, Indonesia

Volcanology 101: The Power of Supervolcanoes

Supervolcanoes are capable of ejecting more than 240 cubic miles of material -- thousands of times more than "normal" volcanic eruptions. These massive eruptions are rated as magnitude 8 on the Volcanic Explosivity Index (VEI), earning them the ominous label "super eruptions."

A VEI-8 eruption involves the ejection of 1,000 cubic kilometers (240 cubic miles) of Dense Rock Equivalent (DRE) material or more. A VEI-7 eruption involves the ejection of ejection of between 100 and 1,000 cubic kilometers (greater than 24 cubic miles) of DRE material.

The Lake Toba super eruption around 74,000 years ago (the most recent super eruption on earth) at the Toba Caldera in Sumatra, Indonesia, ejected an estimated 2,800 cubic kilometers of DRE material. The Yellowstone supervolcano has had at least four major eruptions: 6,000,000 years ago (1,500 cubic kilometers of DRE ejecta), 4,500,000 years ago (1,800 cubic kilometers of DRE ejecta), 2,100,000 years ago (2,500 cubic kilometers of DRE ejecta), and 640,000 years ago (1,000 cubic kilometers of DRE ejecta).

The Long Valley supervolcano erupted just prior to the most recent Yellowstone eruption (around 760,000 years ago) and ejected an estimated 600 cubic kilometers of DRE ejecta - ash that reached as far east as the Mississippi River.

To put this in perspective, the 1980 eruption of Mount St. Helens, a VEI-5 eruption, ejected only 1.2 cubic kilometers of DRE material. Even the massive eruptions of Mount Pinatubo (1991) and Krakatoa (1883) were only VEI-6 eruptions, ejecting a paltry 10 cubic kilometers and 25 cubic kilometers of DRE respectively!

And, unlike Yellowstone, the Long Valley Caldera has been active in the past 2,000 years. Furthermore, all but three of the approximately 20 Long Valley minor eruptions over the past 8,000 years have been explosive (rather than effusive) in nature.

Recent Activity: Is the Long Valley Supervolcano Roaring Back to Life?

The Long Valley Caldera began to experience ongoing geologic unrest in 1978, when a magnitude 5.4 earthquake struck 6 miles southeast of the caldera. This quake ended two decades of low tremor activity in eastern California. The area has since experienced numerous swarms of earthquakes, especially in the southern part of the caldera.

The most intense of these swarms occurred in May 1980 and included four strong magnitude 6 shocks, three of which struck on the same day. Immediately following this outbreak of quakes, scientists from the USGS mounted a serious effort to reexamine of the Long Valley area. What they detected was troubling to say the least. In addition to the seismic evidence of unrest, they discovered a dome-like uplift in the caldera.

In fact, their measurements showed that the center of the caldera had risen almost a foot since the summer of 1979, following decades of caldera stability. According to the USGS, this continuing swelling, which by early 2000 totaled nearly 2.5 feet and affected more than 100 square miles, is caused by new magma rising beneath the caldera.

However, it didn't end there. During the early 1990s, trees began dying off at several places on Mammoth Mountain, located on the southwest edge of Long Valley Caldera. Studies conducted by USGS and U.S. Forest Service found that the trees were being killed (and continue to be) by large amounts of carbon dioxide (CO2) gas seeping up through the soil from magma deep beneath Mammoth Mountain.

All of this geological unrest (e.g., volcanic gas emissions, earthquake swarms and ground swelling) commonly precede volcanic eruptions. Although recent studies indicate that only about one in six such episodes of unrest at large calderas worldwide actually culminates in an eruption (a probability that is not very reassuring in itself), the USGS continues to maintain that the possibility exists that geologic unrest (such as that which is currently occurring) in the Long Valley area "could take only weeks to escalate to an eruption."

What Does the Future Hold for the Long Valley Caldera?

The USGS places the odds of an eruption at the Long Valley Caldera in any given year at less than one percent. However, one should bear in mind that this is the same odds in any given year of a magnitude 8+ earthquake occurring along the San Andreas Fault. Furthermore, scientists at the USGS readily admit that increased volcanic unrest (like earthquake swarms, ground deformation, and CO2 gas emissions) in the Long Valley area since 1978 significantly increases the chance of an eruption occurring in the near future.

Whether you are preparing for a Yellowstone super eruption or another doomsday scenario, the Long Valley supervolcano only serves to demonstrate how very real the need for such prepping is.

It doesn't matter whether you correctly identify the exact type of future disaster. Rather, what matters is that you prepared in advance at all. Nobody expects a catastrophic disaster to happen, but they invariably do. And when they do, those that seized the opportunity to prepare ahead of time are the ones with the highest probability of survival.

Now you simply have one more reason to continue improving your disaster preparedness, or to make the decision to join the ranks of the growing prepper movement. You can argue about the specifics of any dozen of potential causes, but what you no longer can afford to do is pretend that no threats exist.

Is It All Just Hype? - Let's Get Ready to Rumble...

Is all the talk about looming super eruptions just hype or do these volcanic monsters really pose a credible threat to us?

More Information about the Long Valley Caldera

Long Valley Caldera Activity Update

USGS Volcano Hazards Program

California Volcano Observatory (CalVO)

Report Date: Monday, December 17, 2012

Reporting Period: November 1, 2012 through November 30, 2012

Long Valley Caldera and Mono-Inyo Chain: Thirty-eight earthquakes occurred in the southern half of the Long Valley Caldera (all M<2.0); One earthquake was detected north of Long Valley Caldera in the Mono Basin east of Mono Lake (M=1.3); Four earthquakes of magnitude M=1.0 or greater (largest was M=1.4) were detected under Mammoth Mountain. [Note: Typical high level of seismicity observed south of the caldera in the Sierra Nevada range. Largest event was M=3.0]. Additionally, analysis of continuous GPS data over the last month shows that the persistent modest inflation occurring within the caldera over the past year may be leveling off (see previous updates).

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Report Date: Wednesday, November 14, 2012

Reporting Period: October 1, 2012 through October 31, 2012

Long Valley Caldera and Mono-Inyo Chain: Forty-four earthquakes occurred in the southern half of the Long Valley Caldera east of the town of Mammoth Lakes (the largest was M=2.6); Two earthquakes were located north of Long Valley Caldera, one east of Mono Lake in Mono Valley and another under Mono Craters due east of June Lake (both M<2.0); Eight earthquakes of magnitude M=1.0 or greater (largest was M=1.8) were detected under Mammoth Mountain. [Note: Typical high level of seismicity observed south of the caldera in the Sierra Nevada range. Largest event was M=2.6]. Additionally, analysis of continuous GPS data over the last several months show continued modest inflation within the caldera. Ground motion is directed upward and away from the caldera's center, with a maximum uplift rate between 2 and 3 cm/yr. Horizontal deformation is similar in magnitude, with a N/S extension rate across the caldera's center of about 3 cm/yr. These rates of deformation are comparable to those observed in 2002-2003, and well below the rates seen in the late 1990s.

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Report Date: Monday, October 1, 2012

Reporting Period: September 1, 2012 through September 30, 2012

Long Valley Caldera and Mono-Inyo Chain: Eight earthquakes occurred in the southern half of the Long Valley Caldera east of the town of Mammoth Lakes (largest events was M=1.9); Two earthquake were located east of Mono Lake in Mono Valley (M=1.95 and M=1.7); Six earthquakes of magnitude M=1.0 or greater (largest was M=1.4) were detected under Mammoth Mountain. [Note: Typical high level of seismicity observed south of the caldera in the Sierra Nevada range. Largest events were M=2.6 and M=3.0]. Additionally, analysis of continuous GPS data over the last several months show continued modest inflation within the caldera. Ground motion is directed upward and away from the caldera's center, with a maximum uplift rate between 2 and 3 cm/yr. Horizontal deformation is similar in magnitude, with a N/S extension rate across the caldera's center of about 3 cm/yr. These rates of deformation are comparable to those observed in 2002-2003, and well below the rates seen in the late 1990s.

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What natural or man-made disaster do you think folks should be preparing for?

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    • profile image

      Emilee46 

      5 years ago

      thank.s for the info. you have agreat lense

    • TolovajWordsmith profile image

      Tolovaj Publishing House 

      5 years ago from Ljubljana

      We are living on the bomb!

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