Tuesday, August 8, 2017

Is Yellowstone About to Blow?

If you’re being shot at, there is some satisfaction from knowing how often you are being shot at. This holds for volcanoes, even super volcanoes.The last time Yellowstone erupted it left a layer of ash over 20 meters (70 feet) thick some 1,200 kilometers (800 miles) away near Colorado Springs. I know, because I personally pulled a camel's tooth out of the base of the Pearlette Ash deposit there. This was not a trivial eruption, and ash from it has been found in drill-cores on the east coast of the US and in the Gulf of Mexico. It probably killed everything within 1,000 kilometers in all directions.

Q: Do geologists know when Yellowstone might erupt again? It appears to erupt every few hundred thousand years.

The first was: 2,100,000 years ago
Second was: 1,200,000 years ago
And the last one was: 640,000 years ago

Are we in any danger of a fourth one?
- Brandon F

A: Yes - we are very aware of this eruptive periodicity in the USGS Volcano Science Center - we have a full-time volcanologist assigned to Yellowstone as the Scientist-in-Charge (SIC) of the Yellowstone Volcano Observatory. He works in close coordination with seismologists at the University of Utah, and with the US Park Service. Some links might be of interest to you:


Most important from your point of view might be the Yellowstone hazard assessment:

Christiansen, R. L., Lowenstern, J. B., Smith, R. B., Heasler, H., Morgan, L. A., Nathenson, M., Mastin, L. G., Muffler, L. P. & Robinson, J. E. (2007). Preliminary Assessment of Volcanic and Hydrothermal Hazards in Yellowstone National Park and Vicinity. U.S. Geological Survey Open-File Report , 2007-1071, 98 p.
Rest assured that the caldera is closely monitored by several different entities including the USGS. Our experience is that, while you cannot predict an earthquake, you CAN predict a volcanic eruption if you have adequate instrumentation on the volcano. Several of our staff returned just this week from making our periodic gravity and geodetic GPS surveys (these will detect inflation, for instance). The caldera and surrounding terrane are very well-instrumented with telemetered seismometers, also.
The assessment of the SIC is that we are not likely to have a super-eruption in our lifetimes - that's essentially the assessment above. I will excerpt key pieces of it here for you:

"No volcanic eruption has occurred in Yellowstone National Park or vicinity in the last 70,000 years or more."

"One statistical measure of eruption probabilities based on this episodic behavior suggests an average recurrence of 20,000years. The fact that no such eruption has occurred for more than 70,000 years may mean that insufficient eruptible magma remains beneath the Yellowstone caldera to produce another large-volume lava flow."

Table 5. Estimates of annualized probability of events greater than a given magnitude.
Diameter (m)       Area (m2)    Events in last 14 thousand years     Annualized Probability
                >2                           3.1               7000 (estimated)                                   0.50
            >300                  70,700                      16                                                      0.0013
          >2000             3,140,000                        2                                                      0.00014

This last table is from page 83 of the report. The chances for a large hydrothermal eruption next year (NOT a super volcano eruption) is just a bit over 1 in 10,000. For reasons explained above, the probabilities are likely even lower than this.
Bottom line: those in the (detailed) know are not worried.

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