Old Unfaithful

Anthony Watts is watching seismic activity in Yellowstone Park, which sits on top of a supervolcano.

You have already heard that there has been increased seismic activity at Yellowstone National Park over the last few days. Since December 26th, there have been several earthquakes a day, some jut over 3.0 magnitude, in the vicinity of the north side of Yellowstone’s lake. This is a seismically active region, but the level of earthquake activity being seen now is much greater than seen in perhaps decades (though the data are still not sufficiently analyzed to make positive comparisons yet).Volcano experts have absolutely no clue as to what this means. A major reason for virtually total uncertainty is that Yellowstone sits on top of a very large caldera of the type that is formed by a so-called “super volcano” and the last super volcano to erupt was a few years (like, 70 or so thousand years) before any seismic or other geological monitoring station were set up anywhere. Indeed, the first really serious data collection at Yellowstone began just over 30 years ago.

Wikipedia describes the last eruption at Yellowstone this way:

The last full-scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened approximately 640,000 years ago, ejected approximately 240 cubic miles (1000 cubic kilometres) of rock and dust into the sky.

Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages ±0.6 inches (about ±1.5 cm) yearly, as an indication of changes in magma chamber pressure.

The upward movement of the Yellowstone caldera floor – almost 3 inches (7 centimeters) per year for the past three years – is more than three times greater than ever observed since such measurements began in 1923. From mid-Summer 2004 through mid-Summer 2008, the land surface within the caldera has moved upwards, as much as 8 inches at the White Lake GPS station. The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory “see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable.

The eruption of 640,000 years ago would have ejected 800 times more material than Mount St Helens in 1980. “The 1980 eruption of Mount St. Helens, a composite volcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the most significant to occur in the contiguous 48 U.S. states (VEI = 5, 0.3 cu mi, 1.2 km3 of material erupted), in terms of power and volume of material released, since the 1915 eruption of California’s Lassen Peak.” (240 cu miles/.3 cu miles=800)