Increased seismic activity at Yellowstone National Park has scientists talking – and prophets of doom all worked up.

Why am I writing about this? Because

1. I have lived the past six months immersed in volcanology research for the novel I’m writing
2. I have a gee-whiz college minor in geology, 15 whopping 200-level credits of formal education in the field
3. I really like Yellowstone and I’d hate to have roast buffalo burger raining down on me here in Seattle

The real expert, Dr. Jacob Lowenstern, Chief Scientist at the Yellowstone Volcano Observatory, says:

The most likely “bad” thing that could happen would be triggering of a larger earthquake or some sort of steam explosion set off beneath the lake. At this point, any kind of volcanic eruption is a long shot. That’s why we haven’t called for a volcano advisory. None of our other monitoring indicators show anything that is nearly so anomalous as the earthquakes. At this point, the most likely thing is that the swarm will continue, perhaps for weeks, and then will end without any other related activity.

First, let’s define our terms.

The seismic activity in question consists of multiple small, brief quakes over a period of time, and is normal for a dormant volcanic site. Average seismic activity at Yellowstone in the last 10 years is 1,000-2,000 tremors a year. Since December 27, the activity level monitored by the Yellowstone Volcano Observatory has increased to hundreds of tremors, approximately 500 during the first week, only three of which were greater than 3.0 in magnitude.

Reports indicate that seismic activity has subsided, and is back to normal levels, for now.

History

The last major earthquake swarm was in 1985 and lasted three months. The observatory said similar swarms have occurred in the past without triggering steam explosions or volcanic activity.

Yellowstone is a supervolcano which last had a major, full-scale eruption 640,000 years ago. That eruption was a class 8 eruption, ejecting 240 cubic miles of rock and dust into the atmosphere and creating today’s Yellowstone Caldera, approximately 35 x 42 miles in diameter.

There have been other significant eruptions since, one as recently as 13,800 years ago – that’s just a blink of an eye in terms of geologic time.

Eruption Indicators

Indicators of in impending eruption can include:

• Increased seismic activity – short and long period earthquakes & harmonic tremors
• Gas emissions – in some cases a buildup, followed by a decrease as magma seals passages
• Ground deformation – as monitored by elevation, tilt, slope & rate of change
• Thermal monitoring – infrared satellite imaging, on-site thermometry
• Hydrology – monitoring wells & boreholes, observing lahars & debris flows
• Satellite-based remote sensing – thermal, ozone, INSaR differential radar
• Mass movements and mass failures – monitoring using remote sensors like satellite imagery and acoustic flow monitors

In addition to the earthquake swarms, they’ve recorded upward movement of the Yellowstone caldera floor at almost 3 inches (7 centimeters) per year for the past three years, which is more than three times greater than previously observed since such measurements began in 1923.

Certainly, Yellowstone is displaying some of these indicators – but not all of them, and not, it seems from past history, an atypical pattern.

Scale of Volcanic Eruptions

Volcanologists have a very handy metric for identifying the scale of a volcanic eruption, the Volcanic Explosivity Index. The one I personally experienced, the 1980 Mt. St. Helen’s eruption, was pretty small potatoes. Others, before and since, have been much more significant – with Yellowstone at the top of the scale.

Prophets of Doom

Because Yellowstone’s original eruption was so spectacular, it’s long been a target for prophets of doom and paranoid survivalists. The following is excerpted from some fairly alarmist material about the possibility of Yellowstone erupting, put together long before this latest earthquake swarm.

If a major eruption of the Yellowstone Supervolcano occurs, everyone within 600 miles should be prepared for the sudden blast. There may be no precursor quakes prior to such a blast. If it blows, there will be no life within 600 miles except those people who have prepared a place underneath the ground. Millions of people would die – most within the surrounding 100 miles. Even airplanes within the area could be blown out of the sky. It will cause an immediate nuclear winter of dirt and ash in the air over the entire world for 2 years. No crops grown in the midwest U.S. for that same period of time. Our emergency services will be overloaded and unable to respond.

Let’s take a look at those statements, one at a time.

First, there aren’t millions of people within a 600 mile radius of Yellowstone, Wyoming – so that death rate is awfully melodramatic. The fatality radius for the Tambora eruption, a class 7, was about 40 miles, so it’s conceivable that a class 8 supervolcano eruption might wipe out all life within a 100 mile radius. Outside that range, the ashfall would be very heavy, but it would conceivably be survivable.

Yes, it’s possible that airplanes could be blown out of the sky, if they were in the exact wrong place at the wrong time. The same could apply to the recent Mt. Pinatubo and Mt. St. Helens eruptions – they both sent explosive clouds of superheated ash, gas and pumice into the stratosphere.

The nuclear winter argument is pretty accurate. In 1815, the class 7 Mt. Tambora eruption spewed 38.5 cubic miles of ash and gas into the atmosphere eruption, and it was known as the “year without a summer” with snow and frosts in June. 1816 was the second coldest year in a century. A supervolcano eruption, sending ten times the ash and rock into the atmosphere, would have proportionately a more severe effect on global climate.

Would US and global emergency services infrastructure be overloaded and unable to respond in the face of such a disaster? Uh, Hurricane Katrina. Hopefully, the powers-that-be had a very constructive lessons-learned session, but still, I’d recommend those in surrounding areas plan for self-reliance, instead.

Is the Sky Falling?

Probably not, per Dr. Lowenstern and host of other experts who are not issuing any kind of volcano watch at this time. The chances of it happening in any given year, in geologic time, are infinitesimal. Really. Relax and take pictures of the geyser.

Resources:

USGS Volcano Site
Wikipedia on Volcanoes