The recent earthquake swarm at Yellowstone is not an indication of unusual volcanic activity. Earthquake swarms are normal geologic events at active volcanic systems. US Geological Survey vulcanologists who specialize in studying Yellowstone have determined that the volcano alert level there is normal.
About the author - I have a PhD in geochemistry from UCLA.
I was the lead author of the Nuclear Regulatory Commission's research plans for assessing the safety of high level waste disposal at Yucca Mt. Nevada. A critical research area I developed and managed research investigations on was assessment of geologic hazards at Yucca Mt. volcanic hazards assessment is is critical research area we studied at Yucca Mountain.
The University of Utah and the USGS stated on December 29 that volcanic conditions were normal. The recent earthquake swarm is no cause for concern.
YELLOWSTONE VOLCANO (CAVW#1205-01-)
44.43°N 110.67°W, Summit Elevation 9203 ft (2805 m)
Volcano Alert Level: NORMAL
Aviation Color Code: GREEN
The University of Utah Seismograph Stations reports that a notable swarm of earthquakes has been underway since December 26 beneath Yellowstone Lake in Yellowstone National Park, three to six miles south-southeast of Fishing Bridge, Wyoming. This energetic sequence of events was most intense on December 27, when the largest number of events of magnitude 3 and larger occurred.
The largest of the earthquakes was a magnitude 3.9 (revised from magnitude 3.8) at 10:15 pm MST on Dec. 27. The sequence has included nine events of magnitude 3 to 3.9 and approximately 24 of magnitude 2 to 3 at the time of this release. A total of more than 250 events large enough to be located have occurred in this swarm. Reliable depths of the larger events are up to a few miles. Visitors and National Park Service (NPS) employees in the Yellowstone Lake area reported feeling the largest of these earthquakes.
Earthquakes are a common occurrence in the Yellowstone National Park area, an active volcanic-tectonic area averaging 1,000 to 2,000 earthquakes a year. Yellowstone's 10,000 geysers and hot springs are the result of this geologic activity. A summary of Yellowstone's volcanic history is available on the Yellowstone Volcano Observatory web site (listed below). This December 2008 earthquake sequence is the most intense in this area for some years and is centered on the east side of the Yellowstone caldera. Scientists cannot identify any causative fault or other feature without further analysis. Seismologists continue to monitor and analyze the data and will issue new information if the situation warrants it.
Moreover, if there is an eruption it is not likely to be a huge caldera forming one. A recent USGS report (PDF)has estimated the probability at less than one in a million.
Although the probability of a large caldera-forming eruption at Yellowstone is exceedingly small, it is exceedingly difficullt to make a defensible quantitative estimate of that probability. As there have been three such eruptions in about the past 2,100,000 years, there are only two intereruptive periods from which to gauge any additional possible interval between the third and a potential fourth such event.
The first interval, between the Huckleberry Ridge (2.059±0.004 Ma)
and Mesa Falls (1.285±0.004 Ma) caldera-forming events, was 774,000±5700 years. The second interval, between the Mesa Falls and Lava Creek (0.639±0.002 Ma) events, was 646,000±4400 years.
A statement, widely repeated in popular media, regards such eruptions as occurring at Yellowstone "every 600,000 years" with the latest eruption having been "600,000 years ago". This is commonly taken to imply that another such eruption is "overdue".
Such a statement is statistically indefensible on the basis of the extrapolation of two intervals
There have been 17 major rhyolitic eruptions in the last 170,000 years. The small likelihood of a one in 10,000 year eruption is about a hundred times greater than the one in a million or less chance of a caldera forming eruption.
At least 17 large rhyolitic lava flows, most of them with volumes of 10 km3 or greater, have erupted within the Yellowstone caldera during about the past 170,000 years (Christiansen, 2001).
Stratigraphically they belong to the Central Plateau Member of the Plateau Rhyolite. Each of these lava flows extruded through one of two linear vent zones that cross the caldera along the extrapolated positions of extracaldera tectonic fault zones (figs. 8, 11), and activity has been
essentially contemporaneous on both zones. The largest of these lava flows cover areas greater than 350 km2 and have volumes greater than 30 km3 (table 2)
Earthquake swarms at Long Valley Caldera caused concerns a few years ago but there was no eruption. Earthquake swarms are not necessarily followed by eruptions of any kind. They are normal. There is a very specific type of low frequency seismic signature called volcanic tremor that is associated with rising magma. That was not reported at Long Valley and it hasn't been reported at Yellowstone.
Long Valley is a caldera system similar to Yellowstone that had the most recent "supervolcano" eruption. As huge as that eruption was, it did not wipe out life or change the climate.