Since the start of February, Yellowstone National Park and its supervolcano have been hit with a wave of at least 20 earthquakes and a number of smaller tremors. Although the largest earthquake only registered a 2.9 on the Richter scale and all have struck about five miles below the Earth’s surface, this so-called earthquake swarm is noteworthy – though likely not cause for alarm. “While it may seem worrisome, the current seismicity is relatively weak and actually represents an opportunity to learn more about Yellowstone,” wrote researchers Michael Poland and Jamie Farrell for the Yellowstone Volcano Observatory. “It is during periods of change when scientists can develop, test, and refine their models of how the Yellowstone volcanic system works.”
Though the name may conjure images of aggressive insects, earthquake swarms are actually a fairly common, benign occurrence at Yellowstone. The largest earthquake storm came in 1985, when more than 3,000 earthquakes struck Yellowstone over several months. The area typically experiences 1,000 to 3,000 earthquakes each year, most of which are not felt. Swarms are caused by stress changes at fault lines due to either tectonic forces or local pressure increases resulting from changes in water, magma, or subterranean gas. The highly seismic Yellowstone is affected by both swarm-causing factors.
While the earthquake swarms and Yellowstone’s supervolcano are both currently harmless, there is always a small chance that, someday, the big one will arrive. The U.S. Geological Survey estimates that there is a 1 in 730,000 chance that the supervolcano will experience a major eruption; this is roughly equivalent to the probability of an asteroid collision with Earth. As for what might trigger such an event, tiny tremors serve as reminders. Seismologist Jamie Farrell told National Geographic, “The most likely hazard in Yellowstone is from large earthquakes”.