Scientists at Yellowstone National Park are carefully monitoring a series of recent quakes, but insist that there is current no reason to believe that the area is going to blow. Yellowstone, home to famous geysers and hot springs, is among the most geologically active sites in the continental U.S.
Massive eruptions have already occurred three times at Yellowstone, 2.1 million, 1.3 million and 640,000 years ago. The last eruption sent 240 cubic miles of debris and ash into the air, enough to block out the sun over the continental U.S. for a prolonged period of time and cause extinction of species. A new eruption could one day blanket the U.S. in a choking cloud of ash.
Scientists have observed over the past several decades a gradual swelling of the Yellowstone caldera of approximately 0.6 inches per year, indicating magma pressure. Over the last three years, the rate of swelling has increased dramatically to approximately 3 inches per year.
Spooked by the swelling magma, many are fearful that a series of recent quakes which have rocked the region are a precursor to an eruption. Not necessarily so, say scientists. They say that the earthquakes are not induced by magma, but rather by hydrothermal fluids, and are thus not a predictor of eruptions. Still they are closely monitoring the quakes for fear that they could trigger an eruption.
The largest quake storm appeared in 1985, with over 3,000 quakes over several months. The current swarm and the 1983 swarm are classed as "small swarms" as they consist of less than 1,000 quakes. The 1983 swarm consisted of 70 some quakes, while the ongoing current swarm has seen 250+ quakes.
Robert Smith, a professor of geophysics at the University of Utah says that while quakes and quake swarms are a fact of life at Yellowstone, the very short period over which these quakes have occurred has scientists on high alert. Scientists are watching Yellowstone carefully for the sudden dramatic changes in earth shape or the release of smoke which could indicate an eruption is imminent.
Professor Smith describes the recent quakes saying, "They're certainly not normal. We haven't had earthquakes in this energy or extent in many years."
The strongest quake thus far in the current swarm has been 3.8 in magnitude. A magnitude of 4 is sufficient to produce moderate damage to surrounding structures. Says Professor Smith, "This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to. We might be seeing something precursory. Could it develop into a bigger fault or something related to hydrothermal activity? We don't know. That's what we're there to do, to monitor it for public safety."
The quakes have been occurring primarily centered on the northwest end of Yellowstone Lake.
Even if fears that an eruption is impending go unrealized, the quakes themselves could pose a danger. In 1959 a 7.5 magnitude quake near Hebgen Lake triggered a landslide, which killed 28 people.