December 11, 2009
If the current earthquake activity in the Yellowstone National Park continues to increase, the fragile caldera could collapse in on itself, opening up the pressurized magma and causing an explosion with ash and debris that would destroy crops and impede life all the way to New York City.
Mild tremors in the Yellowstone National Park are not rare. The region, with its geysers, like “Old Faithful,” and thermal pools has long been known as an area of geological instability. Despite the lack of a cone-shaped mountain or obvious volcano, scientists now know that almost the entire Yellowstone area is an enormous caldera.
There is ample evidence of huge volcanic explosions from the Yellowstone volcano in the past. Ash deposits reveal the eruptions happen with some periodicity and note the last catastrophic explosion was just 70,000 years ago. According to these geologic records, we are long overdue for the next “big one.”
With the discovery that this huge caldera exists, scientists were startled to learn that the surface of the caldera is bulging. Last year a report in the journal Science found the park’s central region was rising up at a rate of up to 7cm a year due to the movement of a pool of magma several miles below the surface. Scientists measured over two feet of uplift during the period 1923-1985.
This suggests that the underlying magma may be building up just below the surface of the land, preparing for a major “super-volcano” event. But as they carefully monitored the seismic activity in the region, they were comforted by the relative stability of both the frequency and number of earth tremors. But that has just changed.
More than 250 tremors have been recorded since Friday, December 26th, 2008, including nine greater than magnitude 3.0 on the Richter scale, according to the University of Utah. The largest, a magnitude 3.9, struck on Saturday and the area was shaken by a 3.3 tremor just after midday on Monday, December 29th.
While earthquakes are common in the giant park, which covers parts of Wyoming, Idaho and Montana and experiences about 1,000 to 2,000 tremors a year, the intense burst of seismic activity lasting several days is being described as “unusual.”
“They’re certainly not normal,” said Robert Smith, a professor of geophysics at the University of Utah. “We haven’t had earthquakes of this energy or extent in many years.”
Mr Smith, director of the Yellowstone Seismic Network, which operates seismic stations around the park, said the earthquakes have ranged in strength from barely detectable to Saturday’s 3.9. A magnitude 4 earthquake is capable of producing moderate damage. But the threat of earthquakes pales compared to what most scientists fear most — the collapse of the caldera and the ingnition of a super-volcano.
“This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to,” he said. “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.”
So far, all the quakes have been centred beneath the northwest end of Yellowstone Lake. No damage has been reported and a park spokeswoman said there does not yet appear to be cause for alarm.
Mr Smith said it was difficult to say what might be causing the current tremors. He added that the park’s famous geysers and hot springs were a reminder of the magma underground which turns ground water to steam.
“That’s just the surface manifestation of the enormous amount of heat that’s being released through the system,” he said.
In 1959, a magnitude 7.5 earthquake near Hebgen Lake just west of Yellowstone National Park triggered a landslide that killed 28 people. If the current earthquake activity continues to increase, the fragile caldera could collapse in on itself, opening up the pressurized magma and causing an explosion with ash and debris that would destroy crops and impede life all the way to New York City.
Is this happening now before our eyes? We’ll have to wait and see.