Thursday’s 5.8-magnitude earthquake in western Montana was the strongest to hit the state in 60 years, and it quickly raised fears that the nearby Yellowstone supervolcano had awoken from its long slumber. But Montana residents can rest easy: While the Yellowstone volcano is active, a common earthquake is unlikely to have an effect on this ancient cauldron of superheated rock.
Still, local fears are understandable: The temblor struck early on the morning of July 6, some 230 miles from Yellowstone National Park, and was accompanied by at least 10 lesser quakes. It was the region’s strongest earthquake in over a decade, but although the shaking startled residents, scientists quickly determined that it didn’t represent the ominous rumblings of an awakening supervolcano. The U.S. Geological Survey’s seismic sensors immediately identified the quake’s culprits, which were slipping faults — fractures in the Earth’s crust — and not a threatening reservoir of pressurized magma, waiting to explode out of the ground.
Scientists, however, certainly believe that the massive Yellowstone volcano, whose rim measures 30 miles long by 45 miles wide, has a catastrophic potential far greater than anything mankind has ever experienced before. It’s just not likely to reveal it anytime soon.
Quakes as intense as the one Montana just experienced are unsettling, but this earthly rousing is geologically commonplace. Yellowstone National Park experiences between 1,000 and 3,000 earthquakes each year, revealing an active volcanic world beneath one of America’s most popular national park destinations. The park’s heat-propelled geysers and dangerous thermal pools also hint at the hot magma brewing below.
But all that activity does not portend an eruption, large or small. Though scientists will never rule out the possibility of an eruption entirely, decades of everyday monitoring have revealed no signs of a looming eruption. According to the Yellowstone National Park’s website:
Another caldera-forming eruption is theoretically possible, but it is very unlikely in the next thousand or even 10,000 years. Scientists have also found no indication of an imminent smaller eruption of lava.
Signs of volcanism at or around Yellowstone, the park notes, should be expected:
As at many caldera systems around the world, small earthquakes, ground uplift and subsidence, and gas releases at Yellowstone are commonplace events and do not reflect impending eruptions.
If an eruption was imminent, scientists expect the buildup to be more extreme, something that would be detectable for weeks or even years. This would include massive deformations of the land around the park (think abruptly formed canyons) and a continued onslaught of earthquake swarms, perhaps jolting the area each day.
Lava last gushed out of the Yellowstone supervolcano around 70,000 years ago, and in the last two million years, scientists believe that three “major” volcanic eruptions occurred. One of these, the Island Park super-eruption, left a telltale blanket of volcanic rock in the area about two million years ago, and scientists estimate that this event produced 2,500 times more ash than the 1980 Mount St. Helens eruption. This geologically puny eruption, it should be noted, leveled a forest, tossed trees around like toothpicks, blew the top off a mountain, caused over a billion dollars in damage, and dumped ash onto 11 U.S. states and five Canadian provinces.