An earthquake registering a magnitude 4.8 shook the northwest corner of Yellowstone National Park Sunday, causing more alarm than damage. As far as the latter is concerned, none was immediately reported, nor were there any apparent injuries. Seismologists say it was the biggest recorded earthquake at Yellowstone in 34 years, leading some to worry if it was just the precursor to “the big one.”
Reuters reported (via Yahoo News) March 30 that geologists at the University of Utah Seismograph Stations said in a statement that the tremor, which was considered relatively minor on a seismic scale, was the largest of a flurry of small quakes that struck Yellowstone beginning on Thursday. It hit near the Norris Geyser Basin and was felt as far as 23 miles away in the towns of Gardiner and West Yellowstone, small Montana towns that are located adjacent to the two of the entrances to the national park.
Although no injuries were reported, people did report shaking, sort of like when tractor-trailer trucks roll by. Items on grocery store shelves also reportedly were dislodged.
Yellowstone National Park sits atop the Yellowstone Caldera, a super-volcano that has lain relatively dormant for nearly 650,000 years. Seismologists just recently learned that the caldera itself in 2.5 times larger than was previously believed. The massive magma chamber that makes up the caldera measures some 30 miles wide.
According to the Yellowstone Volcano Observatory, which monitors seismic activity around the caldera, the latest tremor was not historically out of the ordinary. The national park sees from between 1,000 and 3,000 earthquakes each year.
University of Utah seismologists noted that Sunday’s large earthquake occurred near the center of an area of ground uplift that geologists have been observing for several months. The recent spate of activity is also linked to the uplift. The uplift itself is caused by the rising molten rock under the Earth’s crust. (Note: It is the molten rock that generates the heat that powers the geothermal wonders of Yellowstone National Park, like Old Faithful, the world-famous geyser that erupts every 91 minutes and draws millions of tourists every year from around the world.)
Still, even with all the recent activity, the number and magnitude of the earthquakes are well within historic norms, leaving no indication that they might portend a massive eruption.
The fear of a Yellowstone eruption comes from the geological evidence that a cataclysmic eruption occurred at the super-volcano site some 2 million years ago. That eruption, according to the Yellowstone Volcano Observatory, was known as the Huckleberry Ridge eruption, covered half of North America in ash and killed plants and animals as far south and west as the modern-day Mexican border, as far east as central Iowa, and as far north as the Canadian border. The latest massive eruption, call Lava Creek eruption, although not as powerful, deposited ash over an even larger area of what is the present U. S., extending, in addition to the same areas covered by the Huckleberry Ridge eruption, even further southeastward into modern-day western Mississippi.
The last eruption of Yellowstone occurred 70,000 years ago, which basically consisted of rhyolitic (light-colored, high silica content volcanic rock) lava flows.