About 2.1 million years ago the earth witnessed perhaps the single greatest volcanic event in its five billion year life span. It was an eruption so colossal that it ejected over 600 cubic miles of debris over the surrounding landscape and altered global temperatures and weather patterns for years. So where was this cataclysmic explosion? Asia? No. Indonesia? Nope. Africa? Uh-uh.
Try near Idaho Falls.
Oh, and it's probably going to happen again.
Anybody who has ever been to Yellowstone National Park can tell you about the area's geological highlights; the scalding pools, the bubbling mud pots, and of course, the geysers. But what many visitors to the park don't realize is the sheer magnitude of the park's pre-modern geology—and the potential scale of future eruptions.
At the root of Yellowstone's fantastic natural beauty lies a fissure in the earth's crust. A leak, if you will, that allows the immensely hot, liquefied rock near the earth's core to seep up toward the surface. Initially, this melted rock, or magma, is thought to travel through a narrow chimney-like opening. But as it approaches the surface, the magma spreads out and collects in an area about thirty miles long, thirteen miles wide and six miles deep, forming an immense magma chamber the top of which is just five miles below the feet of all those camera-toting tourists.
Geologists call these fissures "hot spots" and they are apparently exceedingly rare. The Hawaiian Islands and Iceland are products of hot spots, though they are without the gigantic magma chamber that accompanies Yellowstone's hot spot.
Indeed, it is this seething, roiling magma chamber that allows Yellowstone to be included on the short list of earth's super volcanoes. As rare as hot spots are, super volcanoes are even rarer, geologically speaking. The last known eruption of a super volcano happened about 74,000 years ago on the island of Sumatra in present-day Indonesia. According to scientists, this explosion was likely the loudest sound ever heard by human beings. The force of the blast ejected about 700 cubic miles of debris, along with great quantities of sulfur and other gases that quickly dispersed around the planet. The effects on global temperature and weather patterns were immediate and long lasting. One theory even suggests that this eruption may have had nearly disastrous consequences for the human species, perhaps killing all but a few thousand of the planet's early population of Homo sapiens.
In comparison, the largest of Yellowstone's eruptions, the Huckleberry Ridge event, occurred about 2.1 million years ago and covered an area roughly half the size of the United States with ash at least a foot deep and threw lesser quantities much farther. Combined with the two other major Yellowstone eruptions, Mesa Falls and Lava Creek, enough material has been ejected from the Yellowstone Caldera to fill the Grand Canyon.
It should come as little surprise then that a similar eruption at Yellowstone would have immediate and cataclysmic effects on not only the region and the nation, but the planet as a whole.
Geologically speaking, the term "recent" could refer to anything happening during the last 100,000 years or more. However, even from one year to the next, scientists observe subtle changes in the geology of Yellowstone. Most of these changes are not apparent to the casual tourist, and while interesting, may not necessarily indicate anything abnormal over the short-term. Then again, it just might.
One widely reported feature that has received its share of media hype is the so-called "bulge" forming under Yellowstone Lake. According to the United States Geological Survey (USGS), this feature, which is about 2,000 feet long and rises about 100 feet from the bottom of the lake, may have existed for many decades and has not shown any measurable change over the last few years since its discovery. Geologists with the Yellowstone Volcanic Observatory believe it is the result of accumulated gases associated with Yellowstone's active hydrothermal system. They say there is no immediate danger to park visitors or people who live nearby.
In other recent news that may or may not portend the end of modern civilization, a group of bison were found dead near an area known as the Norris Geyser Basin in March of last year, presumably after being exposed to toxic geothermal gases. While such occurrences are rare, they have reportedly happened several times during the park's 132-year history.
Four months after the bison were discovered, the Norris Geyser Basin was closed to the public after park staff noticed increased activity around a few of the geysers. Apparently, geysers that had previously been dormant for several years became active again. The Norris Geyser Basin area was reopened to the public in October.
NOT "IF" BUT "WHEN"
The regularity of Yellowstone's geysers is legendary; even the name of the park's biggest attraction, Old Faithful, recognizes the apparent punctuality nature can display when so inclined. It also seems that Yellowstone's more impressive geologic occurrences follow a similar, albeit much slower, schedule. Looking back over the geologic record, Yellowstone's eruptions seem to occur at roughly 650,000-year intervals. The last Yellowstone eruption, the Lava Creek event, was about 640,000 years ago. According to some, that makes Yellowstone just about due for another super eruption.
So does all this mean an eruption is imminent? As with nearly everything, it all depends on whom you ask. Geologists believe that the Yellowstone hot spot is simmering down after going strong for the last 16.5 million years, though at this point no one is counting out another globally destructive eruption quite yet.
Geological phenomena such as earthquakes and volcanic eruptions are famously difficult, if not impossible, to predict with any certainty. Complicating the matter in this case is the fact that no one has ever seen a super volcano in action before. In spite of all these questions one thing remains almost certain, the Yellowstone Caldera is likely to explode again on a scale never before seen by modern man. The only real question is: When?