Red Lodge, Montana

Living by a Supervolcano – the Yellowstone Caldera

Science Corner Yellowstone Supervolcano by Gerald Davidson, PhD

The geological history of Montana has been marked by many unusual events, and amazing changes in the climate and environment. The wonders of Montana have been a favorite of geologists for many years. Perhaps this series of short articles may illuminate some of the amazing environmental aspects that are special to Red Lodge.

Red Lodge, by all appearances, is blessed with one of the most wonderful settings in America: lovely streams, forests, high mountains, and not so far away, the marvels of Yellowstone Park. Like those people of Pompeii, nearly two thousand years ago, many of us are unaware that we are living next to a gigantic volcano.

The Yellowstone volcano is one of about a dozen active volcanoes of a type called “resurgent calderas,” with central calderas or craters many miles in diameter. The caldera of Yellowstone is so vast that it was not immediately recognized as a volcano. We are fortunate that none of these monsters has erupted within human history. When they do go off, the effects are global.

A relatively minor eruption of Mt. St. Helens caused massive disruption in the northwest U.S., but that was a puny eruption compared with the largest eruptions of Yellowstone. The famous eruption of Vesuvius was only slightly bigger, but it acquired a special notoriety because it completely buried several cities lying on its flanks. The biggest eruption in the past two hundred years was that of Tambora in Indonesia in 1815. It spewed so much debris into the atmosphere that the climate was cooled by several degrees; the following year saw calamitous crop failures throughout the world. Toba, on the other end of the Indonesian archipelago is another resurgent caldera about the size of Yellowstone; its last known eruption is suspected of causing a “bottleneck” in human evolution, reducing human populations to several thousand. Toba ejected a thousand times as much ash and debris as the eruption of Mt. St. Helens. It may be just luck that we are still here.

Only in that past fifty years have geologists begun to understand the Yellowstone volcano and its remarkable setting. The western U.S. has an unusually large number of resurgent calderas, of which Yellowstone and the Long Valley Caldera in California are known to be still active. As noted by one geologist, Yellowstone has erupted regularly every 600,000 years; the last eruption was 600,000 years ago!
The Yellowstone Volcano is believed to lie atop a “hot spot” deep within the earth. We are actually drifting across the hot spot at a rate of about 2.5 inches per year. From our vantage point, it appears that the volcano first appeared in Oregon and has popped up about a dozen times along the way to its present location – each time burying entire mountain ranges. It seems to be headed for Red Lodge, but at the moment it has run into a somewhat more resistant mass of mountains. So perhaps the volcano won’t pop up under our feet for the next million years.

But an eruption from the present caldera is a real possibility. What would it be like? For one thing, we would probably have many signs of danger before the lid came off. The people of Pompeii had many signs of an impending eruption, but they didn’t have teams of volcanologists monitoring the vital signs, as we now have for the most dangerous volcanoes around the world. But we can’t be absolutely certain, for no one has actually seen a truly gigantic volcanic eruption. It could erupt after several years of earthquakes and other precursors, or the eruption might happen within several days. That’s not a lot of time to pack up and get the heck out of here.

Many of the people in Pompeii were killed instantly by pyroclastic flow rushing down the mountainside at temperatures comparable to a hot oven. They, however, were living only a few miles from the volcano. Pyroclastic flows reaching Red Lodge, 50 miles away, are unlikely – but not impossible.

For nearby locations ash falls would be the primary hazard. By “nearby,” perhaps we should think of places within several hundred miles! The last eruption of Krakatoa produced ash falls hundreds of miles away, causing total darkness for days. Depending on the winds, Red Lodge might be buried under as much as several hundred feet of ash. If the city had the same bad luck as Pompeii, it might be forgotten and rediscovered a thousand years later! (Just assume a posture that will make a nice display in a museum.)
But being buried under ash might be a gentler end than suffering the potential climate impacts of a monster eruption. The “moderately large” eruption of Tambora probably caused the loss of millions of lives through famine and disease. A sudden cooling of the climate by a full-scale eruption of Yellowstone would undoubtedly cause global hardship. Many countries have vast reserves of grain and other foods that might last through a hard year; but a climate catastrophe resulting from an Yellowstone eruption could last several years.

What to do? There’s virtually no way we could prepare for an eruption of Yellowstone. But Montanans love to take risks, so perhaps we should just sit where we are and meditate on the fact that we are probably at not much greater risk than the rest of the planet.

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