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Established in 1872, Yellowstone is the oldest national park in the United States (and in the world). Most everything we now associate with national parks was first developed there, so for many people Yellowstone is what comes to mind when they think of a national park. That’s surely why Hanna-Barbera set their Yogi Bear cartoons in “Jellystone” Park.
Yellowstone’s 8,987 square kilometers offer a rich collection of forests, rivers, 290 waterfalls, and abundant wildlife. But the park is most famous for a unique assortment of over 10,000 geothermal features, many of them in landscapes right out of science fiction. (Yellowstone’s wildlife includes some 150 grizzly bears, an endangered species. If you happen to see the real-life Yogi or Boo-Boo, the Park Service strongly recommends staying 100 meters away. People regularly get injured in “bear encounters.”)
Yellowstone’s location in western Wyoming (with small sections spilling over into Montana and Idaho) makes it— along with its smaller, less ostentatious southern neighbor, Grand Teton National Park— the quintessential summer road trip destination for over two million visitors each year. Families from around the country can escape urban traffic jams to view the wonders of nature through the windows of their minivans and SUVs, while jammed bumper to bumper with all the other families’ minivans and SUVs. Unfortunately, congestion is now a major part of the “experience” when visiting any of the popular national parks in the summer.
Both the park and the Yellowstone River that begins within its boundaries got their names from the colorful Grand Canyon of the Yellowstone. Like the famous Grand Canyon in Arizona, it’s the result of a river slowly but inexorably cutting through layers of rock over millions of years. Before that, percolating mineral-rich water, heated to boiling by volcanic activity in a former geyser basin, permeated the rock layers with yellow iron compounds. The canyon is 275 meters deep in some places, and 800 meters wide.
The 18th century French fur trappers who “discovered” the river and canyon named it with a French translation of Mi-Tsi-A-Da-Zi, which they believed to be the local Hidatsa (also called Minnetaree) Indian name for the river. They called it Roches Jaunes, which means “Yellow Rocks.” That was later rendered into English as Yellowstone, presumably because it sounds better. But historians now believe that Mi-Tsi-A-Da-Zi actually referred to yellow sandstone bluffs along the river near Billings, Montana.
I visited Yellowstone in late May, which many guidebook authors consider one of the best times to go there. The summer crowds and traffic jams haven’t yet arrived, and there’s a decent chance of pleasant weather. Snow (usually) has given way to emerging greenery, rivers and waterfalls at their peak size and flow, and scenic seasonal lakes that exist only briefly after the snow melts.
The park’s roads are closed from the beginning of November through the end of April. Hardy adventurers can brave the cold snowy winter on snowmobiles, cross-country skis, or snowcoach tours in specially modified vans. Between April and June, the Park Service plows the winter’s snow from the roads and prepares them for opening. The date each road opens varies unpredictably each year, as winter-like conditions can last through June.
The freedom from crowds and traffic jams carries the tradeoff of unpredictable weather that can make an off-season visit risky. Had I arrived a week earlier, most of the park would have been inaccessible. Although all the roads were open throughout my visit, snow was still on the ground in many places. The sky was also overcast enough of the time to make photography challenging. A bright white or elephant-gray sky does not provide the ideal background for the plume of an erupting geyser.
Yellowstone sits above what was the largest volcano in North America. An enormous eruption some 640,000 years ago— possibly 1,000 times larger than the one at Mount St. Helens in 1980— created a giant caldera, a collapsed depression 85 kilometers long and 45 kilometers wide. Subsequent smaller eruptions, the most recent of which was about 70,000 years ago, filled in the caldera.
Although another cataclysmic eruption doesn’t seem imminent, the “hot spot” deep in the Earth’s mantle still generates enough volcanic activity to heat rain and melted snow that collects underground to boiling temperatures. As it bubbles, seeps, or explodes to the surface, this hot water creates the diverse collection of pools, mud pots, fumaroles, and geysers for which Yellowstone is renowned. Shifting magma also produces thousands of earthquakes each year, most of which are felt only by seismographs.
Geysers are the most flamboyant of Yellowstone’s geothermal features. The largest ones can shoot a jet of boiling water tens of meters into the air. Old Faithful is the park’s (and the world’s) most famous geyser. Though it’s neither the largest, the most active, nor the most explosive of Yellowstone’s geysers, its predictable eruptions hurl as much as 32,000 liters of water and steam up to 56 meters high.
The popular but erroneous myth that Old Faithful erupts on the hour may have originated early in the 20th century, when the average time between eruptions was close to an hour. That interval has lengthened over the years to around 90 minutes, and follows a consistent pattern that depends on the length of the previous eruption. After a “short” eruption (less than 2.5 minutes), Old Faithful will next erupt 65 minutes later. After a “long” eruption (more than 2.5 minutes), the next eruption will occur in 91 minutes. That relationship allows park rangers to tell visitors the time of the next eruption, plus or minus ten minutes. The overall average is 90 minutes because “long” eruptions have become much more common than “short” ones.
Yellowstone’s colorful pools have quieter personalities. They collect near-boiling water that lacks sufficient pressure to erupt as geysers. They also collect thermophilic (Greek for “heat-loving”) microbes that can thrive in water so hot and sulfurous that it would quickly kill other organisms. The species that enjoy the hottest temperatures bask inside the pools, painting them dark blue, green, or yellow. Others grow in bright orange mats along the cooler edges of a pool. Wooden boardwalks along the pools prevent visitors from ruining the fragile ecosystem. The boardwalks also prevent the scalding water from ruining fragile visitors.
Pools come in sizes to fit every taste. Grand Prismatic Spring is the largest, 90 meters across and 50 meters deep. The intensely blue pool is surrounded by a large vividly-colored mat of thermophilic microbes. Opalescent Pool is the runoff from a geyser that began erupting in the 1950s. As the collected water is much cooler than a typical hot water pool, it’s really more like a pond. After the water inundated and killed a stand of lodgepole pines, dissolved minerals deposited a crust of white silica on the bottom of the dead trees and stumps.
I don’t know which pool is the smallest, but many petite pools are actually geysers that aren’t currently erupting. A geyser can become a non-erupting pool (or vice versa) when changes to the underground “plumbing” alter its water supply. Earthquakes are the most common cause; but construction, park improvements, or other human activities can also derange the “plumbing.”
Whatever the cause, such changes frequently (and sometimes abruptly) alter the color, eruption pattern, or other characteristics of geothermal features. That’s why some of Yellowstone’s features have puzzling names, describing what they were like decades ago. But it’s surely more practical to leave historical names in place than to continually rename features as they evolve. In time, the Old Faithful geyser (discovered and named in 1870) may lose its predictability and even go extinct. Future visitors will then wonder why a nondescript mound that perhaps occasionally emits wisps of steam is called “Old Faithful.”
The Mammoth Hot Springs section of Yellowstone is an almost surreal landscape that invokes a science fiction movie set. Appropriately, it’s the result of an ongoing chemistry experiment in which nature is the mad scientist.
The hot water under Mammoth Hot Springs percolates through an accumulation of porous limestone that was once the bottom of an ancient sea. Rather than collecting in pools or building up pressure to make geysers, the water slowly seeps and bubbles to the surface as “springs.” As it makes its underground journey, the water mixes with volcanic carbon dioxide gas to create a carbonic acid solution much like club soda. This acidic seltzer dissolves the alkaline limestone. When the carbonated water reaches the surface, the carbon dioxide bubbles away into the air. Without the carbonic acid the “flat” water can no longer dissolve the limestone, which then precipitates as a deposit of travertine.
Travertine is calcium carbonate, the protean ingredient of limestone, eggshells, Tums, pearls, and marble. It creates large formations through accumulated precipitation and evaporation, in a process similar to the development of stalagmites in caves or the tufa formations at Mono Lake in California. Although the travertine is gleaming white when it’s first deposited, bacteria and algae soon colonize it where the water flows, painting the travertine pink, orange, and brown.
A spring can sculpt eerie “melted” formations as the travertine dissolves in new hot water, channeling the spring’s flow in new directions. Palette Spring resembles dripping paint on an artist’s palette. Cupid Spring looks like the melted residue of candles. Sometimes the buildup completely clogs the outlet, drying up the spring and killing its colorful microbial population. The Devil’s Thumb, part of the Palette Spring formation, is a ghostly-gray extinct spring.
The calcium-laden water may also form terraces. As the water collects in pools and then overflows, the travertine deposit creates a kind of “stone waterfall” that drains into a new pool. As the pools collect and overflow, they add travertine tiers to the terrace formation.
A trail circles Minerva Terrace, the largest and most ornate of the terraced travertine formations. A menagerie of thermophilic organisms paint the terraces in shades of pink, brown, and orange. Standing at the bottom of Minerva Terrace on a day when a blue sky is decorated with puffy white clouds, it’s easy to imagine an elaborate stairway ascending into the heavens.