Yellowstone: America's First National Park and Its Geothermal Wonders

Yellowstone National Park, established in 1872 as the world's first national park, covers 8,983 square kilometres of the Rocky Mountains in Wyoming, Montana, and Idaho. The park sits atop the Yellowstone Caldera, a supervolcano that last erupted 640,000 years ago in an explosion 1,000 times more powerful than the 1980 eruption of Mount St. Helens. The caldera is still active — the ground in parts of the park rises and falls by centimetres each year as magma moves beneath the surface — and the geothermal features that make Yellowstone unique are a direct expression of this volcanic energy.

Old Faithful, the park's most famous geyser, erupts approximately every 90 minutes, sending a column of boiling water and steam between 30 and 55 metres into the air for one to five minutes. The geyser has been erupting with this regularity since at least 1870, when the first scientific expedition to the area recorded its behaviour, and the predictability of its eruptions — rangers can predict the next eruption to within ten minutes — has made it the most visited geyser in the world. The Upper Geyser Basin surrounding Old Faithful contains the highest concentration of geysers on Earth, with over 150 geysers in an area of just a few square kilometres.

The Grand Prismatic Spring, in the Midway Geyser Basin, is the largest hot spring in the United States and the third largest in the world, measuring 91 metres in diameter and reaching a depth of 49 metres. Its extraordinary colours — deep blue at the centre, where the water is too hot for microbial life, shading through green, yellow, and orange to a vivid red at the edges, where heat-loving bacteria called thermophiles form dense mats — are best seen from the overlook trail on the hillside above the spring, where the full circular pattern is visible.

The Lamar Valley, in the northeastern corner of the park, is known as the Serengeti of North America for the density and diversity of its wildlife. Bison herds of several hundred animals graze the valley floor; pronghorn antelope sprint across the sagebrush flats; grizzly bears dig for roots and ground squirrels on the hillsides; and the wolves reintroduced to Yellowstone in 1995 — after a 70-year absence — hunt the elk and bison in packs that have become the subject of some of the most detailed wildlife research ever conducted.

The reintroduction of wolves to Yellowstone has had effects that ecologists describe as a trophic cascade — a chain of ecological changes triggered by the return of a top predator. The wolves reduced the elk population and changed their grazing behaviour, allowing willows and aspens to regenerate along the riverbanks; the regenerating vegetation stabilised the riverbanks and changed the course of the rivers; the beavers returned to build dams in the new willow thickets; and the dams created wetland habitats that supported new populations of fish, birds, and amphibians. The Yellowstone wolf reintroduction has become the most cited example of how the restoration of a single species can transform an entire ecosystem.

The Grand Canyon of the Yellowstone, carved by the Yellowstone River through the volcanic rock of the caldera, is 32 kilometres long and up to 370 metres deep, with walls of yellow, orange, and red rhyolite that give the park its name. The Lower Falls, at 94 metres, are nearly twice the height of Niagara Falls, and the view from Artist Point on the canyon rim — with the falls in the distance and the coloured canyon walls dropping away on both sides — is one of the most dramatic in the American West.

The best time to visit Yellowstone is from late May to early October, when the roads are open and the wildlife is most active. The summer months of July and August are the most crowded, with over four million visitors a year competing for parking at the major attractions. The shoulder months of May-June and September-October offer smaller crowds, better wildlife viewing (the wolves and bears are more active in cooler weather), and the possibility of seeing the park in snow — which transforms the geothermal features into something even more otherworldly, with steam rising from the hot springs against a white landscape.