Yellowstone National Park Wy

Yellowstone Sits on Top of an Active Supervolcano and Is Open to the Public

The Yellowstone hotspot has produced eruptions for 2.1 million years. The most recent supervolcanic eruption (640,000 years ago) covered most of North America in ash. The caldera from that event is the entire central valley of the park. All the geothermal activity – geysers, hot springs, fumaroles, mud pots – is powered by this same geology. This is not a constructed attraction; it is an active volcanic system that happens to be the world’s first national park (established 1872).

The Geothermal Features

Old Faithful erupts approximately every 90 minutes (the rangers post predicted next eruption times accurate within about 10 minutes). On summer days the boardwalk area holds several thousand people; visit at the first eruption of the morning or the last of the evening.

Grand Prismatic Spring is the largest hot spring in the United States: 91 metres wide, 49 metres deep. The rainbow colouration (deep blue centre, progressing through green, yellow, and orange to brown at the edges) comes from pigmented bacteria living at different temperatures. The bacteria survive in water up to 87 degrees Celsius. The best view is from the Fairy Falls Trail overlook, about 1.5 kilometres from the Midway Geyser Basin car park – from the boardwalk at the spring itself you cannot see the full ring of colour.

Mammoth Hot Springs is a different geology: calcium carbonate terraces built by flowing thermal water. The travertine terraces grow and change; areas active a decade ago may now be dry.

Wildlife

The Lamar Valley in the northeast is the best wildlife viewing area and the best place in the continental United States to watch wolves in the wild. The 1995 wolf reintroduction brought grey wolves back after a 70-year absence. The valley also has large bison herds, grizzly bears (particularly visible in spring), pronghorn, and coyotes. Dawn and dusk are the productive hours. Binoculars are essential.

The rules are not decorative: stay at least 100 yards from bears and wolves, 25 yards from bison. Bison look slow; they can run at 35 miles per hour and cause more injuries per year in Yellowstone than bears. Never approach them.

Staying and Getting Around

Old Faithful Inn (a 1904 log structure, the largest log building in the world) is architecturally significant and worth staying in for the location. Book months ahead through Xanterra. Campgrounds fill by 8am in summer. September is arguably the best month: crowds drop after Labor Day, the elk rut begins (dramatic and audible), and the light is excellent.

A rental car is mandatory; the park has no ride-share service. The Grand Loop Road is 143 miles; two to three days minimum allows proper coverage.