Yellowstone National Park, Idaho, Montana and Wyoming, U.S.A. (August 3-5, 2008)

Spanning three states and approximately 2.2 million acres, Yellowstone NP is in a league of its own. It became the world’s first national park in 1872, and has since been named a UNESCO Biosphere Reserve and World Heritage Site.

A series of massive volcanic eruptions that took place 2 million years ago, 1.3 million years ago and 640,000 years ago shaped Yellowstone into its present form. A 30- by 45-mile caldera (a collapsed magma chamber) in the heart of the park, formed by the most recent eruption, displays the volcanic heritage – and potential – of the area: magmatic heat still powers the park’s many geysers, hot springs, fumaroles and mudpots. In fact, Yellowstone contains half of all the world’s known geothermal features, and it has the highest concentration of geysers in the world (two thirds of all those on the planet).

Aside from the hydrothermal wonderland that first drew curious visitors, Yellowstone has a diverse range of landscapes to explore, from near-desert in the north to subalpine meadows and forests in the east. Mountains surround the volcanic plateau, a deep canyon cuts through the northeast, and the Continental Divide winds its way through the southern part of the park. Today, visitors come just as much to see the abundant wildlife that roam the park, including bison, elk, grizzly and black bears, moose, big horn sheep, wolves, coyotes, deer and a host of fish and birds.

With nearly 1,000 miles of trails, it could take a lifetime to see all that Yellowstone has to offer. But armed with a good map and helpful trail guides from the many visitor centers, one can make a valiant effort to at least see the highlights.

Yellowstone’s most famous attraction: Old Faithful geyser. The people gathered to the right of the photo will give a sense of perspective. Old Faithful erupts approximately every 90 minutes, and an eruption expels 3,700-8,400 gallons of boiling water, reaching a height of 106-184 feet.

Punch Bowl Spring in the Upper Geyser Basin near Old Faithful

Excelsior Geyser at Midway Geyser Basin produces about 4,000 gallons of scalding water every minute. When this geyser erupted in 1985, it continued for two whole days!

Grand Prismatic Spring, Yellowstone’s largest hot spring, at Midway Geyser Basin. The bright colors found in and around the thermal areas are formed by heat-loving microorganisms (thermophiles) such as algae, bacteria and archaea.

Lone Star Geyser, about 3 miles south of Old Faithful. Lone Star has one of the largest cones in the park, and its eruptions occur in 3-hour cycles, with water reaching heights of 30-40 feet.

People explore the Midway Geyser Basin area along a series of boardwalks