Yellowstone is the first, oldest, and perhaps most famous national park. Originally designated in 1872, this 2.2-million acre park hosts more than 3 million visitors annually. Yellowstone contains about 10,000 hot springs and geysers, most of the world's total. Aside from the geothermal features, Yellowstone is also the center of the Greater Yellowstone Ecosystem, an area that supports a large variety of wildlife, including grizzly bear, wolf, bison, and elk. The National Park Service's official website for Yellowstone is http://www.nps.gov/yell.

A shaded-relief map of Yellowstone (large!).
(Source: The Total Yellowstone Page)

Bison and elk grazing near Yellowstone's West Enterance.

The Norris Geyser Basin.

Geothermal activity is the result of groundwater being heated by molten rock beneath the earth's surface. This hot, molten rock lies only a few miles beneath Yellowstone's surface, creating thousands of geothermal features. These features can be generally referred to as hot springs, but they take on several different forms. Hot springs are usually ponds of hot water that are famous for their coloration. The colors depend on the water's temperature, mineral content, algae, and how the water reflects/absorbs light. Hot springs can be flowing (like Mammoth Hot Springs) or stand as still pools. Mud pots are a type of hot spring where the water has mixed with clay and other dissolved matter, creating a sometimes colorful but sometimes muddy-looking think bubbling pond. Geysers are some of the most spectacular geothermal features because they release their water under pressure. This pressure causes a column of water to erupt into the air, sometimes hundreds of feet. Old Faithful is probably the most famous Yellowstone geyser because of its predictability. (Source: Yellowstone Media Group)

The boardwalks (left) take you near and sometimes over the thermal features in Yellowstone's geyser basins.

Steamboat Geyser, the world's largest geyser. Its eruptions are very infrequent and unpredictable.

Elk resting and grazing outside our cabins at Mammoth Hot Springs.

At the root of all this geothermal activity lies a supervolcano. Yellowstone is simply the biggest ticking bomb on the planet. It last erupted around 650,000 years ago, with other eruptions estimated at 1.3 million years ago and 2.1 million years ago. These eruptions were large enough to have a climatic effect on a global scale. Layers of the ash deposit from the last eruption have been found as far away as Iowa and California. The caldera left by these eruptions encompasses nearly two-thirds of Yellowstone National Park, and geologic evidence suggests that the pressure under Yellowstone continues to rise, indicating the direct possibility of a future eruption. (Source: Yellowstone Media Group)

Mammoth Hot Springs is known for its colorful features.

At dusk the colors turn to gray and some of the landforms look somewhat spooky.

The Hot Springs giving off steam into the cool air.

Due to the south entrance from the Tetons being closed, we changed our plans and entered Yellowstone National Park through the west entrance. By this time it was getting late in the afternoon, and we were greeted by large herds of bison and elk. If it's spring and you're a hungry large mammal in Yellowstone, along the road nearest the west entrance must be the place to be. Our first major stop was the Norris Geyser Basin. You get the feeling that the Norris Geyser Basin is generally passed over by tourists in a hurry to get to the Upper Geyser Basin and Old Faithful, but it is quite spectacular in its own right. After walking the boardwalks at the Norris Geyser Basin, we turned north to Mammoth Hot Springs, where we had reserved cabins for the night. One of the nicest things about being at Mammoth, and Yellowstone in general, was that there were far fewer people than during peak season. A few elk had wandered down to the cabins during the day, and as evening came they moved up into the hills. With the night to ourselves, we wondered around the hot springs, whose colors diminished with the sunlight.

The Grand Canyon of the Yellowstone and Lower Falls, creating one of the most dramatic views in the park.

Lower Falls framed by the trees.

Lower Falls with snow still covering the bottom of the canyon.

The next day at Yellowstone was a full one. We proceeded south again, towards the Norris Geyser Basin. We stopped and explored Obsidian Cliff, an outcropping of black volcanic glass. At the geyser basin we turned east and headed for the Grand Canyon of the Yellowstone, where we stopped for a while to admire Lower Falls. From Lower Falls we proceeded south towards Yellowstone Lake, which will still almost entirely covered with ice. Our main stop for the day was the Upper Geyser Basin, home of Old Faithful and the Old Faithful Lodge. There we had plenty of time to eat, admire the lodge, walk around the basin, and wait for Old Faithful. After Old Faithful we headed out the newly-opened south entrance, past the Tetons, and to Jackson for the night.

Heart Spring, one of the many thermal features in the Upper Geyser Basin.

The Firehole River interacts with the Upper Geyser Basin.

The dramatic colors in the thermal pools are the result several factors, including water temperature, mineral content, and algae.