Yellowstone

Yellowstone is a national park in the western United States. It covers parts of three states: Wyoming, Montana, and Idaho. The park is about 3,500 square miles. That makes it a little bigger than the state of Delaware. Yellowstone became the world's first national park in 1872, when President Ulysses S. Grant signed a law protecting it.

The park sits on top of one of the biggest volcanoes on Earth. This volcano is called the Yellowstone Caldera, and it is a "supervolcano." A supervolcano is a volcano that can have eruptions hundreds of times bigger than a normal one. Yellowstone has had three huge eruptions in the last 2.1 million years. The last one was about 640,000 years ago, long before humans lived in North America. The volcano is still active today, but scientists do not think it will erupt anytime soon.

Because of the volcano, hot melted rock called magma sits just a few miles below the surface. That heat creates geysers, hot springs, and bubbling mud pots all over the park. Yellowstone has more than 10,000 of these hot features. That is about half of all the hot features on Earth, in one park.

The most famous geyser is Old Faithful. A geyser is a hot spring that shoots water high into the air. Old Faithful got its name because it erupts on a regular schedule, about every 90 minutes. It blasts boiling water up to 180 feet in the air. That is taller than a 15-story building.

Yellowstone is also home to huge numbers of wild animals. About 5,000 bison live in the park. This is the largest wild herd in the United States. Elk, moose, black bears, grizzly bears, bald eagles, and coyotes all live there too. Gray wolves were wiped out of Yellowstone by hunters in the 1920s. In 1995, scientists brought wolves back. The return of the wolves changed the whole park. Elk herds spread out more, young trees grew back along the rivers, and beavers came back to build dams.

One of the park's most beautiful spots is the Grand Canyon of the Yellowstone. This is a deep canyon carved by the Yellowstone River. It has two big waterfalls, bright yellow cliffs, and drops of over 1,000 feet. Those yellow rocks may be where the park got its name.

About four million people visit Yellowstone every year. They come to watch geysers erupt, spot bison crossing the road, and hike through forests and meadows. Yellowstone showed the world a new idea: that wild places can belong to everyone and be saved for the future.