Yellowstone National Park is the most famous national park in the United States. It is situated in northwestern Wyoming and partly in southern Montana and eastern Idaho. It was established in 1872 as the first national park of United States. With its 898 315 hectares' area is Yellowstone the largest national park of the country. It lies mostly on volcanic plateaus at 2300 to 2700 m above sea level, surrounded by Custer, Shoshone, Teton, Targhee, Beaverhead, and Gallatin national forests. It has more than 800 km of roads and more than 1600 km of trails. The John D. Rockefeller, Jr., Memorial Parkway, an 130-kilometre scenic roadway established in 1972 connects Yellowstone with Grand Teton National Park.

Yellowstone has many notable features, including rugged mountains, fossil forests, eroded lava flows, a black obsidian (volcanic-glass) mountain, and other geological formations, but biggest attractions are its 10 000 geysers, Mammoth Hot Springs, mud volcanoes, and lesser thermal phenomena. Many of the geysers erupt to heights of 30 meters or more.

Probably the most famous geyser of Yellowstone is "Old Faithful". It lies at the head of the Upper Geyser Basin in Yellowstone. It was so named in 1870 by the Washburn-Langford-Doane Expedition because it seemed to erupt "faithfully" every 65 to 70 minutes. Under a continuous observation, however it has been found that the eruptions occur quite irregularly with intervals from 33 to 148 minutes. These are understandably the extremes, on the average the Old Faithful erupts every 60 minutes. In every eruption there are about 45 000 l of hot water plus billowing steam ejected to height of about 52 m and the column stands for approximately 4 minutes. Geologists place the age of the geyser at 200-300 years.

I will explain now, what a mud volcano is. A mud volcano is a mound of mud heaved up through overlying sediments. The craters are usually shallow and may intermittently erupt mud. These eruptions continuously rebuild the cones, which are eroded relatively easily.

There are two types of mud volcanoes.

Some mud volcanoes are created by hotspring activity, where large amounts of gas and small amounts of water react chemically with surrounding rocks and form boiling mud.

Other mud volcanoes entirely of nonigneous origin occur only in oil-field regions that are relatively young and have soft, unconsolidated formations.