Yellowstone National Park, established in 1872, was the first national park to be formed in the US and probably in the world as a whole. It spans an area of almost 9,000 square kilometres comprising lakes, canyons, rivers and mountain ranges. The Park is centred over the Yellowstone Caldera, the largest supervolcano on the American continent. The caldera is a dormant volcano that has erupted forcefully several times in the last two million years. Well over half of the world's geysers and hydrothermal features are in Yellowstone - this gallery showcases just a very small number of them but includes many of the major and better-known examples.