Grand Prismatic Spring, Wyoming, United States

Yellowstone is the first and oldest national park in the world. It was created in 1872 and is located on a volcanic plateau that sits astride Montana, Idaho and Wyoming. Whilst the United States were conquering the “American Old West “ and slaughtering the last bison, some people had inkling that nature needed to be protected. The park is 9.000 km2 long and has the largest concentration of geothermal sites on Earth. It has more than 300 geysers, fumaroles hot springs. The Grand Prismatic Spring is 112 m in diameter. It is the park’s largest thermal basin and the third largest in the world (in size). The spectrum of colors which gave Yellowstone its name is due to the depth of the water and to the presence of microscopic algae on the edge of the bowl. Their growth in the hot water varies according to the temperature. Yellowstone has been a biosphere reserve since 1976 and was listed as a UNESCO World Heritage Site in 1978. It draws 3 million visitors a year. The five most visited natural sites in the world are on the North American continent. It drew over 98 million tourists in 2010 which is almost 10% of the 940 million international tourists counted that year. This grants it a share of about 15% of the world’s tourism revenue. On an international scale, tourism represents an amount of approximately 6.000 billion dollars that is more than 9% of the international GDP. Although it generates over 250 million jobs, tourism still has a negative impact over the environment, natural resources and local cultures.