Volcanic region, southwestern Alaska, U.S. Located in Katmai National Park , the valley covers 56 sq mi (145 sq km).
It was created in 1912 when the eruption of the Novarupta and Mount Katmai volcanoes covered the valley in a flow of lava. When an expedition visited the site in 1915 they discovered tens of thousands of fissures known as fumaroles spouting smoke, gas, and steam in the valley floor. The largest was 150 ft (46 m) in diameter; some had temperatures as high as 1,200 °F (649 °C). About 60 years later, there were fewer than 12 fumaroles left. In the 1960s U.S. astronauts used the scarred region to train for Moon landings.