In what year was the Darvaza gas crater ignited by geologists and has been burning continuously since?

The Darvaza gas crater, known locally as the "Door to Hell" or ''Gates of Hell", is a natural gas field in Derweze, Turkmenistan, that collapsed into an underground cavern in 1971, becoming a natural gas crater.

The site was identified by Soviet engineers in 1971. It was originally thought to be a substantial oil field site. The engineers set up a drilling rig and operations to assess the quantity of oil available at the site. Soon after the preliminary survey found a natural gas pocket, the ground beneath the drilling rig and camp collapsed into a wide crater and was buried.

Expecting dangerous releases of poisonous gases from the cavern into nearby towns, the engineers thought it best to burn the gas off. It was estimated that the gas would burn out within a few weeks, but it has instead continued to burn for more than four decades.

The crater is a popular tourist attraction. Since 2009, 50,000 tourists have visited the site. The gas crater has a total area of 5,350 m2, the size of an American football field. The surrounding area is also popular for wild desert camping.