On September 18, 1938, an inexplicable onset of darkness during the day was recorded on the Yamal Peninsula. Soviet geologists working on the Yamal Peninsula became unwitting witnesses to a true "black day" in the history of the region. A band of complete darkness, approximately two hundred to two hundred fifty meters wide, descended upon the land; this dark zone also moved from west to east and soon engulfed the Ob Bay. Suddenly, it became as dark as night in the middle of the day. Geologists who witnessed this phenomenon described it as an abrupt darkness accompanied by radio silence. After launching several signal flares, they saw that very dense clouds hung close to the ground, blocking sunlight. The eclipse lasted for about an hour, after which the darkness dissipated on its own. Scientists have yet to explain the nature of this mysterious phenomenon.