The Dyatlov Pass incident refers to an event that resulted in the deaths of nine ski hikers in the northern Ural mountains on the night of February 2, 1959. The lack of eyewitnesses and subsequent investigations into the hikers' deaths have inspired much speculation. Investigators at the time determined that the hikers tore open their tent from within, departing barefoot in heavy snow. Though the corpses showed no signs of struggle, two victims had fractured skulls, two had broken ribs, and one was missing her tongue. According to sources, four of the victims' clothing contained substantial levels of radiation. There is no mention of this in contemporary documentation; it only appears in later documents. Soviet investigators determined only that "a compelling unknown force" had caused the deaths.