Sailing Stones

Sailing stones or sliding stones are a strange geological Phenomenon that occurs in Racetrack Playa,in Death valley, USA.Rocks weighing more then 300 kg move accross the flat lakebed on their own, leaving tracks as long as 60m on their own surface. Nobody knows for sure how and  why they move as no one one has ever witnessed the stones in motion.
         The rocks move every 2 or 3 years and leavs   clear trails on the dry mud. Some tracks are straight while others are wondering . Two rocks may start out together on parallel  but one may abruptly change direction going right , left or even in the reverse direction . Most of these rocks last not more than seven years.
       Many theories giving possible explanations for the mystery abond, but none have been proved.