Death Valley's 'sailing stones' drag themselves across the desert — filmed only since 2014

For decades, visitors to Racetrack Playa found heavy rocks that had seemingly crawled across the dry lakebed on their own, leaving long trails behind them. In 2014, researchers fitted rocks with GPS trackers and finally caught the mechanism: a thin sheet of ice forms after rare rain, and as it breaks up in a light wind, floating ice panels gently shove the rocks across the mud.

— Richard Norris et al., Scripps Institution of Oceanography, Racetrack Playa — PLOS ONE, 2014