Can a heavy stone move by itself, without help from a person? The answer is yes! It looks like magic, but it isn't. And it only happens on the floor of a playa.
A playa is an area of dry, flat land. When it rains, water goes into the playa floor. At night, it gets cold. The top of the water becomes a thin sheet of ice. The ice sheet rests above the water. In the morning, the sun comes out. The ice begins to break. When it breaks, it pushes the stones on the playa floor. They can move five meters in one minute! That means their speed is 0.3 kilometers an hour.
For many years, nobody knew how the stones moved. But in 2014 some people studied the stones carefully. They did their study in Death Valley National Park, California. They used GPS and made a long video of the stones.
旱湖湖床指的是一塊乾燥平坦的地域。下雨的時候雨水會滲入湖床，入夜後天氣轉冷，表層的水面就會結成一片薄冰，浮在水的上方。到了早上，太陽升起，薄冰開始裂開，此時就會推動湖床上的石塊。這些石塊一分鐘可以移動五公尺遠！這相當於時速 0.3 公里。
多年來沒有人知道石塊如何移動，直到 2014 年，有人仔細研究這些石塊，他們在加州的死亡谷國家公園進行研究，以衛星導航系統，針對此類石塊長時間拍攝追蹤影片。