What's the mystery behind these moving stones?

Have you ever heard of the moving rocks of Death Valley National Park? They are also referred to as the sailing stones.
Interesting Engineering

Have you ever heard of the moving rocks of Death Valley National Park? They are also referred to as the sailing stones.

It is Richard Norris, a paleobiologist at the Scripps Institution of Oceanography, and his cousin Jim Norris who were visiting the national park in December of 2013 that uncovered the mystery behind this phenomena. This all started when they arrived at the site of the rocks, just as the playa was covered with a pond of water. 

Suddenly, the rocks began moving right in front of them. The cousins observed that the rocks required a rare combination of events to begin their smooth motion. 

The playa they were in must fill up with water and be deep enough to form floating ice during cold winter nights but still shallow enough to expose the rocks. On sunny days, the ice would begin to melt and proceed to break into floating panels that pushed the rocks in front of them. 

These sliding rock tracks have been the subject of studies since the early 1900s. However, since the reasons behind the moving stones would be revealed in the 2000s, it opened the door to many hypotheses about why or how the stones moved. The first account to document the phenomenon was in 1915 by a man named Joseph Crook from Nevada, who was visiting the Racetrack Playa, named for the long trails that the rocks leave in the mud. 

Over the years, the playa also had a lot of interest from geologists. In 1948, Jim McAllister and Allen Agnew mapped the bedrock area and published a report about the sliding rocks in the  Geological Society of America Bulletin. 

Meanwhile, a national park ranger in 1952 named Louis G. Kirk recorded furrow length, width, and general course. It was around this time that speculation about how the stones moved began. 

These ideas were either very complex or involved the supernatural. In 1955, George M. Stanley published a paper on the subject. After extensive track mapping and research, he speculated that ice sheets were behind the rocks’ mysterious movement. 

Moving forward to the 1970s, Bob Sharp and Dwight Carey started a Racetrack stone monitoring program. They named and labeled 30 stones, then of which moved in the first winter. In the seven-year period of their extensive research, only two stones didn’t move. 

One of these was called Karen, a block of dolomite weighing 700 lb (320 kg). Although Karen didn’t move during the research period, it did disappear before May 1994. Fortunately, Karen was rediscovered by researcher Paula Messina in 1996.