Racetrack Playa: Turtles Race Faster Than These Famed Stones!

From a far glance, the flat, dry surface of Racetrack Playa, in Death Valley, California, invites you to perceive a cloudy lake. Nearing the Playa, this mirage evolves into a reality of silt and clay where nothing seems possible. Here, the lake bed serves as a respite to the surrounding mountains as it waits eagerly for the meager annual rainfall of 3 inches. With the help of this water, the surface changes from dry silt to wet mud, offering us an incredible mystery from a muddy mess.

These rocks and their trails are sprinkled throughout Racetrack Playa, proving seemingly impossible movement. Wakes of thirsty ground, frozen in time, linger behind them, showcasing their lively sailing trips across the dry lake bed underneath.

Explaining the Sailing Stones

Scientists have struggled to explain the movement of these stones for decades. Until recently, there were only two main theories explaining the movement: hurricane force winds, or thick ice. Both theories accounted for wind, rain and ice but required these conditions to create a Samsonite feat of natural strength to move the rocks. Thanks to new technology, scientists have finally been able to get some answers.

Slow and Steady

In 2011, a team from Scripps Institution of Oceanography set a weather station in the Playa and placed GPS tracking devices on the stones. They expected it to take years to get the right coincidence of unknown factors, but as luck would have it, just two years later they saw – and measured – the rocks moving!

Following a cold December night, the team traveled to the site. A thin, frozen pond had trapped the stones overnight due to an unusually high amount of snow. A light breeze was noticed in the mid-morning but didn’t affect the stones until the bright sun quickly began to melt the ice in the early afternoon. The melting ice began to crack and pop, forming wide and light sheets of ice. The ice, due to the force of the wind, applied buoyancy to the trapped rocks and bulldozed the rocks across the surface. This “ice sailing” process slowly moved the rocks and created the mysterious trails.

As for racing on the playa, these stones are not breaking any speed barriers. Recordings showed winds at maximum speeds of only 10 mph, and ice less than ¼ of an inch thick. These conditions, combined with ice melt from a bright sun, were able to move rocks ranging from 18 to 37 pounds about 6 to 20 feet per minute (0.07 – 0.23 mph). To put this in perspective, the average turtle, who travels at a speed of 264 feet per minute (3 mph), is almost 13 times faster than the sliding stones! Even more so, the rare factors and slow speed of the process have only moved the rocks for a total of a few minutes in the past decade!