Mystery solved: What makes the sliding rocks of Death Valley move on their own (Image source: Wikipedia)

In one of the hottest and driest parts of the world, there is a phenomenon that is most unexpected. At a remote dry lake bed in the world-famous Death Valley area in the United States, large rocks are seen to be in motion. They slowly slide over the desert floor, with long tracks that do not seem to ever lift. The incredible movement of these rocks in the Racetrack Playa area has been a phenomenon not understood by scientists as well as tourists. There was never any animal or wind activity that could have caused the movement of the large rocks over the desert surface. Over the years, several theories were put forward, perhaps wind or even magnetic activity. Recent studies and research in the area made the phenomenon seem like one of the most interesting slow-motion events in nature.

What are the sliding rocks of Racetrack Playa

Racetrack Playa, in a remote part of Death Valley, is a dry lakebed that turns a shallow, slick surface after the occasional rain. The stones scattered across the dry lake, also known as “sailing stones” or “sliding rocks,” leave behind long trails etched into the soft mud as if they had been propelled by an invisible force. These trails can extend for tens of meters, often hundreds of meters, sometimes in straight lines or gentle curves, but for decades, nobody has watched them in motion.

How scientists finally observed the rocks move

In 2013 and 2014, a team led by researchers set up on Racetrack Playa GPS-equipped stones, weather stations, and time-lapse cameras. For the first time, they documented rocks actually moving, in the process leaving trails behind. Their 2014 paper, “Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion”, chronicled for the first time the resolution of the long-standing mystery. The movement associated itself with shallow pools of water, forming after rain; freezing temperatures at night; and thin sheets of ice, which form on the playa surface.

The ice, sun, and wind mechanism

So how do massive rocks slide across a nearly flat desert floor? The answer is a precise combination of conditions:

This movement continues until the ice disintegrates or the water evaporates, leaving behind the characteristic trails in the mud.

Why this rare phenomenon only happen occasionally

Sliding stones don’t move every year, only when the rare mix of conditions is just right. Death Valley is one of the driest places in North America, so it needs enough rain to create shallow water, temperatures cold enough to freeze that water at night and sunshine to break the ice in the morning. Since all three factors have to line up, events of rock movement can only occur a few times in a decade.

What the trails reveal

When these boulders move, they leave behind peculiar trails that tell their tale. Some of these trails are straight, some bend gradually, and others intersect each other. The length and direction of these trails would depend on wind direction, patterns of ice breakup, and the duration the ice sheets remained intact. Over time, hundreds of these trails were mapped by scientists, but it was the recording of actual motion that confirmed the cause.

Visiting the Racetrack Playa

Nowadays, the place is considered a bucket list destination for geologists, photographers, and curious tourists. It’s most accessible in cooler months when conditions are milder, and occasionally when rare winter rain brings the sliding stones to life. If planning a visit to the place, tourists can be prepared to drive through rugged terrain.