What Really Drives Death Valley’s Roving Rocks?

By on March 18, 2014

The moving, sailing and sliding rocks of Racetrack Playa, Death Valley National Park in California have garnered the attention of many scientists and visitors throughout the years. The Racetrack Playa is a dry lake featuring the race track imprints of the moving rocks. The moving rocks are a geological phenomenon where the rocks, some weighing about 318 kgs, move without any human intervention.

roving-rock

Photograph by Pete Ryan

There have been many theories regarding the motion of these rocks. Research on this phenomenon started as early as 1915 when theories suggested that the wind had a role to play in moving the rocks. However, with some stones weighing 318 kgs, it is not probable for the wind to move them. Therefore this theory was discarded. In 1955, George Stanley, a geologist did extensive research on the phenomenon and stated the theory that ice sheets around the rocks help to catch the wind, initiating the movement. His theory again stressed that wind plays a role in the rocks’ movement.

Credit: Maggie McAdam

Further research was done in the 1970s by Bob Sharp and Dwight Carey where they monitored the rock movement by naming the rocks and keeping a record of their changing positions over a period of seven months.

The research continued in the 1990s by the research students of Hampshire College and the University of Massachusetts Amherst. The movement of the stones was evident to be the result of two factors: wind and ice floes. In 1996 it was discovered that the wind blowing on the Playa could be intensified and compressed due to its smooth surface and the wind gusts initiate the movement while the moment keeps them moving.

Ice and Wind

In 2006, Ralph Lorenz, a NASA Scientist, investigating the weather conditions on other planets started researching on the moving rocks. Lorenz compared the meteorological conditions of the Racetrack Playa, Death Valley to those near Ontario Laucus, a vast hydrocarbon lake on Titan, a moon of Saturn.

Lorenz conducted a simple experiment where he placed a small rock in a Tupperware filled with water so that there was an inch of water with a bit of the rock sticking out. Next, he froze the Tupperware so that there was a small slab of ice with a rock embedded in it. He then placed the ice bound rock in a container of water with sand at he bottom. In order to move the rock across the water, he just gently blew on the rock and it slid. As the rock moved, it imprinted a track in the sand.

Ralph Lorenz’s home experiment

Ralph Lorenz’s home experiment

Research in 2011 established that the existence of many of the rock-carved trails at Racetrack Playa in Death Valley National Park is predominantly due to the effect of arbitrarily weak winds on rocks that are floated off the soft bed by small rafts of ice, the ‘ice raft theory’.

Credit: Anatoliy Lukich

Credit: Anatoliy Lukich

These ice cakes need not have a particularly large surface area if the ice is adequately thick-the ice cakes allow the rocks to move by buoyantly reducing the reaction and friction forces at the bed, not by increasing the wind drag. The parameter space of ice thickness and extent versus rock size for flotation is calculated and found to be reasonable. Lorenz’s experiment illustrated this ‘ice raft theory’. Therefore, wind and ice were both the favoring theories responsible for the phenomenon.

Zainab Khawaja

F. Scott fan. Dreamer, planner, believer