A desert mystery

Saturday, Nov. 11, 2000 | 10:34 a.m.

On the web

A map of rock positions and trails as of 1996 can be found on the website geosun.sjsu.edu/paula/rtp

If the sliding stones at Racetrack Playa in Death Valley, Calif., could talk, they would probably have a few good stories to tell.

In the past 50 years the moving stones have seen their share of mysterious behavior from scientists, hobbyists, professors and UFO-ologists.

Research teams and college study groups have measured, weighed, discussed and posed with the rocks that slide across a dry lake bed, leaving perfect trails a half-inch deep and hundreds of feet long.

In the 1950s the complacent stones watched a researcher saturate an area of the lake bed, then use a plane's propellers to try to move the rocks, hoping to prove that gusts of wind moved them during rains.

Years later another researcher temporarily penned some of the rocks to disprove a theory that ice sheets were pushing the stones along.

Some say wind gusts are blowing the rocks -- weighing up to 700 pounds -- at 3 to 4 mph, slightly uphill, when the lake bed is slick during rains. Other speculators suggest the rocks are moving from magnetic causes, vibrations from earthquakes or dust devils -- small whirlwinds that scoot them along.

Out of sight

Despite all the theories, no one has come up with evidence of what moves the rocks. Because of stormy conditions that are thought to move the rocks, nobody has actually seen the rocks move. Circular, straight, hairpin or zig-zag trails left behind are the only evidence.

"I thought I could just walk out there and figure it out," said Carl Long, a member of a Southern Nevada Mensa group that studies the rocks. "But you don't just figure it out. The more you look, the more complicated it gets."

Mensa members travel the 27-mile, sometimes washed-out dirt road annually at Halloween to study the stones.

Although it doesn't take itself "terribly seriously," the group has come up with its own theory -- one that is in contrast with the two most predominant theories. (One of those theories holds that ice sheets floating on water move the rocks, the other that wind alone pushes the rocks across the lake beds during rain.)

A year ago Long noticed that cracks in the tiles near the rocks were deeper than cracks surrounding tiles on the rest of the lake bed.

After exploring the idea further, the group suggests that during storms the rocks block the wind, causing more water to fall near the rock. As the lake bed dries, the rock provides shade, causing the ground beneath to remain saturated for a longer period of time, causing the ground to swell and form a small hill.

During the following rainstorm, water falling into the shallower cracks flows into deeper cracks, Mensa member Terry Moran said. "This continues for a number of rains. The ground under the rock swells. Now you've got a 7-inch hill."

Moran and Long said the hill is essential to their theory. They believe that in a storm the slope of the hill, combined with the wind gusts and a slick lake bed, enable the rocks to move.

"What we need is to be there right after a rainstorm," Moran said. "That's when you really see things in action."

Another theory

Paula Messina, an assistant professor of geology at San Jose State University, said the idea of a small hill forming below the rocks is possible, but supports the idea that wind gusts alone can scoot the rocks across a slick clay surface. With a friction level reduced to zero, even a finger could push nearly a 1,000-pound rock, Messina said.

But in 1995 John Reid, a professor at Hampshire College in Massachussetts, brought in a team that weighed and measured the rocks and pushed them after saturating the area. He said that winds at least 500 mph (never recorded on Earth; hurricane force begins at 74 mph) would be needed to move even the smaller stones.

Reid supports the idea that ice sheets move the rocks, an idea not supported by Messina, who says ice sheets, floating on a layer of water and moving the rocks collectively, would create parallel trails. The trails may have similar signatures, she said, but "they are really erratic."

The stones were the subject of Messina's doctoral dissertation and are mentioned in her Geomorphology class. In 1996 she used the Global Positioning System to map each of the complacent stones, none of which has moved since 1997, she said.

Evidence of splash marks, "as if the rocks are barreling through" the lake bed, also argues against the theory of ice sheets, Messina said.

As with splash marks, the Mensa special interest group is convinced there wouldn't be berms outlining the trails if ice sheets were a factor. But the group agrees with Reid, that wind alone wouldn't push the rocks.

"The only way you could get enough wind pressure (to move the rocks) would be some sort of dust devil," Moran said. "I've never seen a dust devil pick up a 700-pound stone and move it."

Wind gusts powerful enough to blow away a 700-pound rock would also blow away the berms lining the tracks, Moran said. Ice sheets would flatten or melt the berms, he said.

Although he plans to write a scientific monograph to "throw the theory into the ring," he's not so sure a theory hypothesized by amateurs will be well received in the science community. He has already created a video documenting the theory.

Changes

Unfortunately recent flooding had washed away some of the trails and caused clay and other residue to fill the cracks between the tiles, making it difficult for the group to test its theories. Moran, however, says he will be returning to the playa (dry lake bed) in March to take measurements.

Manning the remote area to personally monitor the stones during a storm isn't a likely option for Moran and others who study the phenomenon.

"If a 700-pound boulder is moving, you're not going to be staying put either," said Messina, who travels to the playa twice a year.

Because the playa is in a national park and a protected wilderness area, radio collars, cameras and other equipment can't be used to monitor the rocks either, she said.

Messina, who has already blown 13 tires on the gravel road, says she'll continue to study the stones. She's written several pieces on the stones that she first saw when hiking Death Valley.

"It didn't take long before I realized that I wanted to study the stones professionally," she said. "There is nothing like this. It's counter-intuitive. You go out there and see this giant boulder and it has a footprint."