Search This Blog

Search This Blog

Search This Blog

Sunday, 12 January 2014

WANDERING ROCKS OF DEATH VALLEY: Stones that slide across the ground under some kind of mysterious force

WANDERING ROCKS OF DEATH VALLEY: Stones that slide across the ground under some kind of mysterious force



At Racetrack Playa in the Death Valley, California, pictured, heavy rocks appear to move across the floor while no one is looking. Scientists believe the movement may be caused by the ice stuck to the bottom of the stones, which are then moved in the wind. However, no-one has caught the stones in the act

At Racetrack Playa in the Death Valley National Park, California, strange forces are at work. Forces capable of pushing heavy rocks across the flat surface of a dried-out lake while no one is looking. Scientists have scratched their heads over the trails left by these sliding stones since early in the 20th Century. In the 1960s, Californian geologists started a rock monitoring programme. They tracked 30 stones, weighing up to 25kg, 28 of which moved during a seven-year period – some more than 200m. Analysis of the stones’ trails suggested speeds of 1m per second. In most cases, the stones travelled in winter. In the decades that followed, theories about ice and wind gained support. Others involved algal slime and seismic vibrations.

So what’s happening? Are the stones sliding around in bad weather? ‘We think so,’ says Dr Gunther Kletetschka, of the Academy of Science of the Czech Republic and Charles University in Prague, who led a 2013 study on the stones. His team’s research describes what happens when water on the Playa surface freezes. According to their theory, ice stuck to the stones remains frozen longer than the surrounding ice – because rock conducts heat away faster. This reduces the force between the rocks and the Playa surface, so they can be pushed by the wind.

No one has yet caught the stones in the act, and they’ve been strangely still of late. Kletetschka thinks this is due to water levels. ‘The reason for stones not moving recently is the presence of an artificial trench, draining the excess water from the Playa,’ he says.

No comments:

Post a Comment