OT--Mystery Of Death Valley
Well, yes, indeed. It's been solved, finally--albeit with only partial completeness, mind you--how the mysterious "sailing" rocks of Death Valley National Park are propelled across the world-famous Racetrack Playa (northern sector of the vast desert park, formerly Death Valley National Monument, now with the assimilation of adjacent Wilderness lands in 1994 larger than the entire state of Connecticut).
One must note, of course, that the researchers admit that they can only explain the physical mechanisms that propel pebbles and the smaller chunks of rocks across Racetrack Playa; they haven't yet witnessed, neither can they describe decisively, how the behemoths move, the plus-two hundred pound stone specimens that also leave trails, signifying previous, mysterious unobserved movements.
For a primer on the subject, check out https://scripps.ucsd.edu/news/mystery-solved-sailing-stones-death-valley-seen-action-first-time to read what investigators consider some of the answers. While the actual scientific paper that documents with detailed specificity the discoveries has been embargoed pending formal publication in the appropriate professional scientific journal, the above link nevertheless provides a splendid general overview of the study. Be sure to click on the two videos over at the right of the text. Observe in time-lapse photography a rock actually moving across Death Valley's Racetrack Playa.
There are now two known explanations to account for the Racetrack moving rocks: (1) pebble-sized stones that leave behind trails in the mud float out onto the playa on rafts of ice, a scenario long-suspected, of course, but never definitively proved, though this specific method admittedly accounts only for the diminutive rocks, not the modest chunk-sized somewhat larger specimens that also create trails; and (2), for medium-sized rock chunks only, the basic idea is that combined with a rare, substantial precipitation event over the playa, providing adequate rainfall to engulf, but not submerge the rocks scattered across the playa, you also need necessary freezing temperatures at night, just low enough to create thin, veneer-like sheets of ice only a few millimeters thick.
Next, comes the morning--and, LIVE ACTION, indeed. What happens next is that you need a sun warm enough to partially melt the ice sheets that have formed around the perimeters of individual rocks: that is to say, sunlight preferentially heats the dark-colored stones to melt all ice in direct contact with them.
Yet, simultaneously, as ice gradually melts out on the playa, temperatures must remain moderately low enough to allow those now separating ice sheets to persist in patches, never entirely disappearing--so that when even rather mild wind gusts occur, the now isolated thin ice sheets begin to move, pushing against neighboring stationary playa rocks, eventually ramming the rocks, causing the stones to move ever so slowly--so slowly, in fact, that the researchers remark that you could be standing right next to one and probably never even notice that it's actually in motion; indeed, they postulate than perhaps several individuals during the historical past have indeed been present when the rocks move under such restrictive weather conditions, yet could never detect the activity.
In conclusion, the investigators speculate that such a relatively rare combination of meteorological events conspires to slide the Racetrack Playa rocks no more than once every ten years.
My page, "Fossils In Death Valley National Park"
From Inyo - September 01, 2014 at 05:58:00