Dan's Outside

I go, I see, I do, I walk, I think, I like…

About Those Rocks

“Stacy” sent a nice note about my web site (thanks!) and asked about the moving rocks at Racetrack Playa in Death Valley:

“I was wondering if you knew how the rocks moved across the surface like your pictures show. Wind?”

RacetrackRocksClouds2006|04|03: Rocks and Clouds, Racetrack Playa. Death Valley National Park. April 3, 2006. © Copyright G Dan Mitchell.

Rocks and Clouds, Racetrack Playa. Death Valley National Park. April 3, 2006. © Copyright G Dan Mitchell.

The playa is essentialy a very flat dry lakebed formed of fine silt washed down from the surrounding mountains. The first theory I read suggested that the seasonally-wet playa surface was slick enough that extremely strong winds could move the rocks. The winds are quite strong there and apparent do frequently blow from the rocky hill at the end of the playa. (This hill is seen in the photo below.) However, I believe that someone eventually calculated that winds would have to blow at many hundreds of miles per hours to move some of the very large and heavy rocks.

ApproachingRocks2006|04|03: Approaching Rocks, Racetrack Playa. Death Valley National Park. April 3, 2006. © Copyright G Dan Mitchell.

Approaching Rocks, Racetrack Playa. Death Valley National Park. April 3, 2006. © Copyright G Dan Mitchell.

The more recent theory arose from the above realization combined with the observation that the tracks on the playa demonstrate that groups of rocks sometimes move as if locked together. As I understand it, under the right conditions shallow surface water on the playa can freeze, locking the rocks in a large, shallow ice sheet. (Yes, Death Valley can get cold in the winter.) The wind acts on the large surface of frozen water, dragging the embedded rocks over the slick surface. This seems like a reasonable explanation to me, though I don’t believe anyone has ever actually observed the process in action.

As far as I know, Racetrack Playa is the only place in the world where you can see this phenomenon. If you ever get the opportunity to visit Racetrack Playa, do go. Even without the moving rocks, dawn on the playa is not to be missed.

(Note: The 60-mile round trip drive on a rough gravel road to Racetrack Playa is not for the faint of heart and requires a sturdy vehicle. At certain times of the year it would be dangerous and downright foolish to try to get there. Check with Death Valley National Park and other experts before trying it.)
—–

Advertisements

August 14, 2006 - Posted by | Commentary

Sorry, the comment form is closed at this time.

%d bloggers like this: