Silica Pond, Iceland
One of the highlights of the interior of Iceland: a hot-water pond, charged with silica, glowing in the middle of nowhere
16 The Sliding Rocks of Racetrack Playa
One of the most interesting mysteries of Death Valley National Park is the sliding rocks at Racetrack Playa (a playa is a dry lake bed). These rocks can be found on the floor of the playa with long trails behind them. Somehow these rocks slide across the playa, cutting a furrow in the sediment as they move.
Some of these rocks weigh several hundred pounds. That makes the question: "How do they move?" a very challenging one.
The truth: No one knows for sure exactly how these rocks move - although a few people have come up with some pretty good explanations. The reason why their movement remains a mystery: No one has ever seen them in motion!
About Racetrack Playa :
Racetrack playa is lake bed that is almost perfectly flat and almost always dry. It is about 4 kilometers long (2.5 miles - north to south) and about 2 kilometers wide (1.25 miles - east to west). The surface is covered with mudcracks and the sediment is made up mainly of silt and clay.
The climate in this area is arid. It rains just a couple of inches per year. However, when it rains, the steep mountains which surround Racetrack Playa produce a large amount of runoff that converts the playa floor into a broad shallow lake. When wet, the surface of the playa is transformed into a very soft and very slippery mud.
