저절로 움직이는 돌의 미스터리 풀렸다 Mystery of sliding rocks in Death Valley finally solved VIDEO
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저절로 움직이는 돌이 있다.
미국 캘리포니아의 데스밸리(Death Valley) 국립공원에는 바닥에 자국을 내며 움직이는 돌이 자주 목격된다. 데스밸리는 물이 말라 붙어 사막처럼 생명체가 거의 없는 곳이다.
세일링스톤(sailing stone)이라고 불리는 이들 돌은 데스밸리 국립공원의 마른 호수 레이스트랙 플라야에 가면 볼 수 있다.
강한 바람에 굴러가는 게 아니냐고? 아니다. 돌은 웬만한 바람에는 꿈쩍하지 않을 정도로 크고 무게도 상당한 것들이다.
도대체 어떻게 된 일일까? 최근에야 미스터리가 풀렸다.
뉴시스가 최근 보도한 바에 따르면 캘리포니아 스크립스 해양연구소에서 일하는 리처드 노리스 박사와 사촌인제임스 노리스 박사가 연구를 통해 원인을 밝혀냈다.
마른 호수인 레이스트랙플라야에도 아주 드물지만 비가 내린다. 밤에 내린 비가 얼었다 해가 뜨면서 녹을 때 마른 땅이 진흙 미끄러워지고 이 때 바람이 불면 돌이 아주 조금씩 움직이게 된다는 것이다.
돌이 움직이는 속도는 분당 4.6m로 느리다고 한다. 아래 영상에는 세일링스톤의 다양한 모습이 담겨 있다.
허핑턴포스트코리아 | 작성자 권복기 |
Mystery of sliding rocks in Death Valley finally solved
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By Joyce Lupiani. CREATED Aug 30, 2014
Visitors to Death Valley noticed the phenomenon nearly a century ago, according to Live Science. Hundreds of rocks from pebbles to 700 pound boulders somehow moved across the surface of a dry lake bed named Racetrack Playa, leaving long tracks behind.
But no one could explain how it happened even though many attempted to solve the puzzle since the 1940s.
Apparently, the mysterious movement is caused by floating ice. Yes, there is water and ice in one of the hottest places on Earth.
It works like this: Step one is that the playa has to fill with just the right amount of water, deep enough for the ice to form when it is cold but shallow enough to expose the rocks. Next, the "pond" freezes and turns into windowpane ice. That means the ice is thin enough to move freely, but still thick enough to not break apart easily.
When that ice begins to melt, it starts breaking into sheets. These sheets are pushed by the wind across the shallow pond.As the sheets of "windowpane" ice move, they push the rocks in front of them, which leaves trails in the soft mud.
Richard Norris, a paleobiologist from Scripps Institution of Oceanography at the University of California, San Diego, his cousin James Norris, who is an engineer, and planetary scientist Ralph Lorenz are responsible for figuring it out. The results were published in the journal PLOS One on Wednesday.
After getting permission from the National Park Service, the cousins traveled to the remote playa in Eastern California in 2011 and left behind 15 special rocks embedded with motion-activated GPS sensors. They also installed a weather station to track the wind on the playa.
For two years, nothing happened. During that time, they met Lorenz, who had been researching the stones since 2006.
In December 2013, the cousins drove back to the playa and were amazed when they actually witnessed the rocks moving. James Norris caught the action in a series of still pictures and turned it into a movie.
Several wet winter storms created the perfect conditions for sliding rocks from December 2013 to February 2014. The researchers were able to chart individual rock slides that lasted from only a few seconds to as long as 16 minutes. They also recorded rocks that were three football field lengths apart that move at the same time for more than 200 feet in a single trip.
However, they never saw the really big rocks move and aren't sure that it is the exact same process.
But, they may have solved another mystery. Park rangers would sometimes observe trails but no rocks. They thought visitors were stealing them. It is now believed the trails were caused by the sheets of ice themselves.
This wasn't actually the first time that someone guessed that wind, water and ice were involved. But, it is the first time that is was proven and observed. Until then, it was simply speculation.
The other big surprise was that it actually took very little wind to make it all happen.
Richard Norris says that he knows some people who like the mystery of the sliding rocks will probably be disappointed that it has been solved. Joyce Lupiani |
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