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Earth

Scientists Solve Mystery of Ireland's Moving Boulders 127

Hugh Pickens writes "How has a 78-ton boulder traveled 130 meters inland from the sea since 1991? Live Science reports that geologists have puzzled for years over the mysterious boulders that litter the desolate coastline of Ireland's Aran Islands that somehow move on their own when no one is looking. The sizes of the boulders in the formations range 'from merely impressive to mind-bogglingly stupendous,' writes geoscientist Rónadh Cox. While some researchers contend that only a tsunami could push these stones, new research finds that plain old ocean waves, with the help of some strong storms, do the job. Some boulders move inland at an average rate of nearly 3 meters per decade, with one rock moving 3.5 meters vertically and 69 meters horizontally in one year. The team compared modern high-altitude photos of the coastline to a set of meticulous maps from 1839 that identified the location of the boulders' ridges — nearly 100 years after the most recent tsunami to hit the region, which struck in 1755. The Aran cliffs rise nearly vertically out of the Atlantic (video), leaving very deep water close to the shore. As waves slam into the sheer cliff, that water is abruptly deflected back out toward the oncoming waves. This backflow may amplify subsequent waves resulting an occasional storm wave that is much larger than one would expect. 'There's a tendency to attribute the movement of large objects to tsunami,' says Cox. 'We're saying hold the phone. Big boulders are getting moved by storm waves.'"

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