Saturn moon's landslides attract study

Long, icy landslides on a moon of Saturn resemble ones on Earth known to travel a distance up to 30 times the height from which they fall, U.S. researchers say. The discovery on the moon Iapetus could provide clues to extreme slippages elsewhere in the solar system and how they happen, they said. "We see landslides everywhere in the solar system," said Kelsi Singer, graduate student in earth and planetary sciences at Washington University in St. Louis, "but Saturn's icy moon Iapetus has more giant landslides than any body other than Mars." Iapetus' spectacular topography -- one half of it is light-colored and the other half is dark, it has mountains twice the height of Mount Everest, and a mountainous ridge encircling its equator gives it the distinct appearance of a walnut -- is the reason, researchers said. "Not only is the moon out-of-round, but the giant impact basins are very deep, and there's this great mountain ridge that's 20 kilometers (12 miles) high, far higher than Mount Everest," earth and planetary scientist William McKinnon said. "So there's a lot of topography and it's just sitting around, and then, from time to time, it gives way," McKinnon said. Falling from such heights the ice reaches high speeds, its coefficient of friction drops, and it begins to flow rather than tumble and travels many miles before it dissipates the energy of the fall and finally comes to rest. Similar long-runout landslides on Earth are known as sturzstroms (German for fallstreams), and one of the best known is the prehistoric Blackhawk landslide in southern California. "The landslides on Iapetus are a planet-scale experiment that we cannot do in a laboratory or observe on Earth," Singer said. "They give us examples of giant landslides in ice, instead of rock, with a different gravity, and no atmosphere. So any theory of long-runout landslides on Earth must also work for avalanches on Iapetus."