Avalanches on Saturn's Moon Provide Clue to Landslides on Earth

Huge landslides or avalanche are rare occurrences in the solar system but very common phenomenon on Saturn's third largest moon Lapetus. These are helping geologists in understanding landslides and earthquakes in other parts of the solar system.

William McKinnon, professor of earth and planetary sciences 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. So there's a lot of topography and it's just sitting around, and then, from time to time, it gives way."

Scientists identified a strange feature of the avalanches. At high speeds, the falling ice begins to behave like a liquid, travelling many miles before finally coming to rest. Experts are trying to explain a similar phenomenon of landslides and earthquakes on Earth.

In the July 29 issue of Nature Geoscience, Kelsi Singer, McKinnon and colleagues Paul M. Schenk of the Lunar and Planetary Institute and Jeffrey M. Moore of the NASA Ames Research Center, describe these giant ice avalanches.

"The landslides on Lapetus are a planetary scale experiment that we cannot do in a laboratory or observe on Earth," said study co-author Singer also at WUSTL in a release. "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 Lapetus."

They researchers state that the coefficient of friction of the avalanches is not consistent with the coefficients of friction of very cold ice measured in the laboratory. The coefficients for the Lapetus avalanches, however, scatter between 0.1 and 0.3. Something is off here.

Geologists now realize that major faults are weaker during earthquakes than laboratory measurements of rocks' coefficients of friction suggest they should be.

Nobody is sure what lubricates the faults when they are jolted into motion by an earthquake, but one of the simplest hypotheses is something called flash heating, Singer says. The idea is that as the rocks slide past one another, asperities (tiny contact points) on their surfaces are heated by friction.

"You might think friction is trivial," McKinnon says, "but it's not. And that goes for friction between ices and friction between rocks. It's really important not just for landslides, but also for earthquakes and even for the stability of the land. And that's why these observations on an ice moon are interesting and thought-provoking."