Nicola Guttridge, contributor
(Image: NASA/JPL/Space Science Institute)
Icy peaks, moonquakes, squashed poles and towering mountain ridges taller than Everest - chilly Iapetus, one of Saturn's many moons, is an odd place. When the wall of the Malun crater broke and plummeted some 8 kilometres to the crater floor, the falling ice created yet more strangeness - a strangely far-reaching landslide.
Iapetus is known to experience landslides - ice on the surface of the small body tumbles from its lofty ridges and peaks, picking up speed as it falls. When the ice is moving fast enough, it begins to flow rather than tumble, acting like a fluid. The material from the rim of the Malun crater, photographed here by the Cassini probe, surged a staggering 35 km from the base of the crater wall - some four times the vertical distance - before finally slowing to a halt.
This behaviour isn't completely alien - as well as seeing these slides on the surfaces of Iapetus and Mars, we experience them on Earth as sturzstrom, literally "fall-stream". However, the Iapetus slides are puzzling because of the immense distances covered by the run-out material - on Earth, landslides tend to stop at less than twice the distance fallen, but these icy slides can travel up to 30 times their fall distance.
Planetary scientist Kelsi Singer of Washington University in St Louis and colleagues believe that this is due to something known as flash heating, which heats the tumbling material and helps it keep moving by effectively lowering the friction it experiences. At high enough speeds, points where the fragments touch could become so hot they could weaken the avalanche material, making it easier for it to continue flowing onwards.
Journal reference: Nature Geoscience, DOI: 10.1038/ngeo1526
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