Credit: Jon White/Colorado Geological Survey

Vibrations that ripple through rocks as they tumble downhill explain why some landslides travel farther than expected. The finding could help towns to better prepare for landslide hazards.

In 'long runout' landslides, falling rocks can move tens to hundreds of kilometres on flat land — more than ten times the height from which they fell. A team led by Brandon Johnson of Brown University in Providence, Rhode Island, modelled the forces in such landslides. The scientists found that vibrations caused by slides of sufficient size reduce the pressure between rock fragments, effectively lowering friction and allowing the rocks to flow like a fluid over long distances.

A similar effect could also occur along geological faults during earthquakes.

J. Geophys. Res. Earth Surf. (2016)