Dynamics, mobility-controlling factors and transport mechanisms of rapid long-runout rock avalanches in China

• Forty-three rapid and long-runout rock avalanches in China are selected for study.
• Dynamic course of the rock avalanches is summarized and classified into five types.
• Occurrence conditions of the rock avalanches of each dynamic type are obtained.
• Factors controlling mobility of the rock avalanches are obtained through statistics.
• Transport mechanisms are revealed through studying four of selected rock avalanches.

The dynamics and occurrence conditions of 43 rapid and long run-out rock avalanches in China were summarized. Their dynamics were classified into 5 types. The standard dynamic type was designated to be “fail, squirt and flow”, where part of the landslide path always has a parabolic airborne course because the slide body has an initial speed and the toe of the surface of rupture projects the landslide into the air. The occurrence conditions of rock avalanches of the standard dynamic type are huge kinetic energy, elevated toe to the surface of rupture and enough transport space to run out into. The occurrence conditions of the other four types were then compared with the standard dynamic type. Statistical analysis showed that volume, topography, huge kinetic energy and an elevated toe to the surface of rupture were the principal factors controlling mobility in the rock avalanches. Four of the rapid long run-out rock avalanches, each in a different geological setting, were then examined in more detail to reveal the transport mechanisms leading to their high speed and long runout. The results suggested that besides their huge kinetic energy, high pore water pressure produced by undrained shear and elastic energy released by grain fragmentation were the main transport mechanisms contributing to the long travel distances and high speeds of rock avalanches. Field investigation indicated that air was involved during the transport, but whether it influenced the transport or how much the influence was is still much disputed.