Unveiling the role of seepage forces in the acceleration of landslides creep

TL;DR

This study reveals that seepage forces, rather than fluid pressure, primarily drive landslide creep accelerations, challenging traditional theories and offering new insights into landslide stability and hazard mitigation.

Contribution

The paper introduces a micromechanical model that isolates seepage forces as the main factor in landslide creep, supported by detailed field measurements.

Findings

Seepage forces are the dominant driver of creep accelerations.

Low fluid pressure across the shear zone challenges fluid-driven instability theories.

The model's broader applicability to other geological contexts is discussed.

Abstract

In the context of global climate change, geological materials are increasingly destabilized by water flow and infiltration. We study the creeping dynamics of a densely monitored landslide in Western Norway to decipher the role of fluid flow in destabilizing this landslide. In {\AA}knes, approximately 50 million cubic meter of rock mass continuously creeps over a shear zone made of rock fragments, with seasonal accelerations that strongly correlate with rainfall. In this natural laboratory for fluid-induced frictional creep, unprecedented monitoring equipment reveals low fluid pressure across the shear zone, thereby challenging the dominant theory of fluid-driven instability in landslides. Here, we show that a generic micromechanical model can disentangle the effects of fluid flow from those of fluid pressure, and demonstrate that seepage forces applied by channelized flow along the shear zone are the main driver of creep accelerations. We conclude by discussing the significance of seepage forces, the implications for hazard mitigation and the broader applicability of our model to various geological contexts governed by friction across saturated shear zones.