Slow-to-fast transition of giant creeping rockslides modulated by undrained loading in basal shear zones

Federico Agliardi,Cristiano Collettini,Nicoletta Fusi,Marco M Scuderi

doi:10.1038/s41467-020-15093-3

Abstract

Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. They creep slowly for centuries and then can fail catastrophically posing major threats to society. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse remain elusive. We couple laboratory experiments on natural rockslide shear zone material and in situ observations to provide a scale-independent demonstration that short-term pore fluid pressure variations originate a full spectrum of creep styles, modulated by slip-induced undrained conditions. Shear zones respond to pore pressure increments by impulsive acceleration and dilatancy, causing spontaneous deceleration followed by sustained steady-rate creep. Increasing pore pressure results in high creep rates and eventual collapse. Laboratory experiments quantitatively capture the in situ behavior of giant rockslides and lay physically-based foundations to understand the collapse of giant rockslides.

Highlights

Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios
We demonstrate that the spectrum of rockslide creep styles until catastrophic collapse is regulated by undrained hydro-mechanical response to short-term fluid pressure perturbations
The analysis of subsurface investigation and monitoring data, including high-quality drillcores, borehole inclinometer measurements, topographic and extensometer surface displacements data, suggest that the rockslide mass is affected by relatively small internal deformation[9,44,45], so that long-term surface displacements are mainly related to hydro-mechanical forcing along the basal shear zone

Summary

Introduction

Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. Giant creeping rockslides in crystalline rocks represent major threats to human life and infrastructures[1,2] due to their volume (106–108 m3) and fragmentation potential, resulting in extremely high kinetic energy mobilization if massive collapse occurs[3,4] These landslides evolve over thousands of years and establishing reliable criteria to predict their critical transition to fast movements and catastrophic failure remains challenging[5,6,7]. Large natural slopes are sub-critically stressed (i.e., subjected to stress condition slightly lower than their instantaneous strength) and respond to major geomorphic perturbations (e.g., river incision in uplifting settings, glaciation/deglaciation) by progressive rock failure processes[8,9] Over time, these processes lead to rock damage accumulation and permeability enhancement, until strain localizes along basal shear zones similar to tectonic faults[10,11,12]. Useful and relatively easy to apply, these approaches are unable to account for the full spectrum of rockslide slip behaviors, and leave considerable uncertainties that impact the reliability of forecasting models and early warning criteria[28]

Methods

Results

Conclusion