Flume experiments on the mobility of landslides with erosion

Landslides are highly dynamic events in which the erosion and entrainment of basal sediment can greatly enhance landslide mobility and energy, extending travel distances and intensifying impact forces. Understanding under which erosive conditions the mobility of landslides will be enhanced or reduced, thus, is critical for improving hazard assessments. Yet, empirical models are still limited in quantifying and predicting these dynamics accurately, due to an insufficient understanding of the underlying physical conditions.

We aim to experimentally test and verify a recently proposed mechanical model for the mobility of erosive landslides (Pudasaini & Krautblatter, 2021). This model suggests that landslide mobility is governed by three distinct erosion-driven energy regimes (gain, loss, or neutrality), arising from the change in inertia and momentum production as bed material is eroded and entrained. Our goal is to generate laboratory landslides that maintain a uniform flow at the landslide-bed erosion interface to enable precise velocity measurements of sliding mass, erosion, and entrainment under pre-defined mechanical conditions. We developed an experimental setup, inclinable to 40° and comprising a 5 m long and 0.25 m wide landslide flume with transparent sidewalls, to study sediment transport processes across a 2 m long erodible bed in two dimensions. To achieve the proposed landslide energy regimes of gain, loss, or neutrality, the erodible bed is designed to be inertially weaker, stronger, or neutral relative to an initial sliding mass. For single-phase flows, this is accomplished by using different granular bed materials of varying densities relative to the initial sliding mass. For two-phase flows, the water content of the bed is adjusted relative to that of the initial sliding mass.

Here we present new experiments on dry and partially saturated flows suggesting that the inertia of the erodible bed influences slide mobility and affects the deposition morphology. We further show how Particle Tracking Velocimetry can be used to distinguish between landslide, erosion and entrainment velocities, which is essential for the calibration and validation of the proposed theoretical framework.