Glassy dynamics of landscape evolution

TL;DR

This paper reveals that hillslope soil transport exhibits glassy dynamics similar to disordered materials, with a transition from creep to flow at a critical gradient, and introduces a model that predicts landscape evolution.

Contribution

It introduces a granular physics-based model capturing the full spectrum of hillslope behaviors, from creep to landslides, based on grain-scale friction.

Findings

Creep occurs below a critical slope gradient.

A continuous transition to dense granular flow at the critical point.

The model accurately reproduces natural hillslope profiles.

Abstract

Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by Discrete Element Method simulations, and re-analysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales.