Mechanical weathering and rock erosion by climate‐dependent subcritical cracking

TLDR

The study develops a fracture‑mechanics framework to conceptualize mechanical rock breakdown, regolith production, and erosion on Earth and other terrestrial bodies. The authors build physically based subcritical cracking and rock‑erosion models grounded in fracture mechanics, showing that climate‑dependent chemophysical bond‑breaking at crack tips drives subcritical cracking rates. The analysis shows that mechanical weathering in most rock types proceeds via climate‑dependent subcritical cracking, which can cause significant erosion under stresses below rock strength, with humidity accelerating cracking exponentially and rates sensitive to environmental and material properties, while confining pressure may suppress it.

Abstract

Abstract This work constructs a fracture mechanics framework for conceptualizing mechanical rock breakdown and consequent regolith production and erosion on the surface of Earth and other terrestrial bodies. Here our analysis of fracture mechanics literature explicitly establishes for the first time that all mechanical weathering in most rock types likely progresses by climate‐dependent subcritical cracking under virtually all Earth surface and near‐surface environmental conditions. We substantiate and quantify this finding through development of physically based subcritical cracking and rock erosion models founded in well‐vetted fracture mechanics and mechanical weathering, theory, and observation. The models show that subcritical cracking can culminate in significant rock fracture and erosion under commonly experienced environmental stress magnitudes that are significantly lower than rock critical strength. Our calculations also indicate that climate strongly influences subcritical cracking—and thus rock weathering rates—irrespective of the source of the stress (e.g., freezing, thermal cycling, and unloading). The climate dependence of subcritical cracking rates is due to the chemophysical processes acting to break bonds at crack tips experiencing these low stresses. We find that for any stress or combination of stresses lower than a rock's critical strength, linear increases in humidity lead to exponential acceleration of subcritical cracking and associated rock erosion. Our modeling also shows that these rates are sensitive to numerous other environment, rock, and mineral properties that are currently not well characterized. We propose that confining pressure from overlying soil or rock may serve to suppress subcritical cracking in near‐surface environments. These results are applicable to all weathering processes.