1 Introduction

The in situ mechanical breakdown, or physical weathering, of rock at and near Earth's surface constitutes a critical component of a wide array of surface process systems ranging from river channels (Hancock et al. 2011) to mass wasting (Collins and Stock 2016) to long-term landscape evolution (Kirchner et al. 2006). The relative importance of various weathering processes (freezing, thermal cycling, mineral hydration, etc.) in contributing to these systems, however, remains unknown, resulting in an overall lack of understanding of the key driving and limiting factors of rock breakdown and erosion (Portenga and Bierman 2011). Here we take a new approach to evaluating mechanical weathering and associated rock erosion by exploring these processes in the context of climate-dependent subcritical crack growth.

The role that subcritical crack growth (a.k.a. time-dependent crack growth, progressive rock fracture) may play in mechanical weathering and subsequent rock erosion has never been substantially characterized. Based on a compendium of existing fracture mechanics data and theory (Eppes and Keanini, in prep), the following hypotheses arise:

  1. subcritical crack growth is a viable, and likely common, mechanism of mechanical weathering acting in concert with all weathering-induced stresses at and near Earth's surface,

  2. rates of subcritical crack growth in all weathering environments are climate–dependent, outside of climate's influence on individual stress loading via processes like freezing or mineral hydration, and therefore

  3. rates of erosion for any given rock type will be strongly influenced by that rock's subcritical crack growth characteristics, such as its fracture toughness or its subcritical crack growth index (n), the latter of which is itself also known to be climate- dependant. In testing these hypotheses we explore a potentially universal mechanism of rock breakdown at and near Earth's surface.

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