The vast diversity of landscapes found on Earth results from interplay between processes that break rock down, produce mobile regolith, and transport materials away. Mechanical weathering is fundamental to shaping landscapes, yet it is perhaps less understood at a mechanistic level than chemical weathering. Ubiquitous microfractures in rock propagate and grow through a slow process known as subcritical cracking that operates at the low applied stresses common in the near-surface. Subcritical cracking is the most likely explanation for the mechanical processes associated with thermal stress, ice lens growth, mineral alteration, and root growth. The long timescales over which critical zone architectures develop require an understanding of slow processes, such as subcritical cracking.