Rock weathering

Frost weathering processes involve (1) volumetric expansion as liquid water changes to ice within rock or mineral particles, and (2) migration of liquid water toward freezing sites where growing ice lenses fracture rock (ice segregation). Mechanical weathering processes unrelated to ice formation include hydration shattering in clay-rich rocks and thermally-induced stress near rock surfaces. Chemical and biological weathering processes are also active in many periglacial and permafrost regions, with rates of chemical erosion in mid-latitude alpine periglacial environments (9–100 t km–2 year–1) broadly similar to the global average for all rock types (45 t km–2 year–1). Rockwall retreat rates in alpine regions have an overall mean of 1.1 mma- 1, distinctly greater than that of 0.3 mm a–1 from arctic regions, though rates likely vary through time. The products of cold-climate weathering include silt- to boulder-sized debris, weathering rinds and chemical rock coatings, a variety of rock-surface features, tors and rockwalls, and weathering profiles characterized by fractures parallel to the cooling surface. Numerical models of frost weathering predict the intensity and depth of rock fracture but remain to be widely validated from field data.