Revisiting dirt cracking as a physical weathering process in warm deserts

摘要: Abstract A half century ago C.D. Ollier proposed that insolation-driven temperature changes expand and contract fill in fissures enough to widen cracks, a process would permit progressively deeper penetration of fissure fills, turn generate positive feedback greater strain until desert boulders bedrock shatters. Although physical weathering by “dirt cracking” has occasionally been cited, this hypothesized remains without support from subsequent research. Here, field observations, electron microscopy, X-ray powder diffraction, particle-size analysis, laboratory experiments shed new light on dirt cracking. Little clear evidence supports the original notion expansive pressures thermal fluctuations. However, mineralogical, high resolution transmission back-scattered experimental two alternative processes widening fractures: wetting drying fills inside fissures; precipitation remobilization calcium carbonate. re-envisioned dirt-cracking wedging starts with carbonate precipitating less than 5 μm wide. First precipitation, then ongoing dissolution laminar calcrete, opens space for dust penetrate into these narrow fractures. Wetting clays exerts pressure deepen fissure, allowing even more move fracture. As infiltrates, its texture chaotic mix particles an alignment parallel sides. This could increase efficiency wedging. Ollier's concept supported; each increment fracture deepening permits more, infiltration calcrete dust. Field microscope observations rock spalling winter 2010 are consistent hypothesis cracking is common deserts splits rocks all different sizes.