干旱区生态环境知识资源中心

Discussion of weathering in cold regions has historically been dominated by widespread acceptance of the significance of the freeze-thaw concept among periglacial geomorphologists, and an essentially universal acceptance by those geomorphologists not directly involved in researching the topic. Debris produced by freeze-thaw is frequently deemed to be angular in form and the observation of such debris has been used to identify the former or present operation of this weathering mechanism. Large debris (’blocks’) and small debris (’grains’ or ’flakes’) have been recognised as the outcome of the two scales of freeze-thaw weathering: macrogelivation and microgelivation respectively. However, the fusion of climatic geomorphology and process geomorphology in the ongoing development of the freeze-thaw concept has resulted in the confusion of product with process-whereby microgelivation (producing small products) and macrogelivation (producing large products) are seen, due to the product dichotomy, as distinctly different processes. Despite the recent, highly sophisticated laboratory experimentation on freeze-thaw weathering, this historical-process scale-dichotomy still pervades thinking and experimental evaluation. Here we consider the historical development of microgelivation/macrogelivation and outline what are thought to be fundamental flaws with the concepts and their underpinnings. Built within the two notions are elements of rock properties (’hard’ and ’soft’) and scale issues regarding rock attributes (’solid rock’ and ’existing weaknesses’ in rock) that serve only to confuse the process and scale issues even more. The whole notion of frost-weathered debris having a specific form is also highly spurious, there being no shape attribute that is uniquely diagnostic of frost action and this, in turn, leads to the further problem of process synergy or other processes entirely being the cause of rock failure in cold regions. Ultimately we argue that while there may be a range of product sizes (and shapes) resulting from frost weathering per se the widely invoked scale concepts are fraught with problems and are best dropped-as too are any process-shape connotations. (C) 2010 Elsevier B.V. All rights reserved.