GEOMOR-03394; No of Pages 8 Geomorphology xxx (2010) xxx–xxx Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph The historical legacy of spatial scales in freeze–thaw weathering: Misrepresentation and resulting misdirection Kevin Hall a,⁎, Colin Thorn b a Department of Geography, Geoinformatics & Meteorology, University of Pretoria, Pretoria, 0002, South Africa b Department of Geography, University of Illinois at Urbana-Champaign, 220 Davenport Hall, 607 South Mathews, Urbana, IL 61801, USA article info abstract Article history: Discussion of weathering in cold regions has historically been dominated by widespread acceptance of the Received 23 July 2008 significance of the freeze–thaw concept among periglacial geomorphologists, and an essentially universal Received in revised form 16 July 2009 acceptance by those geomorphologists not directly involved in researching the topic. Debris produced by Accepted 4 October 2010 freeze–thaw is frequently deemed to be angular in form and the observation of such debris has been used to Available online xxxx 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: Keywords: Weathering macrogélivation and microgélivation respectively. However, the fusion of climatic geomorphology and Freeze–thaw process geomorphology in the ongoing development of the freeze–thaw concept has resulted in the confusion Microgélivation of product with process—whereby microgélivation (producing small products) and macrogélivation Macrogélivation (producing large products) are seen, due to the product dichotomy, as distinctly different processes. Despite Process-product scales 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 microgélivation/macrogélivation 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. © 2010 Published by Elsevier B.V. 1. Introduction geomorphology. These considerations are pervaded with scale concepts varying from the scale of the processes and of the landforms to the use of Geomorphologists consider landforms to be the product of geomor- scale-defined terminology, and finally to the broad scientificcontextof phic processes and, in turn, influence those processes. They recognize scale concepts. Our objective is to illuminate how the legacy of that this interaction is sensitive to initial conditions (e.g., Phillips, 1988, geomorphic thinking has constrained and steered contemporary 1999), plays out at multiple spatial and temporal scales (Schumm and research into freeze–thaw weathering including the role scale has Lichty, 1965), and that the process–form interactions they choose to played and is playing in the matter. Freeze–thaw weathering, broadly invoke may change through time (e.g., Haff, 1996). Such a claim raises a the belief that the alternate freezing and thawing of hydrated materials deep philosophical issue—are geomorphologists identifying natural (especially rock) on short (e.g., diurnal or synoptic) or longer (e.g., kinds when they identify landforms, or are they carving categories from seasonal) scales breaks them up, is widely invoked by periglacial a landscape continuum (Rhoads and Thorn, 1996a)? Here we skirt such geomorphologists, and essentially universally-accepted as active in ‘deep philosophy’, preferring to focus upon the ‘shallow philosophy’ periglacial regions by geomorphologists not actively engaged in cold (often called ‘methodology’) associated with everyday terminology, the region research. As such it is an important geomorphic concept that interpretation of field evidence, and the nature of experimental needs to be well-founded and clearly conceptualized or defined. Fundamentally, a geomorphologist seeks to explain a (land)form by understanding the interaction between process and material. It seems intuitively reasonable to assign the process(es) a causal role ⁎ Corresponding author. Present address: Geography Programme, University of fl Northern British Columbia, 3333 University Way, Prince George, BC, V2N 4Z9, Canada. and the landform one of effect. However, this clearly con ates the E-mail addresses: [email protected] (K. Hall), [email protected] (C. Thorn). process and the material and it is much less clear how these two 0169-555X/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.geomorph.2010.10.003 Please cite this article as: Hall, K., Thorn, C., The historical legacy of spatial scales in freeze–thaw weathering: Misrepresentation and resulting misdirection, Geomorphology (2010), doi:10.1016/j.geomorph.2010.10.003 2 K. Hall, C. Thorn / Geomorphology xxx (2010) xxx–xxx interact. Indeed, clearly the material also has some casual, as well as “frost penetrates deeply enough to freeze water contained in joints” and effect, role. There is no a priori reason to believe that the scale of a “springs (presumably this could/should also be translated as ‘heaves’) geomorphic process, as opposed to the characteristics of the material, joint blocks of several cubic metres” (Tricart, 1970,p.115).Micro- inevitably controls the scale of the geomorphic product—the gélivation on the other hand, occurs where “night frost succeeds in landform. Furthermore, if a landform is the product of the interaction reducing to sand and gravel, extremely hard volcanic rocks” (Tricart, between a geomorphic process (the driving force) and an existing 1970, p. 115). Thus, large amplitude, long duration freezes produce material there is no inherent reason to believe that: 1) the same (only) large material while short duration freezes can only produce driving force will always produce the same resulting landform (the small sized material: a process–product scale relationship. The evidence forward-looking view); 2) any form is necessarily always the product of both large blocks and fine material in cold regions adds visible of the same process (the backward-looking view); and 3) driving credence to the distinction. At this juncture we might identify Tricart as forces might not be constrained or dictated by the initial nature of the using ‘morphogenic’ terms—such terms are not only descriptive but material. Finally, the explanation of any existent landform assemblage inherently connote the origin of the form as well. Morphogenetic (landscape) is always plagued by largely uncertain initial conditions, terminology is widespread in geomorphology and has consistently changing environment(s) or inheritance (temporal contamination), plagued the discipline as theory has progressed, thereby bypassing the and interference (spatial contamination). genetic component of a term while researchers have sought to retain the descriptive (morphological) component. This has usually resulted in the 2. Terminology messy use of an established morphogenetic term supposedly shriven of its genetic connotations. A classic example of this would be the way that Historically geomorphology was essentially an ‘eye-ball’ science the Davisian term ‘peneplain’ has often been used subsequently to mean and geomorphologists investigating the nature of freeze–thaw ‘an eroded regional surface’, but the user has not subscribed to the weathering appear to have conflated the process and the product. development components of the Davisian landscape model. As we have addressed this issue previously (e.g., Thorn, 1979; Hall et However, Tricart's (1970, p. 76) position is actually much more al., 2002) the reader is referred to these earlier publications where this complicated because he also states that “sedimentary rocks are more admittedly rather sweeping generalization is generously referenced. subject to microgélivation, the less they are compacted.” The issue Furthermore, many periglacial geomorphologists seem to have becomes even more convoluted when Tricart (1970, p. 76) states assigned an uncertain, sometimes unrecognized, or variable role to “Macrogélivation exploits existing weaknesses in the rock; micro- the material(s) involved. The result is that the nature of the process gélivation cuts into solid rock” and then proceeds to claim that (es) remains(remain) uncertain and is(are) still commonly viewed “Weathered crystals are at once less resistant to pressure and more and understood in terms of the ensuing products (landforms or permeable; it is these that microgélivation exploits”. Quite how landform elements). This conflation of ‘process’ and ‘product’ is well weathered crystals are ‘solid rock’ is not clear (see