Cavernous weathering, dynamical instability and self‐organization

Abstract

Cavernous weathering may be conceptualized as a self-reinforcing process, characterized by positive feedback within the weathering system. A morphometric study of caverns in the Valley of Fire State Park, Nevada, USA, demonstrates the applicability of a dynamically unstable, or conditionally unstable, model of cavernous weathering systems. Outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering, succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce. A paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale: caverns tend toward minimum interior surface area by developing a spheroidal form, yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface.

Evolutionary inventive problem-solving in biology and architecture: ArchiTRIZ and Material-Ontology

“…Part of the trick is the concentration of humidity and cyclic desiccation (Turkington and Phillips 2004).…”

Dynamical instability in surface permeability characteristics of building sandstones in response to salt accumulation over time

“…The stone decay system is inherently complex (Smith, 1996), and these very small-scale differences across a surface may eventually have larger scale consequences as weathering progresses -especially where variation is greater to begin with, for example, in stones composed of immature, poorly sorted, sediments. The concept of dynamical instability has been used to describe and characterise earth surface systems (Turkington and Philips, 2004). In this context, smallscale anomalies can lead to larger scale effects and divergent behaviours -"highly localized initial variations (even quite minor variations) in weathering resistance… tend to become amplified over time in a process of unstable divergence" (Turkington and Philips, 2004: 667).…”

“…This relates to the earlier mention of heterogeneous pockets (pockets of more or less tightly packed grains, or more or less well cemented grains, indicated by permeability measurements) -spatially organized 'cells' of higher permeability (see also Smith et al, 2008), linked to spatial variability of decay across a single block face. This may contribute to the debate on the formation and development of alveoli (Turkington and Philips, 2004;Viles, 2005b), or any spatially concentrated surface retreat, in that, in response to salt weathering, any heterogeneity may be exaggerated and exploited over time leading to differential weathering and spatially concentrated debris release on a block surface. The present research demonstrates that the concept of dynamical instability may be applied at the scale of a single block, towards explaining why certain concentrated areas of a block face may suffer more severe decay than others -dynamical instability is seen in the increasing range of permeability values over the experimental run, and the 'spottiness' of higher permeability areas developing as regular weathering cycles progress.…”

Using morphospaces to understand tafoni development

“…Viles (2005) clearly uses the term 'cavernous weathering' to encompass a number of forms (notably tafoni and alveoli -see her Fig. 1) as too do Turkington and Phillips (2004). Here it is argued, much as discussed elsewhere for other processes (see Hall et al, 2012), that the foundational terminology 'cavernous weathering' itself creates confusion -is it (cavernous weathering) the 'process' (as actually implied by the term) or the product (the 'cavern') and if it is the 'cavern' then quite what does this encompass; or is it implying (as does appear to be the case) both process and form?…”

“…This, in itself, need not be a problem as this paper argues. Indeed, the very extent and variety of suggested processes is not necessarily unexpected given that cavernous weathering is azonal in occurrence (Turkington and Phillips, 2004) and found in a variety of lithologies (see Mustoe, 1982, Table 1). Given the variety of identified causative processes, the product appears to be a classic 'convergence of form', as already noted by Turkington and Phillips (2004, p. 666).…”