Rates of development of tafoni in the Moenkopi and Kaibab formations in Meteor Crater and on the Colorado Plateau, northeastern Arizona

To describe temporal change in tafone development, an S-shaped curve equation is proposed: Z = Z c [1 − (n + 1) exp (− β t ) + n exp (− (1 + 1/n) β t )] , where Z is observed tafone depth, Z c is ultimate tafone depth, t is time, and n and β are constants. The applicability of this model is examined using tafone data selected from seven sites, which are categorized into three different salt-weathering environments: a spray/splash-dominant (occasionally wave-affected) supra-tidal zone, aerosol-affected coastal regions, and inland desert areas. The results indicate that the equation can well describe tafone development in each of these environments. An investigation based on the values of n and β, determined through a best fit of the equation to the data, suggests that n characterizes site-specific environmental conditions and β reflects the magnitude of factors controlling the recession mechanism of tafone surfaces. It is found that (1) the maximum rate of tafone growth dramatically decreases from supra-tidal, through coastal, to desert environments, and (2) the growing mode of tafoni is different depending on the environmental settings. The erosional force to facilitate the development of tafoni at supra-tidal sites is estimated to be about 400 times greater than that in the general coastal area.

Section: Datasets and Application Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…This development mode is likely to be well described by an S‐shaped curve through time. Norwick and Dexter () proposed a sigmoidal equation for this:

Z = C_{2} + exp (C_{3} + (C_{4} / t))

Section: Introductionmentioning

confidence: 99%

“…This development mode is likely to be well described by an S-shaped curve through time. Norwick and Dexter (2002) proposed a sigmoidal equation for this:…”

Section: Introductionmentioning

confidence: 99%

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Application of an S‐shaped curve model to the temporal development of tafoni of salt‐weathering origin

Sunamura¹,

Aoki

2011

“…Originally, Cooke et al (1993) indicated tafoni as cavities of several cubic metres in volume, but it seems more appropriate to follow the definition proposed by Turkington and Phillips (2004), in which 'all discrete hollows of measurable size' are considered tafoni. Tafoni occur on different kinds of substrate, generally on granular rocks such as sandstone, granite, tuff and conglomerate (Dragovich, 1969;Martini, 1978;Kejonen et al, 1988;Matsukura et al, 1989;Mellor et al, 1997;Matsukura et al, 1999;McBride and Picard, 2000;Matsukura and Tanaka, 2000;Una Alvarez, 2004) and to a lesser extent on other kinds of rock such as limestone (Smith, 1978;Norwick and Dexter, 2002), dolerite (Conca and Astor, 1987) and various metamorphics (Reusch, 1882;Kejonen et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Tafoni development in a cryotic environment: an example from Northern Victoria Land, Antarctica

Strini

Guglielmin

Hall

2007

Tafoni are a type of cavernous weathering widespread around the world. Despite the extensive distribution of the tafoni, their genesis is not clear and is still a matter of debate, also because the), occur in such different climatic conditions and on so many different types (if substrate. Geomorphological characterization of more than 60 tafoni in three different Antarctic sites (two coastal and one inland) between 74 and 76 degrees S with sampling of weathering products and salt occurrences are described together with thermal data (on different surfaces) and wind speed recorded in different periods of the year in a selected tafone close to the Italian Antarctic station. The aim of this present study is to provide further information to help understand the processes involved in the growth of tafoni in a cryotic environment, and the relationship of these processes to climate, with particular attention to the thermal regime and the role of wind. The new data presented in this paper suggest that there is no single key factor that drives the tafoni development, although thermal stress seems the most efficient process, particularly if we consider the short-term fluctuations. The data also confirm that other thermal processes, such as freezing-thawing cycles and thermal shock, are not really effective for the development of tafoni in this area. The wind speed measured within the tafoni is half that recorded outside, thus favouring snow accumulation within the tafoni and therefore promoting salt crystallization. On the other hand, the wind effect on the thermal regime within the tafoni seems negligible. While both salt weathering and thermal stress appear active in this cryotic environment, these are azonal processes and are therefore active in other climatic areas where tafoni are widespread (such as the Mediterranean region)

New challenges for tafoni research. A new approach to understand processes and weathering rates

Brandmeier

Kuhlemann

Krumrei

et al. 2010

Cavernous tafoni-type weathering is a common and conspicuous global feature, creating artistic sculptures, which may be relevant for geochemical budgets. Weathering processes and rates are still a matter of discussion. Field evidence in the type locality Corsica revealed no trend of size variability from the coast to subalpine elevations and the aspect of tafoni seems to be governed primarily by the directions of local fault systems and cleavage, and only subordinately by wind directions or the aspect of insulation. REM analysis of fresh tafone chips confirmed mechanical weathering by the crystallization of salts, as conchoidal fracturing of quartz is observed. The salts are only subordinately provided by sea spray, as calcium and sodium sulfates rather than halite dominate even close to the coast. Characteristic element ratios compare well with aerosols from mixed African and European air masses. Sulfates are largely derived from Sahara dust, indicated by their sulfur isotopic composition. Salt crystals form by capillary rise within the rock and subsequent crystallization in micro-cracks and at grain boundaries inside rain-protected overhangs. Siderophile bacteria identified by raster electron microscopy (REM) analysis of tafone debris contribute to accelerated weathering of biotite and tiny sulfide ore minerals. By applying 10 Be-exposure dating, weathering rates of large mature tafone structures were found to be about an order of magnitude higher than those on the exposed top of the affected granite blocks.