A multi‐method investigation of temperature, moisture and salt dynamics in tafoni (Tafraoute, Morocco)

Abstract

Despite numerous investigations and theoretical models, tafoni weathering is still not fully understood largely because of limited data available on temperature, moisture and salt regimes. We investigated tafoni developed in granite in the Tafraoute region, Morocco, through an exploratory, two-week multi-method field campaign. Temperatures were measured with iButtons and by means of infrared thermography; moisture distribution and progress were captured with handheld moisture sensors and with drilled-in iButtons. Salts were analysed in drill dust samples from different positions and rock depths.The results derived from very different techniques mutually support one another. Salts and moisture are concentrated near the base of the investigated tafoni, probably due to a saturated pore water body around the base of rock tors. Salts are accumulated close to the rock surface in tafoni, but not on the surrounding rock surfaces. A clear correlation was found between moisture and salt contents. Within a tafone, areas of higher humidity also display increased salt concentration near the surface. The temperature/humidity records allied with ionic analyses suggest that sodium sulfate dominates and is likely to undergo frequent phase changes from thenardite to mirabilite and vice versa. Two pathways of salt transport in and around tafoni are assumed based on the data: infiltration with rainfall on the top and around tors and boulders, and capillary rise from saturated pore water bodies to the surface.

Deterioration processes affecting prehistoric rock art engravings in granite in NW Spain

“…The detachment of blocks is the process that most affects the stability of the petroglyph at the metre scale. Another feature is cave-like decay features known as tafoni, a well-documented morphology of alteration (Groom et al, 2015) whose origin is still a source of controversy: most authors attribute tafoni to the combined action of salts and wind (Huinink et al, 2004;Schnepfleitner et al, 2016), whereas other authors consider the causes to be related to thermal stress processes (Strini et al, 2008;French and Guglielmin, 2000) or to moisture regimes within the rock (Mol and Viles, 2012). These morphologies do not affect the areas of the outcrop with rock engravings, as they are only observed in large blocks already detached from the outcrop.…”

Cool barnacles: Do common biogenic structures enhance or retard rates of deterioration of intertidal rocks and concrete?

“…Holes were drilled into these blocks in areas with and without a cover of barnacles using a hand-held rotary drill. Drilling dust was collected using 'dust bubbles' (Dustbubble Ltd.) which was analysed for chloride and sulphate ions using ion chromatography (Dionex IC DX500) (e.g., Schnepfleitner et al, 2016).…”

Influencia de la temperatura sobre la asimetría de pilancones en ambiente granítico. Aplicación de un modelo de regresión lineal

“…En rocas heterogéneas como los granitos, la insolación genera diferencias de temperatura que actúan a escala de los granos minerales de la roca. Estas diferencias de temperatura producen expansiones y contracciones diferenciales de cada grano mineral según su coeficiente específico de dilatación térmica (Twidale y Corbin, 1963;Smith, 1977;Schnepfleitner et al, 2015), que favorece la desagregación mineral de la superficie rocosa (Gómez-Heras et al, 2006;Gómez-Heras et al, 2008). Ishimaru y Yoshikawa (2000) y Hall y André, (2003) consideran al gradiente térmico uno de los principales procesos de la micro-descamación de superficies graníticas.…”