A preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment

McGreevy, J.P.

doi:10.1002/esp.3290100509

Cited by 56 publications

(23 citation statements)

References 19 publications

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“…Only Bartrum (1936), McGreevy (1985, Matsukura et al (1989), andRodriguez-Navarro et al (1999) appear to have addressed the origin of the honeycomb pattern itself. Bartrum suggested that the sizes and patterns were the predictable result of random, small depressions on fracture surfaces or bedding planes that grew into mature pits by salt weathering.…”

Section: −0·44mentioning

confidence: 95%

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Origin of honeycombs and related weathering forms in Oligocene Macigno Sandstone, Tuscan coast near Livorno, Italy

McBride

Picard

2004

Earth Surf Processes Landf

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Two types of cavernous-weathering features are exposed in the Oligocene Macigno Sandstone along 5 km of the Tuscan coast south of Livorno, Italy. Honeycomb cells (type 1 features) are typical closely spaced, more or less circular pits of centimetre scale that have been eroded 2 to 6 cm below the general surface of bedding planes or joints. 'Aberrant honeycomb' cells (type 2 features) are highly elongate, polygonal, or irregular flat depressions of decimetre scale surrounded by walls rarely higher than 2 cm, some of which pass into long, free-standing walls or tendrils. Thus, not all type 2 'honeycomb' cells are fully enclosed.We measured the geometry of 551 honeycomb cells and examined various rock properties (microscopic texture and fabric, mineralogy, porosity, permeability, and chemical composition) to isolate factors that control the size, shape, distribution, and pattern of the honeycombs. Our goal was to narrow potential origins of the features and to understand their formation.The ubiquitous occurrence of sea salt in the honeycombs and scanning electron microscope evidence of physical weathering of silicates, especially micas, favours an origin for the honeycombs chiefly by salt weathering. Honeycombs do not form in siltstone, iron-oxide-impregnated sandstone, calcite-cemented concretions, or in case-hardened joints. Thus, salt weathering of type 1 and 2 honeycombs is not effective in very low permeability rocks.We propose for type 1 honeycombs that seawater is drawn into micropores of the sandstone and evolves into selforganized diffusion cells (Turing patterns). Selective evaporation at the stationary nodes of diffusion cells, which form at the same site over time, leads to the precipitation of salt, then grains spall off, and pits are formed. The deepest pits (>40 mm) formed where Turing patterns consistently formed at the same sites. Although the walls are more porous and weathered than the host sandstone, they become selectively case hardened by an unidentified component of low abundance. Initial honeycomb cell shape and gravity locally influenced type 1 honeycomb shapes.We suggest that type 2 honeycombs develop where diffusion-controlled Turing patterns lead to case-hardening along linear trends; gravity and rock fabric are important locally in influencing the orientation of the walls. Only type 2 cells are forming today, suggesting recent environmental changes.Gravity is not a fundamental control on honeycomb shape; in places it is a contributing factor. Pre-existing depressions (quarry tool marks) have strongly influenced honeycomb shape locally.

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Section: −0·44mentioning

confidence: 95%

“…Matsukura et al (1989) suggested that pholad clam borings served as the nucleation site of some cells. McGreevy (1985) said that the reason for the pattern was unknown. Neither Bartrum's (1936), Matsukura et al's (1989), or Rodriguez-Navarro et al's (1999 explanations apply to these Tuscan honeycombs.…”

Section: −0·44mentioning

confidence: 96%

Origin of honeycombs and related weathering forms in Oligocene Macigno Sandstone, Tuscan coast near Livorno, Italy

McBride

Picard

2004

Earth Surf Processes Landf

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“…Honeycomb weathering has long been reported to develop rapidly (Gill, 1981;Mustoe, 1982;Mottershead, 1994;Pye and Mottershead, 1995;Norwick et al, 2001), and it comes as a surprise to recognize that at Pacifi c Northwest sites cavity zones actually represent a retardation of erosion rate relative to adjacent planar surfaces. The apparent scarcity of NaCl residues in honeycombed outcrops (McGreevy, 1985;Young, 1987;Mottershead and Pye, 1994) can perhaps be explained by the seasonal nature of coastal salt weathering: at the present study sites, NaCl crystals were commonly observed in coastal sandstone samples collected during periods of summer dry weather, but not in wet seasons. Honeycomb cavities at a particular location commonly display great morphological diversity, with zones of newly-developed cavities occurring in proximity to areas where other cavity zones are being destroyed.…”

Section: Introductionmentioning

confidence: 73%

“…For supratidal outcrops, salt crystals are typically present within honeycomb cavities during rainfree periods during spring and summer, especially during periods when high tides are accompanied by onshore wind, increasing the amount of seawater deposited as wave splash. This seasonality perhaps explains why some researchers (McGreevy, 1985;Young, 1987;Mottershead and Pye, 1994) failed to detect the presence of salt crystals at coastal sites where honeycomb weathering occurs. Samples collected for …”

Section: Two Weathering Zones: Intertidal and Supratidalmentioning

confidence: 91%

“…The apparent absence of crystallized salts in sandstone from coastal honeycomb zones in Northern Ireland (McGreevy, 1985), Australia (Young, 1987), and greenschist in South Devon, UK (Mottershead and Pye, 1994) caused these investigators to suggest that chemical rather than physical weathering is the dominant force. Observations at Pacifi c Northwest coastal sites provide new information for solving this mystery.…”

Section: Two Weathering Zones: Intertidal and Supratidalmentioning

confidence: 97%

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Biogenic origin of coastal honeycomb weathering

Mustoe

2010

Earth Surf Processes Landf

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Honeycomb weathering occurs in two environments in Late Cretaceous and Eocene sandstone outcrops along the coastlines of south-west Oregon and north-west Washington, USA, and south-west British Columbia, Canada. At these sites honeycomb weathering is found on subhorizontal rock surfaces in the intertidal zone, and on steep faces in the salt spray zone above the mean high tide level. In both environments, cavity development is initiated by salt weathering. In the intertidal zone, cavity shapes and sizes are primarily controlled by wetting/drying cycles, and the rate of development greatly diminishes when cavities reach a critical size where the amount of seawater left by receding tides is so great that evaporation no longer produces saturated solutions. Encrustations of algae or barnacles may also inhibit cavity enlargement. In the supratidal spray zone, honeycomb weathering results from a dynamic balance between the corrosive action of salt and the protective effects of endolithic microbes. Subtle environmental shifts may cause honeycomb cavity patterns to continue to develop, to become stable, or to coalesce to produce a barren surface. Cavity patterns produced by complex interactions between inorganic processes and biologic activity provide a geological model of 'self-organization'. Surface hardening is not a factor in honeycomb formation at these study sites. Salt weathering in coastal environments is an intermittently active process that requires particular wind and tidal conditions to provide a supply of salt water, and temperature and humidity conditions that cause evaporation. Under these conditions, salt residues may be detectable in honeycomb-weathered rock, but absent at other times. Honeycomb weathering can form in only a few decades, but erosion rates are retarded in areas of the rock that contain cavity patterns relative to adjacent non-honeycombed surfaces.

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Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern

Rodríguez-Navarro

Doehne

1999

Earth Surf. Process. Landforms

545

340

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Micro-and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations. Previously unexplained differences are found in crystal morphology, crystallization patterns, kinetics and substrate damage when comparing the growth of mirabilite (Na 2 SO 4 . 10H 2 O) and thenardite (Na 2 SO 4 ) versus halite (NaCl). The crystallization pattern of sodium sulphate was strongly affected by relative humidity (RH), while a lesser RH effect was observed for sodium chloride. Macroscale experiments confirmed that mirabilite (crystallizing at RH>50 per cent) and thenardite (crystallizing at RH<50 per cent) tend to form subflorescence in highly localized areas under conditions of constant RH and temperature. This crystallization pattern was more damaging than that of halite, since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion, a result which contradicts Wellman and Wilson's theoretical model of salt damage. Low RH promoted rapid evaporation of saline solutions and higher supersaturation levels, resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization. At any particular crystallization condition, sodium chloride tended to reach lower supersaturation levels (resulting in the crystallization of isometric crystals) and created negligible damage, while sodium sulphate reached higher supersaturation ratios (resulting in non-equilibrium crystal shapes), resulting in significant damage. ESEM showed no damage from sodium sulphate due to hydration. Instead, after water condensation on thenardite crystals, rapid dissolution followed by precipitation of mirabilite took place, resulting in stone damage by means of crystallization pressure generation.It is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization. These key factors are related to solution properties and evaporation rates, which are constrained by solution composition, environmental conditions, substrate properties, and salt crystallization growth patterns.When combined with a critical review of salt damage literature, these experiments allow the development of a model which explains variations in damage related to combinations of different salts, substrates and environmental conditions.

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A preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment

Cited by 56 publications

References 19 publications

Origin of honeycombs and related weathering forms in Oligocene Macigno Sandstone, Tuscan coast near Livorno, Italy

Origin of honeycombs and related weathering forms in Oligocene Macigno Sandstone, Tuscan coast near Livorno, Italy

Biogenic origin of coastal honeycomb weathering

Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern

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