On the Adhesion of Sediment to Footwear and the Implications for Geoconservation
The fossils at the Mistaken Point UNESCO World Heritage Site represent evidence of the oldest known, large, architecturally complex, life on Earth and are protected by the Government of Newfoundland and Labrador as part of an Ecological Reserve. Following concerns that foot traffic across the fossil surfaces was having a deleterious effect on the geoheritage, visitors were made to wear quilted ‘Bama Sokkets’ starting in 2009—though the efficacy of this management technique has never been tested. Previous studies in the materials sciences have revealed that footwear erosion of rock surfaces is primarily caused by the action of sediment between the foot and the surface; however, these findings have not before been applied to geoconservation research. In this study, we examine the adhesion of sediment to several footwear types. Our experiments reveal that under wet conditions, the ‘Bama Sokkets’ perform poorly in repelling sediment, and as such their use as a geoconservation management tool is discouraged. This study recommends the use of hydrophobic footwear for walking on geoheritage rock surfaces and has led to policy change at the Mistaken Point UNESCO World Heritage Site.
KeywordsGeoconservation Ediacaran Palaeontology UNESCO World Heritage Footwear abrasion
The fossils of MPER have proven amongst the most difficult to decipher in the entire geological record but are crucial to shaping our understanding of the early evolution of large, morphologically complex organisms (Narbonne 2005; Fedonkin et al. 2007). The spectacular impressions of these soft-bodied macroorganisms are dominated by the rangeomorphs, most of which are complex frond-like organisms with self-similar branching (Narbonne 2004).
The scientific importance of the fossils around Mistaken Point was recognised by the Government of Newfoundland and Labrador in 1987, with the establishment of the Mistaken Point Ecological Reserve to encompass an 8.5-km stretch of coastline with an area of 5.7 km2. The Reserve was expanded to its current 17 km of coastline in 2003, to include a number of newly discovered fossil surfaces. After almost a decade of work, MPER was added to the UNESCO World Heritage List on July 17, 2016 (Liu and Matthews 2017).
The Mistaken Point outcrops of the ‘D’ and ‘E’ Surfaces are also the principal locality that tour groups, run by MPER staff, visit to observe the fossil horizons. Visitors must hike for ~ 45 min from the trailhead and, upon reaching the site, walk down off the grassed land surface and across a slope comprising glacial gravels. Before stepping onto the ‘D’ Surface, visitors remove their hiking footwear and put on a pair of ‘Bama Sokkets’, referred to locally ‘bama booties’. The ‘E’ Surface is only accessed from the ‘D’ Surface. Tours operate from mid-May until mid-November (e.g. May 14–November 20 in 2016). Groups typically comprise no more than 25 visitors, with up to four MPER staff accompanying. Access to the site is only through guided tour, or with a research permit.
The wearing of ‘Bama Sokkets’ was brought into effect for all visitors to the ‘D’ and ‘E’ Surfaces in 2008 in response to the legitimate concern that foot traffic may be deleterious to the fossils, in the belief that the soft cloth they are constructed from would prevent damage to the rock surface underfoot. This study seeks to test the efficacy of this geoconservation management technique and provide a scientific rationale for proposing the best kind of footwear from a geoconservation perspective.
A sample of loose surficial sediment was collected from the area commonly used by visitors to change their footwear before stepping into the ‘D’ Surface so as to be representative of the surface walked across in ‘Bama Sokkets’ before stepping onto the fossiliferous ‘D’ Surface. The soil sample was collected on November 4, 2016, and was damp at the time of collection. Data from the nearby Cape Race meteorological station shows the area to have received rain on every previous day since October 29, 2016. A total of 3.14 kg of sample was collected and transported (under permit) to the lab in sealed bag to prevent loss of moisture.
An experiment was designed to test the amount of sediment that would adhere to the base of different footwear types. This is based on the precept that the conveyance of surface sediment, an abrasive substance, on the sole of footwear would be detrimental to fossil protection. By identifying the footwear with the least sediment adhesion, we aim to determine a protocol with the best geoconservation outcomes.
Following the testing using damp sediment, the soil sample was dried in an oven at 80 °C for 24 h. The sample was weighed and the moisture loss calculated. Testing was then repeated using the dried sediment. It is noted that some net loss of moisture could have occurred during the experiment itself, and also some mass loss of sediment may also have occurred—though every effort was made to return adhered sediment to the sample tray after each analysis.
‘Bama Sokkets’—designed as thermal insulation to be worn within shoes. They are constructed of an inner layer of polyester or acrylic fleece, with an exterior lining of cotton. These two layers are held together by stitching throughout the design. Two qualitative ‘life stages’ of the ‘Bama Sokkets’ were tested: ‘nearly new bama’ (Fig. 4a) that had only recently entered into use at MPER and ‘old bama’ (Fig. 4b, c), which constituted a pair that had been retired from use due to degradation of the cotton outer layer at the sole.
Walking socks—the design used for the experiment was the Heat Holder Men’s Original. They comprise 91% acrylic, 5% nylon, 3% polyester, and 1% elastane (Fig. 4d).
Sports socks—the design used comprised the following materials: 67% cotton, 22% polyamide, 9% polyester, and 2% elastane (Fig. 4e).
Shoe—the design comprised a standard black leather shoe, with a rubber sole and boot-like tread (Fig. 4f). Such footwear was only used before the site was formally recognised for its scientific value and the need for protection.
The initial mass of the sediment when wet was 3.1497 kg, which decreased by 0.0939 kg when dried. This implies that the sediment used for the experiment held about 3% moisture content at the time of experimentation.
During the process of securing the inscription of Mistaken Point as a UNESCO World Heritage Site, concern had been raised about the effects of foot traffic on the fossil surfaces. This concern is heightened by the recognition that inscription has led to a dramatic increase in the number of people taking the guided tour to the ‘D’ and ‘E’ Surfaces (MPER manager pers. comm.).
Two-body abrasion: where either the footwear has a rough lower surface or abrasive particles are tightly fixed to the footwear
Three-body abrasion: where abrasive particles are loose and free to shift between the footwear and the bedding surface
In three-body abrasion, two surfaces slide past each other, interspersed by third bodies—usually particles that slide or roll during motion (Hutchings and Shipway 2017). The friction between the moving third bodies and the flooring surface causes a polishing effect, abrading the surface (Frick 1969). The main cause of wear on stone floors, and by analogy geological bedding surfaces, is from three-body abrasion (Yılmaz et al. 2017).
While short-term events involving two-body abrasion can be highly destructive (e.g. when a stone is stuck in the tread of a shoe which then scratches a flooring surface), three-body abrasion is the dominant form of abrasion underfoot, as it occurs much more consistently and is less obvious to the walker.
Reduce the amount of sediment on the surface before visitors arrive
Reduce the amount of sediment brought onto the surface by visitors
Reduce the ability of footwear to transport sediment when on the surface
If we accept three-body abrasion is the dominant wear process, and this is controlled by the availability of abrasive particles, aims 2 and 3 can be met by requiring footwear with minimal sediment adhesion to be worn before walking on the Mistaken Point surfaces.
While all the tested footwear types were found to transport a similar amount of dry sediment, significant differences were observed when the sediment was wet. This observation is of importance since during the period when tours were in operation in 2016, the nearby Cape Race weather station recorded a mean daily rainfall of 3.4 mm, and some kind of precipitation was recorded on 40% of days.
While it was found that a shoe transports the least amount of wet sediment relative to the other footwear types, there is an enhanced risk that large abrasive clasts could lodge in the tread, causing the less-common, but highly damaging, two-body abrasion, potentially producing pock marks and scratches. Shoes with any sole capable of having sediment lodged in the tread are therefore ruled out as suitable footwear on protected geological surfaces.
The type of footwear that was most efficient at transporting sediment—and therefore most likely to cause abrasion—was the ‘Bama Sokkets’. Old bamas were found to transport slightly less sediment than nearly new bamas when wet. This was counter to our expectations, since the extra texture at the frayed edges of the cloth in the old bamas (Fig. 4c) was thought to provide more capacity to carry sediment than the smoother new bamas. Detailed empirical observation of the soles of the ‘Bama Sokkets’ after the wet sediment tests revealed that, in areas where the outer layer of blue cotton cloth had been worn away, less sediment adhered to the sole (Fig. 4b, c).
Table showing the composition of different materials comprising the footwear types tested and their hydrophobic or hydrophilic properties
Natural fibre from Gossypium plant
Synthetic polymer based on polyamides
Polymers of natural isoprene
The sports sock tested was composed predominantly of hydrophilic cotton, with some hydrophobic fibres, and was found to transport significantly more sediment in wet conditions than when dry. In contrast, the walking sock tested—despite its coarser weave relative to the sports sock—was found to transport less sediment. While the amount of wet sediment transported by the walking sock was more than during experiments involving dry sediment, this increase was much smaller than in either the ‘Bama Sokkets’ or the sports sock and is likely explained by the lack of hydrophilic fibres in the walking sock.
From the experimental evidence presented herein, it is determined that the major control on sediment adherence to footwear is the material that it has been constructed from. Footwear made from hydrophobic fibres is less likely to transport damp sediment and so will reduce three-body abrasion on rock surfaces, when compared to hydrophilic alternatives. These results have led to a change of policy at MPER, and from 2019, the Government of Newfoundland and Labrador will be discontinuing the use of ‘Bama Sokkets’ and will replace them with a hydrophobic alternative.
Since 2008, visitors to the most spectacular fossil surfaces within the Mistaken Point Ecological Reserve have had to wear ‘Bama Sokkets’ when walking on these internationally significant geosites. This footwear type is made of acrylic/polyester fleece, covered in an outer layer of cotton textile. Evidence presented herein suggests this cotton layer is particularly prone to transporting damp sediment, which is significant as the ability of a footwear type to transport sediment on its sole is a major control on the amount of abrasion that will occur between the sole and an underlying fossil surface.
While the decision to begin using ‘Bama Sokkets’ was well intentioned, and in keeping with the best practice at the time, these new data show that a footwear type constructed of hydrophobic fibres would have produced better geoconservation outcomes by decreasing instances of three-body abrasion on the fossil surfaces. The removal of footwear remains an essential management protocol at the site, and there is anecdotal evidence to suggest that making visitors wear a particular piece of footwear increases awareness of how actions may adversely affect the site. Further research is required to understand the natural erosional processes at the site and to quantify the possible abrasion caused by foot traffic.
Many important geosites require researchers and geotourists to walk across rock surfaces to study and observe geoheritage. The results of this study are therefore pertinent not only to the geoconservation of Ediacaran fossil sites in Newfoundland, but also to other bedding planes hosted geoheritage worldwide, such as dinosaur trackways and certain fossil lagerstätte.
Permits for research within the Mistaken Point Ecological Reserve are required and available from the Department of Fisheries and Land Resources. The thoughtful comments of two reviewers greatly assisted in improving this manuscript. The continued assistance of the communities of the Southern Shore, Newfoundland, and the staff at MPER is gratefully acknowledged, as is the support of the Legendary Coasts Destination Management Organisation.
This research was supported by funding from MITACS and the Department of Fisheries and Land Resources, Government of Newfoundland and Labrador, as well as NSERC DG funding to Prof. Duncan McIlroy.
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