By Charlie Self
This is an atypical issue of Cave and Karst Science, with the first two contributions having an unusual structure. Despite a wide range of subject matter, there is a distinct "North of England" flavour to this issue.
After a short introduction, this report lists the cave, karst and mining-related papers published by this distinguished cave scientist. Normally such an appreciation follows an obituary, but not in this case. Trevor is still an active speleo-researcher at the age of 90 and publishes several significant papers each year.
This is not so much a paper as a collation of reports on a small region of mostly natural passages at the end of the (mined) Pit Props canal in the Peak-Speedwell cave and mine system. The original mainly descriptive report by Sheldon and Wolstenholme provoked submissions from the other authors, which are combined here.
After a brief introduction by Gunn, the first report (by Ford) outlines the history of exploration before posing three questions (which he calls "enigmas"). The natural passages were mined for lead ore in the late 18th century, before construction of Pit Props canal, so from where did the miners gain access? The second enigma is that the ore-bearing sediments are thought to have been washed in from above, but there is no obvious point of entry. Thirdly, the natural passages lie beneath the probable site of a lost mine, but surviving records show the mine achieving only a third of the necessary depth. Puzzling …. and a spur for further exploration.
The Sheldon and Wolstenholme report is a detailed description of the complex three-dimensional network of excavations opened by the miners in natural passages that were originally sediment-filled. About 50% of these sediments were removed by the miners and a similar amount still remains. A small part of the workings were cut from a pipe-vein deposit in the limestone bedrock. The report includes a plan survey and selected elevation.
The third report (by Shaw) looks at sediments in the cave, particularly in the large Ford's Chamber. Apart from mineral vein-derived clasts and a few chert pebbles, the sediments are mostly sand grains of the minerals quartz and feldspar. A general lack of abrasion on the grains, together with their mineralogy, suggests that they derive from local outcrops of Millstone Grit sandstone, transported from the surface into a pre-existing cavity by sinking streams.
The final report (by Worley) describes the ore mineralisation of this part of the cave/mine complex. The wallrock mineralisation is of the pipe-vein type typical of the Peak District, i.e. formed in pre-existing ancient cavities by circulating mineral-rich solutions. This mineralised ground became a focus for early cave development. The voids so created eventually allowed sediments of surface origin to enter either (a) transported by streams or (b) by solifluction (gravitational slumping) via dolines and the system of open cracks beneath them. Mining activity was largely confined to extraction of these sediments for their mineral content, which included kilogram-sized lumps of galena (lead sulphide). Alteration of the primary ore (galena) to lead carbonate and lead phosphate minerals shows the influence of water of surface origin, as does the presence of secondary manganese minerals.
This is an interesting collection of reports, but there are repetitions and a few inconsistencies which could have been eliminated if this had been presented as one multi-authored paper.
An electric lighting experiment was conducted over a two-year period in Shulgan-Tash (Kapova) Cave, a tourist cave in the South Urals. LED lamps were installed at three sites along the excursion trail to investigate the growth of lampenflora (plants that grow in the vicinity of electric lights). At each site, two lamps were in a fixed position while another two had their orientation changed every 3-4 days. For the duration of the experiment, the lamps were turned on for 4 hours a day, 5 days per week. 280 samples of floor and wall deposits were collected from both experiment and control sites, which were then transferred to cultivation plates in the laboratory.
There was no visible growth of lampenflora in the cave, but cyanobacteria and algae (17 species in total) were detected in 8% of the laboratory samples. No correlation was found between these results and cave temperature, airflow, tourist numbers, artificial illumination or whether the lights were fixed or mobile. However, a positive correlation was found with air humidity. LED lamps provide lighting of low intensity and a specific wavelength, which reduces the risk of lampenflora growth, but this study suggests that extra monitoring is advisable in the more humid parts of tourist caves.
A dye trace was made in typical winter conditions for water sinking at Shep Pot; the water re-appeared at Curry Inlet, from where it entered the Notts II main streamway.
This is a substantial and important paper. The Northern Pennine region is host to most of the maze caves that are found in the UK. A description of some of them was recently given in Cave and Karst Science 39(1), while a survey of the natural maze passages in Devis Hole Mine was published in Cave and Karst Science 39(2). The longest of these maze caves is found in Hudgill Burn Mine and is the subject of this report. The maze was first entered by 19th century lead miners, who surveyed the walking-sized "main thoroughfare" but never explored further than 25 metres from this. The mine was abandoned in the late 19th century, after which the entrance level collapsed. Recent explorations, following the re-opening of the entrance level, have resulted in a total surveyed length of the maze of more than 13 km. The "cave field" (the total area of the maze) is small at only 0.034 km2, giving a "passage density" of 386 km/km2.
The majority of the other Northern Pennine maze caves are also accessed from mines and have a similar exploration history. Though the Hudgill Burn Mine maze has a slightly higher passage density, there are great similarities in both the geology and geomorphology of these mazes. The detailed speleogenetic, mineralogical and geochemical description given here of Hudgill Burn Mine maze is therefore relevant to these other caves.
The Northern Pennine mazes all formed in the Great Limestone, a limestone bed within the mid-Carboniferous Yoredale Group. Unlike the thick sequence of limestone beds (of early Carboniferous age) in which the caves of the Yorkshire Dales formed, the Yoredale Group comprises upwardly repeating cycles of sandstone, limestone and shale. The underlying sandstone acts as an aquifer, while the overlying beds are hydrological barriers. Under these confined artesian conditions, the aquifer can discharge water upwards in a dispersed manner into the soluble limestone to form a (transverse hypogenic) maze cave. The passages so formed have a characteristic suite of dissolution features, termed the "morphological suite of rising flow" (MSRF), which is quite unlike that of usual (epigenic) caves formed by streams sinking from the surface. The natural passages in Hudgill Burn Mine show these MSRF features.
The transverse hypogenic model of cave formation works slowly unless there is some local production of dissolutional aggressiveness. The Hudgill Burn Mine maze is located near mineral veins containing substantial quantities of lead sulphide (galena). However, much of the ore extracted from the mine had changed (by secondary mineralisation) into lead carbonate. Oxidation of sulphide minerals releases sulphuric acid, which greatly enhances the aggressiveness of rising groundwater. There is evidence for this in the maze, where some limestone surfaces are acid-etched while others display efflorescences of calcium sulphate crystals (a reaction product of limestone and sulphuric acid). Oxidation of iron sulphide minerals in the clastic rocks of the underlying aquifer is another potential source of sulphuric acid.
The paper ends with five pages of specialist mineralogy/geochemistry concerning sooty-black manganese oxide deposits that are present on all ceilings and walls. These deposits have a very high zinc content, suggesting that the primary ore veins contained not only lead sulphide but a significant amount of zinc sulphide. In the presence of oxygenated groundwater, this would form zinc ions and sulphuric acid. Manganese is a very common element in the environment and is soluble in anoxic and acidic conditions as Mn2+ ions. When oxidised it becomes the water-insoluble MnO2 (with increased valency and the production of acidity). Manganese oxide minerals are known to be microbially-driven heavy metal scavengers, hence the high zinc content of the deposits in Hudgill Burn Mine maze. MnO2 mineral deposits are common in all types of caves, so this geochemistry section would be of interest to any cave mineralogist.
To end on a lighter tone: a distinctive iron oxide deposit (the "Iron Curtain") was the inspiration for the (Russian/Soviet) naming of different parts of the maze. Students of Geography may be amused to note that a large area of breakdown known as "Stalingrad" lies in the "Siberian Sector" of the maze.
Several small caves may be found at Giggleswick Scar, a fault-line scarp at the southern edge of the Yorkshire Dales caving region. Historically, these caves and rock shelters have been of interest to archaeologists rather than cavers, as they contain Late glacial and Holocene (post-glacial) sediments. The caves are generally small relict phreatic passages, unrelated to the present hydrology.
The authors of this paper suggest that many of these caves formed during the downwasting of an ice sheet that covered the Yorkshire Dales during the Devensian period (last Ice Age). The scoops and rock shelters in the cliff face of Giggleswick Scar North could have been formed by the scraping of ice during the last glacial maximum; the presence of wall scallops suggests that there was flowing meltwater between the ice sheet and the limestone cliff. As the ice sheet melted and became thinner, hilltops emerged from the ice (as nunataks). Ice-dammed lakes would form in summer around these nunataks as the rock warmed, while stress relief (isostatic rebound) opened up joints and bedding planes. At Giggleswick Scar South, this "tectonic inception plus meltwater" resulted in the small phreatic caves seen today.
This paper is highly speculative and even includes a question mark in the title. The idea of de-glacial speleogenesis in the British Isles is intriguing, but the evidence presented here is meagre and open to other interpretations. As the authors themselves state, "if this hypothesis applies, it has wider implications for cave speleogenesis and sedimentation in the Yorkshire Dales." Quite! But the evidence needs to be more convincing. If the authors are willing to look further afield, I would recommend a visit to the west coast of Ireland, to the caves of Oughtdarra township in County Clare.