42 1 School of Earth and Environment, University of Leeds, LS2 9JT, UK. e-mail: P.J.Murphy@leeds.ac.uk 2 Limestone Research Group, Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. e-mail: trevor@marblecaves.org.uk 3 Lower Winskill, Langcliffe, Settle, BD24 9PZ, UK. e-mail: tomlord@daelnet.co.uk 4 5 Holme Park, High Bentham, Lancaster, LA2 7ND, UK. e-mail: john.thorp@tiscali.co.uk Abstract: The prominent Giggleswick Scar at the South Craven Fault extremity of the Carboniferous limestone of the Askrigg Block in North Yorkshire, UK, contains relict phreatic caves whose speleogenesis is enigmatic. This paper examines the local geomorphological evidence and proposes that some, but not necessarily all, karst features along and above the Scar formed after the Last Glacial Maximum. Building on a previous deglacial model for the Yorkshire Dales, it is hypothesized that inception fractures and bedding plane partings were created during isostatic uplift. These were then likely enlarged by dissolution in cold unsaturated meltwater beneath a local flowing deglacial ice- dammed lake that formed initially at an altitude of c.300m, with a catchment area of c. 2km 2 . Rising cupolas outside Gully Cave were probably formed at c. 18ka BP by meltwater flowing up into a moulin within the ice, which continued to be cold-based farther south. As the ice-sheet slowly downwasted, the surface of the lake would have widened and lowered past the newly-formed cave entrances. Some of these were probably enlarged by freeze-thaw and lake-ice push and pull processes. Indeed, the heights of some enlarged entrances correspond to proposed stabilizing lake overflow levels. It is also assumed that the local ice-dammed lake coalesced with the main Settle glacial lake, until a jökulhlaup created a ravine above pre-existing glacial scoops in the limestone cliff. Thereafter, the lake split into two parts on each side of Buckhaw Brow, whilst still inundating the lower caves. If this hypothesis applies, it has wider implications for cave speleogenesis and sedimentation in the Yorkshire Dales. Keywords: Cupola, deglaciation, dissolution, Giggleswick, ice-dammed lake, inception, jökulhlaup, tectonic Received: 07 July 2 014 ; Accepted: 12 February 201 5 © British Cave Research Association 2015 ISSN 1356-191X Cave and Karst Science, Vol.42, No.1, (2015) 42–53 Transactions of the British Cave Research Association The caves of Giggleswick Scar – examples of deglacial speleogenesis? Giggleswick Scar is a prominent cliff line to the north of the B6480 road (the old A65) in North Yorkshire, seen when the valley of Ribblesdale has been crossed upon leaving Settle travelling in a westerly direction (Fig.1). The road skirts the cliff while climbing the steep hill of Buckhaw Brow at 250m AOD. After reaching this crest, the road descends and the cliff line becomes more spectacular. Where the road joins the A65 Settle Bypass (not shown on Figure 1), the cliff becomes more subdued, until the scarp is lost as the A65 takes a turn to the west towards Clapham (Fig.2). It is a classic example of a fault-line scarp along the line of the near-vertical South Craven Fault, which is included in the Geological Conservation Review (Huddart, 2002). This fault defines the southern edge of the Askrigg Block, a major structural unit characterized by platform carbonate deposition in early Carboniferous times. To the south lay the Craven Basin, where deeper water conditions prevailed and deposition of clastic sediment predominated. The South Craven Fault is the southern limit of a heavily faulted area. This is characterised by limestone grasslands whose northern limit is the North Craven Fault, a parallel feature 3km to the north. The area between the two faults is commonly referred to as the Craven Fault Zone. Fault throws are towards the south or southwest and equal about 700m at Giggleswick (Waters and Lowe, 2013, p.24). The local dip of the limestone averages c. 6° towards the southwest. The scarp is formed of Dinantian (Mid Mississippian) carbonates of the Malham Formation, and the lower ground to the south, consisting of Namurian (Late Mississippian to Early Pennsylvanian) sandstones and siltstones of the Millstone Grit Group, is mainly drift covered (Arthurton et al., 1988). The freshness of the topography (Fig.3) suggests that the fault was active during Tertiary times (Nicholson, 1990) and it is possibly still active (Versey, 1948). However, the fault scarp is so prominent because it was periodically eroded by ice throughout the Pleistocene. Evidence to show that ice flowed along the line of the fault scarp is provided by the scarp-parallel orientation of the roches moutonées, which form the rough of Giggleswick Golf Course below the scarp, and other streamlined depositional landforms in the area, including drumlins. These features indicate a late-stage ice flow direction southeastwards, towards the Ribble valley, although to the west of Austwick (which lies some 5km northwest of Buckhaw Brow) the ice flowed westwards (Raistrick, 1930: Fig.2). For convenience and clarity, rock climbers have divided the scarp into two sections. The crags to the northwest of Buckhaw Brow are termed Giggleswick Scar North (Musgrove, 2005; Fig.2); those to the southeast of Buckhaw Brow are termed Giggleswick Scar South (Fig.1). This pragmatic subdivision is retained in this paper, which proposes a preliminary assessment of local speleogenesis. Phillip J MURPHY 1 , Trevor L FAULKNER 2 , Thomas C LORD 3 , and John A THORP 4