Subglacial meltwater erosion at Loch Treig

Reports of small scale features of glacial erosion by meltwater are rare in Scotland. During the spring of 1996 unusually low water levels in the Loch Treig reservoir revealed an assemblage of exceptionally well-preserved glacial erosion forms sculpted in bedrock, including a suite of meltwater erosion forms. Within the assemblage of landforms at Loch Treig, there is a predominance of forms created by the flow of subglacial meltwater and limited evidence of glacial abrasion. The Loch Treig features are therefore classed as subglacial meltwater erosion forms (s-forms and not p-forms). As such they are probably unique in Scotland. The meltwater forms described from this site include scallops, chutes, chute pools, potholes, and the less specific 'undulose smoothing' of bedrock surfaces. Large groups of 1-1.5 m-diameter scallops are interpreted as phreatic (formed below the water table) in origin. The potholes range from 0.5 m to over 3 m in diameter, with the larger potholes usually occurring in a series with interconnecting chutes. Chutes, chute pools and potholes are interpreted as vadose (formed above the water table) in origin. This interpretation of the suite of features accords well with the established Loch Lomond Stadial events in the area, which suggests that a substantial active glacier was still present in the north end of Glen Treig after the drainage of an ice dammed lake at 260 m in the Spean-Laggan area.