Maximum altitude of Late Devensian glaciation on the Isle of Mull and Isle of Jura

• Published in: Scottish Journal of Geology
• Main Author: Ballantyne, Colin Kerr
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1999
• Subjects: LAST ICE-SHEET; NORTHWEST SCOTLAND; FORMER NUNATAKS; HIGH-RESOLUTION; BRITISH-ISLES; RECONSTRUCTION; SOILS; Jura; Mull; Ice Sheet
• Online Access: https://research-portal.st-andrews.ac.uk/en/researchoutput/maximum-altitude-of-late-devensian-glaciation-on-the-isle-of-mull-and-isle-of-jura(7fb9a68f-86f1-4cd3-b72a-d0eb266d15f4).html; https://doi.org/10.1144/sjg35020097; http://www.scopus.com/inward/record.url?scp=0033380978&partnerID=8YFLogxK

Evidence provided by striae, ice-moulded rock, erratics and perched boulders indicates that the last (Late Devensian) ice-sheet reached an altitude exceeding 760 m on Mull and 660 m on Jura. The highest summits on both islands support periglacial blockfields, suggesting that they remained as nunataks above the ice surface. This interpretation is supported by analyses of clay-fraction mineralogy, which shows that gibbsite (a pre-late Devensian weathering product) is widespread in blockfield samples but rare in samples below the inferred limit of glaciation, implying removal by Late Devensian glacial erosion. Maximum ice-sheet altitudes of 760-840 m and 660-700 m are inferred for the Ben Moore massif on Mull and Paps of Jura respectively. Reconstruction of ice-sheet configuration in the Inner Hebrides area suggests that the 900 m ice-surface contour followed the west coast of the mainland, but the altitude evidence is insufficient to constrain the westwards extent of the ice sheet. Inferred ice-surface altitudes and directions of ice movement are incompatible with most theoretical models, and even the 'best fit' model of ice dimensions in this area underestimates maximum ice thickness by greater than or equal to 60 m.