Late Quaternary glaciation and environmental change on St. Kilda, Scotland, and their palaeoclimatic significance zy DONALD zyxwvutsrqponm G. SUTHERLAND, COLIN K. BALLANTYNE AND MICHAEL J. C. WALKER Sutherland, Donald G., Ballantyne, Colin K. zyxwvutsr & Walker, Michael J. C. 19840901: Late Quaternary glaciation and environmental change zyxwvuts on St. Kilda, Scotland, and their palaeoclimatic significance. Boreas, Vol. 13, pp. 261-272. Oslo. ISSN 0300-9483. On Hirta, the largest island of the St. Kilda archipelago near the western edge of the Scottish continental shelf, evidence has been found for four cold periods and one intervening mild period. During the most recent cold period (the Loch Lomond Stadial). two protalus ramparts were formed. Prior to this there occurred two periods of valley glaciation separated by a mild interval during which the local vegetation was dominated by grasses and sedges. For the most recent valley glaciation (= Late Devensian glacial maximum) a mean July temperature of 4°C is inferred. At this time intensive penglacial processes were operative down to present sea level. At some earlier, pre-Devensian, time St. Kilda was invaded by the Scottish ice sheet. Donald G. Sutherland, Departmenf zyxwvuts of Geography, University of Edinburgh, Drummond zyxw Streef, Edin- burgh EH8 9XP, Scotland; Colin K. Ballantyne. Department of Geography, University of St. Andrews, Fife KY16 9AL, Scotland; Michael J. C. Walker, Department of Geography, Sf. David's University College, Lampeter, Dyfed SA48 7ED. Wales; 13fh January, 1983 (revised 16th January, 1984). Born The St. Kilda archipelago (57O49'N; 08'35'W) lies ca. 60 km west of the Outer Hebrides near the edge of the Scottish continental shelf (Fig. 1). The extreme westerly position of the archipelago means that it offers a unique location for placing a limit on the western extent of former Scottish ice sheets, yet little research has hitherto been carried out on its Quaternary history. On the island of Hirta, Cockburn (1935) noted the pres- ence of gneissic boulders and anomalous heavy minerals and tentatively suggested that these may have been transported on to the island by glacier ice from the east. Wager (1953), howev- er, reported several moraines in the Village Bay area of Hirta (Fig. 1) and maintained that St. Kilda had supported only local glaciers. Certain of Wager's supposed moraines were later reinter- preted by Macgregor (1960) as protalus ram- parts. This paper reports the results of detailed inves- tigations of the Quaternary landforms and depos- its on the island of Hirta (Fig. l), which is the largest of the islands that comprise the St. Kilda archipelago. The principal aims of these investi- gations were to determine whether St. Kilda for- merly supported only local glaciers or had been over-run by external ice, and to establish wheth- er terrestrial palaeoenvironmental information for this near-oceanic locality could be used to link evidence from Atlantic deep-sea cores with the terrestrial records of the Hebrides and Scot- tish Mainland. The St. Kilda archipelago The St. Kilda islands are the remnants of a Ter- tiary igneous complex (Cockburn 1935; Harding 1967). The resistant ultrabasic rocks that extend along the west of Hirta (Fig. 2) give rise to a very rugged, craggy topography, but the dolerite sheets of the Mullach Sgar complex, the dolerite, gabbro and breccia of the Glacan Mhor complex and the granophyre that underlies the eastern part of the island have weathered to produce an almost complete soil cover and hills that have much smoother outlines. No in situ sedimentary or metamorphic rocks have been found on the islands, although the rocks of the surrounding continental shelf are believed to consist of Lewi- sian gneiss. The present climate of St. Kilda is milder, slightly less wet but much stormier than that of the Outer Hebrides (Green 1959, 1964). Benbe- cula, the nearest permanent meteorological sta- tion (ca. 60 km E of St. Kilda) experiences a mean July temperature of 13.2"C and a mean annual precipitation of 1,140 mm. zyxw 18 - Boreas 3/84