Periglacial landforms and environments on mountains in the Northern Highlands of Scotland
Ballantyne, Colin Kerr
This study seeks to establish the characteristics, age and genesis of periglacial landforms; and deposits on mountains in the Northern Highlands of Scotland, and the nature of the environmental conditions under which these features were formed. The study concentrates on investigation of the periglacial. features on three mountain massifs, those of An Teallach, the Fannich-Mountains and Ben Wyvis. A comprehensive classification of upland periglacial features is presented. This classification was employed in detailed mapping of the study areas at scales of 1: 10560 and 1: 10000. These maps allowed analysis of the distributional characteristics of each type of feature in terms of possible controlling variables. Different classes of landform were also surveyed in the field with a view to relating morphology to environment, and the structure of each type was investigated through trenching and sedimentological analysis of constituent material. Measurements were made of present geomorphological activity, and the nature of the present climatic environment was established through meteorological observations on An Teallach. The results of the study indicate that almost all periglacial features were either formed during the Lateglacial period and have long been inactive, or formed during the Flandrian and are active at present. The severe conditions of the Lateglacial cold periods (the period of ice-sheet downwastage and the Loch Lomond Stadial) favoured large-scale frost weathering and the formation of a mantle of shattered detritus on plateaux and on slopes with gradients less than 400, and the rapid accumulation of avalanche-modified talus at the foot of steeper slopes. Even the coarsest detritus was subject to downslope creep, forming sheets and lobes of boulders and debris. Lateglacial frost-sorting produced large-scale patterned ground, and nonsorted patterned ground may have survived in the form of hummocks and relief stripes. Small nivation benches formed in some areas. The severity of the present "maritime" periglacial climate on these mountains is related to high precipitation and strong winds rather than extreme cold. Frost weathering is restricted to granular disintegration and flaking, although rockfall is not infrequent from glacially-steepened rockwalls. Debris-mantled slopes are subject to surficial frost creep and solifluction, the former combining with wind action to produce at least three different types of turf-banked terrace. Wind adtion is also responsible for the formation of deflation surfaces and wind stripes, and for the accumulation of niveoaeolian sand deposits on lee slopes, the last mentioned being subject to active snowpatch erosion. Frost sorting under present conditions is capable of forming sorted circles and stripes that are typically 30-40 cm'in width. Comparison of measured rates of mass-transport suggests that fluvial activity is presently the most effective form of denudationý, followed by rockfall, and that the various forms of masstransport active on high ground operate at rates comparable with (and sometimes greater than) those of similar forms of activity in more severe periglacial environments.