Scottish "hummocky moraine" : its implications for the deglaciation of the North West Highlands during the Younger Dryas or Loch Lomond Stadial
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Stadial
Deglaciation
Allerød oscillation
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ABSTRACT The extent of 64 glaciers that existed in the Lake District during the Loch Lomond Stadial is inferred from end, hummocky and fluted moraines and illustrated by detailed maps. Glacier surfaces are contoured and the equilibrium firn lines of the glaciers are calculated. Firn line altitudes were strongly influenced by snowfall, glacier aspect and the transfer of snow by wind from adjacent high ground. Snowfall was associated mainly with south to southeast winds and the mean direction of winds responsible for snow transfer was probably slightly west of south. It is inferred that mean July temperature at sea-level was slightly below 8°C. Protalus ramparts and other snowbed deposits indicate the former presence of numerous perennial snow beds down to altitudes of 200-300 m although the widespread occurrence of fossil gelifluction sheets and lobes points to large snow-free areas above these altitudes in summer. Fossil valley-wall rock glaciers indicate a mean annual temperature at sea-level no higher than 1°C. During deglaciation the great majority of the small glaciers retreated actively for 100-150 m and then probably decayed in situ , but some, at least, of the larger glaciers were active during much of the time their margins retreated.
Firn
Snow line
Deglaciation
Elevation (ballistics)
Stadial
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The extent of a large mountain icefield that existed in the western Grampians during the Loch Lomond stade has been mapped. The main types of evidence used in establishing the limits comprise moraines, thick drift, fluvioglacial landforms, erratics, ice‐smoothed bedrock, striae, friction cracks and relict periglacial forms. Trimlines on 198 spurs, and various forms of glacial and periglacial evidence on 73 cols and in c . 200 cirques, enable the upper limits and morphology of the icefield to be reconstructed. Abundant striae and friction cracks in many areas enable ice‐flow directions and the surface form of the icefield to be inferred in some detail. The icefield had ice‐shed altitudes of c . 750 m, a maximum width of 80 km and an area over 2,000 km 2 . At least 60 nunataks stood above the icefield, and on its western side outlet glaciers reached the sea and flowed for as much as 28 km along major tidal water lochs.
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Drumlin
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Using evidence provided by hummocky moraines, end moraines, till sheets, drift limits, erratics, meltwater channels, outwash deposits, ice-contact fluvioglacial forms and major periglacial forms, an ice cap (with associated outlet glaciers) that developed in the central Grampians in Late-glacial times is reconstructed using a three-dimensional approach. The former ice surface is contoured at 50 m intervals. The ice mass had an area of nearly 3oo km2, a volume of 32 km3 and an average thickness of about 10 m. Former firn lines are determined and inferences made about contemporary temperatures and the distribution of precipitation. THE area investigated lies in the centre of the Grampian Highlands astride the major east-west watershed (for location see inset, Fig. 2). It is bounded in the west by the Pass of Drumochter glacial breach (D. L. Linton, I951) and in the east by the straight, fault-guided Glen Tilt trench. Part of the area is known as Gaick Forest, but for brevity the whole will be referred to as the Gaick area. The main relief feature is a plateau at 700-930 m that is limited almost everywhere by a sharp 200-450 m descent to lower ground (Fig. I). The plateau is especially well developed in the western half of the area, although it is here cut clean across by a major glacial breach 400 m deep (Loch an Duin breach). The bounding slopes of the plateau are broken by numerous valleys that trend perpendicular to its edge and thus collectively form a radial system. Unrelated to this radial pattern, on the northern edge of the area, is the Glen Feshie glacial breach (Linton, 1949), immediately beyond which are the Cairngorms. Apart from Linton's contributions on glacial breaching and a brief account by J. K. Charlesworth (I955), the only published work on the glaciation of the Gaick area is by G. Barrow et al. (1913). These authors concluded that glacier ice that accumulated in the Gaick area was subsequently largely surrounded and partly overwhelmed by an ice sheet centred in the western Grampians. Local ice later became important again in parts of the area as the exotic ice became less powerful. The limits of local ice were not specified and a readvance was not proposed. BASIC FIELD EVIDENCE
Ice caps
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Deglaciation
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Abstract The aim of this paper is to demonstrate that much of the ‘hummocky moraine’ present within the northern part of the LochLomond Readvance ice cap formerly situated in the North West Scottish Highlands may be interpreted as suites of ice-front moraines deposited during active decay. These landforms can be used to reconstruct ice cap decay, whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions. Evidence has been collected from 10803 airphotographs and from detailed field survey. It is presented at three spatial scales.
Stadial
Deglaciation
Landform
Glacial landform
Reinterpretation
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Abstract Moraines in six cirques in Northern Scotland are shown to be asymmetrically developed, being larger below north‐ or east‐facing valley sides. Moraine asymmetry is strongly correlated with the distribution of free faces in the valleys, a relationship that is interpreted as the result of variation in slope retreat rates. Analysis of clast form and roundness demonstrates that following initial release from bedrock, debris entered both passive high‐level glacial transport and tractive transport at the ice‐bed interface. The importance of glacier velocities and medial moraines on debris flux is discussed. Consideration is also given to the implications of process asymmetry to long term landform development.
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Bedrock
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Snow line
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