Hummocky and fluted moraines in part of North-West Scotland

Abstract

This thesis is concerned with the formation and significance of moraines produced c. 11,000-10,000 yrs. B. P. by the glaciers of the Loch Lomond Advance. The moraines have a variety of forms but they have previously been divided into two groups; fluted and hummocky moraines. Fluted moraines have been shown by previous work to be subglacial landforms produced by active ice whereas the majority of hummocky moraines have been attributed to deposition from the surface of stagnant ice.

The methods employed include field mapping and morphological interpretation but the most important data are derived from measuring the particle-size distribution, rock-type composition and other characteristics of the till.

Groups of samples are taken from several groups of fluted moraines. Changes in the properties of the till at different parts of the ridge, between members of a group of ridges, and between ridges and underlying or adjacent till are discussed. The features studied have a variety of sizes but they are generally on a scale that has rarely been described in previous literature, being intermediate between large-scale and small-scale features.

Associations between fluted moraines and hummocky moraines in the field area raised the suspicion that some of the latter may have been formed subglacially. Detailed sampling revealed that all the hummocky moraines studied contain a large proportion of material that was picked up from the valley floors and carried only a short distance during the Loch Lomond Advance. These findings together with other evidence lead to the firm conclusion that the hummocky moraines studied were produced by active ice. This conclusion is accompanied by discussion of the mechanisms by and conditions under which the moraines could have been formed and could have survived. It is suggested that the material was, at least in part, pushed up by the advancing ice front and subsequently passed over by the ice which reworked it to varying degrees.