Sir,

Englacial debris in glaciers

In the June 1970 issue of the Journal of Glaciology, Reference Boulton,Boulton (1970) extends his detailed observations from Svalbard to suggest as a generalization “that many polar and sub-polar glaciers, such as those of Svalbard, Greenland, Baffin Island, etc., carry very considerable amounts of englacial debris derived from the glacier bed. . .”.

Over the course of 10 years I have studied, both in the field and on air photographs, glaciers and ice caps throughout the entire region of Baffin Island and I have very little hesitation in concluding that Boulton’s generalization is in fact incorrect, as far as the glaciers and ice caps on Baffin Island are concerned. A majority of the glaciers would have to be classified as “clean” and in many cases, away from the terminal area, the till/ice contact is sharp and there is no evidence of incorporation of the basal till into the ice. Obviously, a large number of glaciers do have a surface-ablation till in the region of their snouts and this grades frequently into one or more ice-cored moraines. However, in such cases, as is well known in the literature, the surficial debris is thin (less than 0.5 m), the amount of debris per unit volume of ice is very small and the ice-cored moraines are, by volume, 95% ice. This in itself still might indicate a moderately rapid supply of debris but one has to take into account at this point the velocity of glacial movement and also the chronology. Studies on a number of glaciers throughout eastern Baffin Island indicate that the ice-cored moraines commonly represent successive events throughout the Neoglacial, that is, the outer ones are dated about 4 000 and the inner ones about 300 years B.P. This, combined with general low velocities, suggests that the debris cover, such as it is, has taken a long time to accumulate.

These observations in no way alter Boulton’s thesis on the Svalbard situation but they do suggest that his generalization is perhaps not valid.