Till and moraine emplacement in a deforming bed surge—an example from a marine environment

Formation and reorientation of structure in the surge‐type glacier Kongsvegen, Svalbard

“…Gripp (1929) first proposed crevasse-filling as a mechanism for incorporating sediment into ice during stagnation and settling of ice on to its substratum. Similar mechanisms were proposed by: Eyles and Rogerson (1978) to explain sediments injected into deep marginal crevasses, followed by redistribution by surging; Sharp (1985b) to explain till ridges in the forefield of the surge-type glacier Eyjabakkajökull, Iceland; by van der Meer (1992) and Boulton et al (1996) to explain the crevasse-intrusion ridges formed on the island of Coraholmen during the surge of Sefstrombreen, Svalbard; and Evans and Rea (1999) to explain sediment Voight (1966). (c) Structures mapped from 1969 aerial photographs.…”

“…During the surge we would expect high porewater pressure within these basal sediments, possible dilatancy and sediment deformation (Blake, 1992;Iverson and Semmens, 1995;Boulton et al, 1996). High basal porewater pressures in a soft-sediment bed may have allowed sediment to be injected from the basal environment into any fracture forming in the ice matrix.…”

Till—as a glacial “tectomict”, its internal architecture, and the development of a “typing” method for till differentiation

“…Since the detection of a depositional style of till formation seems negated by the overwhelming evidence of structures and artefacts, it is reasonable to assert that the material produced by glaciers and ice sheets constitutes a deformable bed (cf. Alley et al, 1987;Boulton, 1996;Engelhardt et al, 1990;Hart et al, 1999), and, therefore, ball subglacial tills from all places and all ages reflect deforming bedsQ (van der Meer et al, 2003(van der Meer et al, , p.1666. Tills should be considered structural sediments much in the manner of cataclastic sediments and rocks (Higgins, 1971;Passchier and Trouw, 1996) and, as such, to differentiate this innovative view of tills a new term must be coined.…”

“…Work especially in Denmark, Poland, the North German Plain, East Anglia in England, as well as the Prairies in North America have described such structures in detail but have, perhaps, been seen as peculiar to specific glaciodynamic regimes and not the norm within tills (see references in Berthelsen, 1978;Brodzikowski and van Loon, 1980;Moran et al, 1980;Hicock and Dreimanis, 1985;Ber, 1987;van Gijssel, 1987;van der Meer, 1987;Van der Wateren, 1987Aber, 1988;Lunkka, 1988;Hart, 1990;Hart and Boulton, 1991;Boulton, 1996;Van der Wateren et al, 2000).…”

Reply: Formation and reorientation of structure in the surge‐type glacier Kongsvegen, Svalbard

“…Many authors have proposed the mechanism to explain sediment entrained in glaciers (e.g. Sharp, 1985;Boulton et al, 1996;Bennett et al, 2000;Ensminger et al, 2001). Furthermore, dewatering has been observed on surge-type glaciers-Bakaninbreen, Svalbard and on Bering and Variegated Glaciers in Alaska, suggesting high basal water pressures.…”