Aberystwyth University Ice flow-unit influence on glacier structure, debris entrainment and transport Jennings, Stephen J. A.; Hambrey, Michael J.; Glasser, Neil F. Published in: Earth Surface Processes and Landforms DOI: 10.1002/esp.3521 Publication date: 2014 Citation for published version (APA): Jennings, S. J. A., Hambrey, M. J., & Glasser, N. F. (2014). Ice flow-unit influence on glacier structure, debris entrainment and transport. Earth Surface Processes and Landforms, 39(10), 1279-1292. https://doi.org/10.1002/esp.3521 General rights Copyright and moral rights for the publications made accessible in the Aberystwyth Research Portal (the Institutional Repository) are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the Aberystwyth Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the Aberystwyth Research Portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. tel: +44 1970 62 2400 email: [email protected] Download date: 26. Sep. 2021 Journal Code Article ID Dispatch: 10.01.14 CE: E S P 3 5 2 1 No. of Pages: 14 ME: 1 EARTH SURFACE PROCESSES AND LANDFORMS 71 2 Earth Surf. Process. Landforms (2014) 72 Copyright © 2013 John Wiley & Sons, Ltd. 3 73 Published online in Wiley Online Library 4 (wileyonlinelibrary.com) DOI: 10.1002/esp.3521 74 5 75 6 76 7 77 8 78 9 Ice flow-unit influence on glacier structure, debris 79 10 80 11 81 12 entrainment and transport 82 13 Stephen J.A. Jennings,* Michael J. Hambrey and Neil F. Glasser 83 14 Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, Ceredigion, SY23 3DB, UK 84 15 85 16 86 Received 2 July 2013; Revised 10 December 2013; Accepted 10 December 2013 17 87 18 *Correspondence to: Stephen J.A. Jennings, Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, Ceredigion, SY23 88 3DB, UK. E-mail: [email protected] 19 89 20 90 21 91 22 92 23 93 24 94 25 95 26 96 27 ABSTRACT: The links between structural glaciology, glacial debris entrainment and transport have been established in a number of 97 28 different glacier settings. Here we document the structural evolution of a temperate Alpine valley glacier (Vadrec del Forno, Switzerland) 98 29 and demonstrate that individual flow units within the glacier have very different structural and debris characteristics. The glacier consists 99 30 of a broad accumulation area with multiple basins feeding a relatively narrow tongue and is formed from six distinct flow units. Each flow 100 31 unit has its own characteristic structural assemblage. Flow units that narrow rapidly down-glacier are dominated by primary stratification 101 32 that has evolved into longitudinal foliation. In contrast, wider flow units preferentially develop an axial planar foliation. Glacier structure 102 33 plays a limited role in the entrainment of debris, which is more strongly influenced by ice-marginal rockfall and avalanche inputs onto the 103 34 glacier surface. However, once entrained, glacier structure controls the reorientation and redistribution of debris within the ice mass. By 104 35 taking a whole-glacier approach to describing glacier structure and debris transport, we conclude that individual flow units are unique 105 36 with regard to structure and debris transfer. Copyright © 2013 John Wiley & Sons, Ltd. 106 37 107 KEYWORDS: Glacier structure; Debris entrainment and transport; Flow unit; Swiss Alps; Vadrec del Forno 38 108 39 109 40 110 41 Introduction Anderson, 2000). Nevertheless, a few studies have addressed 111 42 structural controls on debris transport in contrasting temperate 112 43 The aim of this paper is to investigate the structural evolution of a valley glaciers, notably Austerdalsbreen in Norway and the 113 44 temperate Alpine valley glacier (Vadrec del Forno, Switzerland), Berendon Glacier in the Canadian Rockies (Eyles and 114 45 and to demonstrate that individual glacier flow units exert a Rogerson, 1978), Haut Glacier d’Arolla in Switzerland 115 46 strong control on glacier structure and the entrainment and (Goodsell et al., 2005a, 2005b), Glacier de St. Sorlin in France 116 47 transport of debris. Many sediment–landform associations or (Roberson, 2008), and the lower Fox Glacier in New Zealand 117 48 landsystems preserve evidence of glacier structure, but on the (Appleby et al., 2010). 118 49 whole the relationship with the source glaciers has only been de- Vadrec del Forno differs from the previously studied temper- 119 50 fined in a few cases. Further work is important for reconstructing ate glaciers in having multiple accumulation basins that 120 51 former glacier limits and thermal regime (Evans, 2003). produce converging flow units, each mainly supplied with 121 52 Recent research has focused primarily on the structural blocky granite clasts from precipitous head- and side-walls 122 53 controls of debris transport in high-Arctic polythermal and (Figure 1). Furthermore, years of negative mass balance have F1 123 54 cold-based glaciers. In particular, structural analysis of glacial revealed ice-surface structures in remarkable detail. By apply- 124 55 sediments has been effectively applied to a number of valley ing structurally based sediment analysis techniques to this pre- 125 56 glaciers in Svalbard (Bennett et al., 1996; Hambrey et al., viously unstudied temperate valley glacier, we determine the 126 57 1996, 1999, 2005; Boulton et al., 1999; Hambrey and Glasser, ongoing structural evolution, debris-distribution processes, 127 58 2003b; Hubbard et al., 2004). These studies have highlighted and dynamic history of the glacier, and thereby provide a basis 128 59 the importance of foliation, folding, and thrusting in controlling for comparison with other Alpine valley glacier systems. 129 60 debris transport in polythermal and cold-based glaciers and 130 61 how these processes constrain proglacial landform develop- 131 62 ment. In contrast, there are comparatively few studies of tem- Study Area 132 63 perate valley glaciers. Previous studies have commonly 133 64 regarded debris transport as part of a larger scale glacial system Vadrec del Forno (46˚17′Nto46˚20′N, 9˚40′Eto9˚43′E) is a 134 65 (Drewry, 1972; Boulton and Eyles, 1979; Small, 1987; north-flowing temperate Alpine valley glacier, located in Val 135 66 Kirkbride, 1995; Evans, 2003), or have focused only on the Forno near Passo del Maloja, southeast Switzerland. The gla- 136 67 formation of certain debris-related glacial features (Boulton, cier is approximately 5.3 km in length (Swiss Glacier Monitor- 137 68 1967; Drewry, 1972; Eyles and Rogerson, 1978; Small et al., ing Network, 2013) and consists of a broad accumulation 138 69 1979; Gomez and Small, 1985; Kirkbride and Spedding, 1996; area that comprises two distinct basins feeding a relatively 139 70 140 1 2 S. J. A. JENNINGS ET AL. 71 2 72 3 73 4 74 5 75 6 76 7 77 8 78 9 79 10 80 11 81 12 82 13 83 14 84 15 85 16 86 17 87 18 88 19 89 20 90 21 91 22 92 23 93 24 Figure 1. View of the upper section of Vadrec del Forno from Capanna del Forno. Photograph taken August 2011. 94 25 95 26 96 27 97 28 narrow tongue, with a third joining the tongue halfway along its Field observations 98 29 F2 length (Figure 2). The two main accumulation basins have a Three-dimensional structures were identified in the field 99 30 maximum ice-surface altitude of c. 3200 m a.s.l., with the third according to their dimensions, orientation, and cross-cutting re- 100 31 tributary basin reaching an altitude of 2860 m a.s.l. The glacier lationships, using criteria outlined by Goodsell et al. (2005b). 101 32 snout terminated at 2240 m a.s.l in 2011. Between 1911 and Structures identified on Vadrec del Forno included primary 102 33 2011 the glacier receded 1.9 km, having advanced only for stratification, longitudinal foliation, axial planar foliation, folds, 103 34 one season (1934–1935) since records began (Swiss Glacier and various fracture systems. Three-dimensional measurements 104 35 Monitoring Network, 2013). The glacier terminates as a gently of structures were recorded using a compass/clinometer. The 105 36 sloping convex snout, heavily pitted from both supraglacial following attributes of each structure were recorded: length, 106 37 and subglacial meltwater erosion. The immediate proglacial shape, whether it was open or closed, evidence of displace- 107 38 area is a braid-plain, flanked by uneven rubble slopes of basal ment, debris content and size, ice-crystal size, ice colour, ice- 108 39 and supraglacial debris. The bedrock geology of upper Val crystal shape and alignment, and dip angle and dip orientation. 109 40 Forno and the mountains surrounding the glacier consist almost From these data, the overall glacier structure and its sequential 110 41 entirely of porphyritic granodiorite of Oligocene age (30 Ma), development were determined. 111 42 belonging to the Bregalia – Iorio Intrusive Complex that strad- 112 43 dles the border of Switzerland and Italy (Trommsdorff and 113 44 Connolly, 1996). The rocks are characterized by widely spaced 114 45 joints, but there is no obvious structural feature controlling the Sedimentary facies on the glacier surface 115 46 location of the glacier. 116 Samples of 50 clasts from 37 individual sediment facies were col- 47 117 lected from a variety of locations on and around Vadrec del Forno 48 118 (Figure 2), following the approach of Benn and Ballantyne (1994).