A characterisation of debris transport and depositional landforms at a humid-temperate debris-covered glacier: Belvedere Glacier, Italy

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1 A characterisation of debris transport and depositional landforms at a humid-temperate debris-covered glacier: Belvedere Glacier, Italy Alex Neen M.Sc. Glaciology Fieldwork supported by donations from the Jeremy Willson Charitable Trust (through the RGS-IBG) and IGES, Aberystwyth University

2 Study area: Belvedere Glacier Surrounded by numerous large peaks including Monte Rosa (altitude 4634m) with its steep east face ( m a.s.l.) The east face composes of firn-fields, steep hanging glaciers, icefall and rockfall feeding the debris covered tongue of Belvedere glacier Characterised by numerous periods of advance and thickening (e.g. The surge of ) in contrast to the current Alps theme of retreating glaciers. Previous work focuses on mass balance, volume and velocity fluctuations and the instability of the Monte Rosa east face at the expensive of in depth sedimentological studies (e.g. Haerberli, et al., 2002; Diolaiuti et al., 2003; Kaab et al., 2004)

3 Debris transport by glaciers Glacial valley systems have two principle sources: Rockwalls and subaerial slopes, and the glacier bed (Iverson, 1995) Subglacial material is generated by plucking, abraded bedrock and over-ridden sediments while mass movement supplies subaerial sources (Drewry, 1986; Benn and Evans, 1998; Benn and Evans, 2004) Glacial transport is passive or active (Boulton, 1978) Temperate and alpine valley glaciers are dominated by passive transport (Benn et al., 2003) To characterise supraglacial and englacial debris as passive is an oversimplification e.g. Ablation leading to meltwater reworking (Owen et al., 2003)

4 Important role played by structural glaciology and meltwater - Subglacial and englacial conduits emerge at the surface (Benn et al., 2003; Hambrey and Ehrmann, 2004) - Rockfall buried englacially and at the surface can be reworked fluvially (Owen, 1994; Kirkbride and Spedding, 1996) - Transition from a steep icefall to an overdeepening results in a switch from subglacial to englacial drainage and cavity formation elevating basal ice into high level transport (Hooke, 1991; Kirkbride, 1995; Spedding, 2000) - Entrainment of basal debris related to thrusting mechanisms and shear zones represented by higher quantities of actively worked clasts in the frontal region of the glacier. Attributed to longitudinal compression at temperate glaciers (Näslund and Hassinen, 1996; Benn and Evans, 1998; Owen et al., 2003; Hambrey and Ehrmann, 2004; Hambrey et al., 2008)

5 Debris in the glacial system can be subdivided into separate systems such as debris in transport, debris deposited and debris reworked following deposition (e.g. Hambrey and Ehrmann, 2004) Glaciated valley landsystem : large rockfall source supplying supraglacial debris while sedimentological evidence demonstrates some is elevated from the bed (e.g. Benn et al., 2003; Hambrey et al., 2008) Supraglacial debris cover increases in thickness downglacier and with distance from the centreline (e.g. Nakawo et al., 1986; Owen et al., 2003; Kellerer-Pirklbauer, 2008) -Relates to the distribution of debris sources and transport paths, importance of..localised englacial and subglacial debris deposited at surface and levels of fluvial..reworking activity (Benn and Evans, 1998; Kellerer-Pirklbauer, 2008) Margins of glacier characterised by large moraine complexes enabling sedimentological analysis of relict transport paths

6 Aims and objectives Assess whether debris is transported by passive supraglacial processes or whether active debris transport is significant at a debris-covered glacier in the Alps A Comparison of debris: (a) currently in supragacial transport (b) deposited by the glacier (c) reworked after deposition (proglacial stream) (d) reworked during transport (supraglacial stream) To determine whether debris thickness increases with distance downglacier and the centreline or whether the east face source at the glacier headwall ensures a constant thickness with no basal or englacial entrainment To characterise a debris-covered glacier system in the European Alps using sedimentological and gemorphological (including geomorphological mapping) evidence enabling a comparison with debris-covered glaciers in other regions e.g. New Zealand and the Himalayas

7 Methods Sedimentological analysis Sedimentological description (e.g. particle size, sorting, % gravel) enabling the determination of distinguishable lithofacies using the classification of poorly sorted sediments modified from Moncrieff (1989) by Hambrey (1994) fine material - indicates basal transport Clast roundness of 50 clasts per site based on the Powers roundness scale (1953). High RA indicates passive transport while a low RA implies basal transport or fluvial reworking (Benn and Ballantyne, 1994) Clast shape of 50 clasts per site by initially...measuring the a-b-c axis and determination of...shape by use of tri-plots (Graham and Midgley, 2000) - high c/a axial ratios indicative of active transport represented...in a block form - unmodified frost-weathered debris is likely to be slabby and... elongate (Benn and Ballantyne, 1994) Clast texture and surface features e.g. Striae Slabs c : a Blocks (a - b) / (a - c) b : a Elongates

8 Debris thickness Measured by removing debris down to the ice surface Thickness measurements were taken at every sedimentological site in addition to two concentrated transverse transects Geomorphological mapping A combination of desk-based and fieldwork reconnaissance with glacial boundaries delineated by the use of ASTER imagery which was complemented by detailed mapping and ground-thruthing in the field Site Subsurface site Debris thickness only Debris thickness transect

9 Glacial setting Debris transport Environment (and number of sites) Supraglacial (13) Supraglacial ridge (2) Supraglacial (subsurface) (3) Lithofacies (and number of sites) Sandy boulder gravel (5) Boulder gravel (7) Angular boulder gravel (1) Gravelly sand (2) Muddy gravelly sand (3) Results Sorting Percentage Dominant clast roundness Dominant clast shape RA/c₄₀ index % striated clasts Gravel Sand Mud 0 Poorly sorted A SR,(SA) Slabby/elongat e Moderate 0 Moderately VA-SR, (SA) Variable Moderate- 0 sorted High Poorly sorted VA-SA, (A) Variable High 0 Moderately A-SR, (SR) Variable Moderate 0 sorted Poorly sorted A-SR, (SA) Blocky Moderate 0 Stream-worked supraglacial (2) Muddy sandy boulder gravel (1) Muddy sandy pebble gravel (1) Moderately sorted Moderately sorted SA-SR, (SR) Variable Low A-SR, (SA) Blocky/Slabby Low- Moderate 0 Debris deposited Poorly sorted SA-SR Blocky Lowmoderate 0 Moderately SA-R, (SR) Variable Low 0 sorted Postdepositional reworking Lateral/Lateralterminal moraine (11) Proglacial glaciofluvial (3) Valley side debris fan (1) Sandy boulder gravel (5) Sandy diamicton(6) Sandy boulder gravel (2) Sandy cobble gravel (1) Gravelly sand (1) Poorly sorted SA-SR Blocky Lowmoderate Well sorted SR-R, (SR) Blocky/Slabby Low 0 Moderately sorted SA-SR, (SA) Variable Low 0 0 (some boulders)

10 C₄₀ = 88 C₄₀ = 52 C₄₀ = 34 C₄₀ = 24 Supraglacial: sandy boulder gravel Supraglacial: Gravelly sand Glacial deposit: Sandy diamicton Reworked deposit: Sandy boulder gravel Supraglacial : Angular boulder gravel C₄₀ = 88

12 Debris in transport Interpretation Facies environment interpretation Abundance Sandy boulder Supraglacial debris Rockfall, scree, basally ***** gravel surface entrained debris Boulder gravel Supraglacial debris surface Rockfall, scree, fluvially reworked debris ***** ** Angular boulder gravel Supraglacial debris surface Rockfall (possible catastrophic), scree * Gravelly sand Supraglacial ridge Basally entrained debris, limited Rockfall and scree Muddy gravelly sand Supraglacial debris subsurface Rockfall, scree, basally entrained debris ** *** Muddy sandy boulder gravel Supraglacial stream Supraglacial fluvial reworking * Muddy sandy pebble gravel Supraglacial stream Supraglacial fluvial reworking * Debris deposited Sandy boulder gravel Large/Small lateral moraine ridge Basally transported debris, Rockfall, Scree ***** Postdepositional reworking Sandy diamicton Sandy boulder gravel Sandy cobble gravel Large lateral moraine ridge, small lateral moraine ridge Proglacial glaciofluvial Proglacial glaciofluvial Basally transported debris, Rockfall, Scree Proglacial fluvial reworking Proglacial fluvial reworking ****** ** * Gravelly sand Valley side debris fan Fluvial reworking of rockfall or past glacial deposits *

13 Debris thickness (cm) Debrs thickness (cm) Debris thickness R² = Distance from terminus (m) Distance along transect (m)

14 Geomorphology Large lateral moraines are the dominant feature surrounding the whole glacier margin reflects advance and thickening followed by stagnation and downwasting rather than retreat (Boulton and Eyles, 1979; Kirkbride, 1995; Benn et al., 2003) High levels of mass movement and flanked by ablation valleys - Similar to Karakoram and the Himalayas system described by Owen (1994) Parallel to smaller moraine ridge, closer to the ice margin Formed as the glacier stabilised into a new position or underwent rapid thickening (Small, 1983; Benn and Evans, 1998) Limited proglacial area and fluvial imprint

15 Further discussion and conclusions Geomorphological mapping to be completed to highlight dominance of moraine networks and strong glacial imprint landsystem similar to that of Himalayan debris-covered glaciers Full characterisation required A reasonable proportion of debris currently in supraglacial transport has been actively transported Higher quantities are located in moraine deposits Spatial trends in sedimentological data?

University in Prague, Albertov 6, 128 43 Praha 2, Czech Republic. Life Sciences, Kamýcká 1176, 165 21 Praha 6 Suchdol, Czech Republic

University in Prague, Albertov 6, 128 43 Praha 2, Czech Republic. Life Sciences, Kamýcká 1176, 165 21 Praha 6 Suchdol, Czech Republic CZECH POLAR REPORTS 3 (2): 107-129, 2013 New methods to reconstruct clast transport history in different glacial sedimentary environments: Case study for Old Red sandstone clasts from polythermal Hørbyebreen