Glacier recession, glacial sediment export and the morphodynamics of proglacial forefields

Supported by the Swiss National Science Foundation, 2020-2024

PhD students: Matt Jenkin and Davide Mancini

Research Technician: Floreana Miesen

  1. Introduction

Proglacial margins, exposed following glacier and ice sheet retreat, have been described as one of the most rapidly changing landscapes on Earth. In the Swiss and Austrian Alps alone, c. 930 km2 of proglacial margins have formed since the Little Ice Age (Carrivick et al. 2018). Our knowledge of the geomorphic processes that follow glacier retreat is well-developed (McColl and Draebing, 2019; Porter et al. 2019). Deglaciation implies debuttressing (Cossart et al. 2008) such that previously immobile sediment can be more readily mobilised. It leads to (1) increased rockfalls (Ravanel and Deline, 2011; Heckmann et al. 2016); (2) moraine evolution through erosion (Curry et al. 2006; Lane et al. 2017); (3) dead ice melt-out (Bosson et al. 2015); (4) paraglacial landsliding (Hugenholtz et al. 2008; Cossart et al. 2013); (5) debris flow formation (Haas et al 2012); and (6) rock glacier formation/response (Käab et al., 2007; Micheletti et al. 2015). The paraglacial model (Church and Ryder, 1972) argues for peak geomorphic activity immediately after deglaciation then declining due to sediment exhaustion and negative feedbacks (e.g. vegetation development; Eichel et al.2015).
A crucial element of proglacial margins that can develop following deglaciation is the proglacial forefield (Figure 1). If valley slope is low enough to prevent deep river incision, there is sufficient lateral accommodation space for river migration and there is no natural or artificial overdeepening and proglacial lake formation a morphodynamically active proglacial alluvial plain, or “forefield” may form (figure 1). These latter are of crucial importance as they buffer valley side-slope hazards (rockfalls, debris flows,…; Oppikofer et al., 2008) and they can potentially act as filter for sediment exported from glaciers, and hence on downstream sediment yield from glaciated basins.

Figure 1. The proglacial forefield of the Otemma Glacier South-West Switzerland

Sediment mobilisation processes have been largely described (e.g. Church and Ryder, 1972; Mercier et al., 2008) and quantified (archival imagery, sediment budgets, sediment cascades; e.g. Warburton, 1990; Staines et al., 2015; Lane et al., 2017). The effects of glacier thinning and recession on glacier erosion are increasingly well known: a thinning glacier should deform and so erode more slowly; but the enhanced melt (“meltwater dividend”; Collins, 2008) may encourage glacier acceleration and sliding-enhanced erosion (Koppes et al. 2009). However, the relationship between climate warming and sediment yield in deglaciating basins remains highly uncertain notably (1) how glaciers evacuate sediment through their marginal zone and into the forefield; and (2) the role that forefields play in filtering the flux of evacuated sediment (Heckman and Morche, 2019; Porter et al 2019). These observations lead to the core aim of this proposal: undertake the first, coupled study of the relationship between subglacial sediment export, proglacial forefield morphodynamics and sediment flux to understand the role of proglacial margins in filtering sediment export from retreating temperate Alpine glaciers. The study areas for this project are located in the Swiss Alps (Wallis), and more in particular on the proglacial forefields of the Glacier d’Otemma and the Gornergletscher (Figure 1).

  1. Subglacial sediment export (PhD candidate to be appointed)

Controls on the rate of sediment export by a glacier to its forefield are poorly known (Koppes and Montgomery, 2009). Export is a function of the ability of a glacier both to erode (abrasion, plucking) and to transport sediment to the glacier margin. It is assumed that erosion at a glacier bed translates directly into transfer of eroded sediment to the glacier outlet and that erosion continues only if subglacial channels are capable of evacuating eroded sediment (Riihimaki et al. 2005). That said, observations suggest that sediment export is variable over a number of timescales: (1) within-daily, bedload transport can be locally capacity limited due to diurnal discharge minima (Perolo et al. 2019); and (2) seasonally, sediment export declines through the melt-season, attributed to the progressive evacuation of winter-eroded sediment (Riihimaki et al. 2005; Gimbert et al. 2016).

Sediment export rates and volumes from retreating glaciers are studied coupling three methods. First, bedload and suspended sediment load are measured directly in front of the snout of the glacier to determine variation in sediment export rates. Second, repeated GPR surveys are undertake to establish the topography, but also the dynamics, of the subglacial channels in the snout margin zone. Third, particle tracking method, injecting pit-tagged sediments into crevasses and moulins, is used to quantify storage duration and transfer delays in space and time.

  1. Proglacial forefield dynamics following glacier retreat (PhD student Davide Mancini)

Forefield response to deglaciation is a function of the ratio of sediment supply to sediment transport capacity. The dividend of increased runoff during glacier retreat (Collins, 2008) may increase sediment transport capacity dramatically (Lane et al. 2017) but morphodynamic response then depends on whether or not there is concomitant increase in glacial sediment export. With glacier recession, there is evidence (de Winter et al. 2012; Cordier et al. 2017) that supply does not keep up with capacity. This is reflected in incision in front of retreating glacier margins, which provides sediment necessary for downstream aggradation, aided by reductions in downstream bed slope (incision-aggradation, Marren, 2002; Beylich et al. 2009). It is also reflected in terrace formation (Marren and Toomath, 2013). Over seasonal to decadal time scales, formation of proglacial lakes has been shown to reduce gravel supply (Bogen et al. 2015) and promote downstream incision-aggradation (Chew and Ashmore, 2001); but conditions have been observed where supply can keep up with capacity increases as aggradation following glacier retreat is observed throughout the forefield (Curran et al. 2017). Thus, understanding how forefields respond to climate retreat must consider the effects of both the meltwater dividend and glacier sediment export, with reference to large-scale topographic forcing (e.g. lateral accommodation space and valley slope) within the forefield.

Proglacial margin response to glacial retreat is studied coupling sediment budget technique (analysis of continuous suspended sediment and bedload discharges at specific proglacial stream spots) with remote sensing analysis of surficial geomorphological changes (repeated DEMs of differencing starting from UAV imagery; figure 3) through time. In addition, in collaboration with Prof. A. Nicholas (Exeter University), collected data will be used to develop the HSTAR model to simulate how different sediment supply rates impact morphodynamics and sediment flux downstream.

  1. References

Beylich, A., Laute, K., Liermann, S., Hansen, L., Burki, V., Vatne, G., Fredin, O., Gintz, D., Berthling, I. (2009).            Subrecent sediment dynamics and sediment budget of the braided sandur system at Sandane,  Erdalen (Nordfjord, Western Norway), Norsk Geografisk Tidsskrift, 63, 123–131.

Bogen, J., Xu, M., Kennie, P. (2015). The impact of pro-glacial lakes on downstream sediment delivery in Norway, Earth Surf. Process. Landf., 40, 942–52.

Bosson, J-B., Deline, P., Bodin, X., Schoeneich, P., Baron, L., Gardent, M., Lambie,l C. (2015). The influence of ground ice distribution on geomorphic dynamics since the Little Ice Age in proglacial areas of two cirque glacier systems, Earth Surf. Process. Landf., 40, 666–680.

Carrivick, J.L., Heckmann, T., Turner, A., Fischer, M. (2018). An assessment of landform composition and      functioning with the first proglacial systems dataset of the central European Alps, Geomorphology,    321, 117-28.

Chew, L.C., Ashmore, P.E. (2001). Channel adjustment and a test of rational regime theory in a proglacial braided stream, Geomorphology, 37, 43–63.

Church, M., Ryder, J.M. (1972). Paraglacial Sedimentation: A Consideration of Fluvial Processes Conditioned by Glaciation Geological, Society of America Bulletin, 83, 30-59.

Collins, D. (2008). Climatic warming, glacier recession and runoff from Alpine basins after the Little Ice  Age maximum, Ann. Glaciol., 48, 119–124.

Cordier, S., Adamson, K., Delmas, M., Calvet, M., Harmand D. (2017). Of ice and water: Quaternary fluvial     response to glacial forcing, Quaternary Science Reviews, 166, 57–73.

Cossart, E., Braucher, R., Fort, M., Bourlès, D.L., Carcaillet, J. (2008). Slope instability in relation to glacial     debuttressing in alpine areas (Upper Durance catchment, southeastern France): evidence from field data and 10Be cosmic ray exposure ages, Geomorphology, 95, 3–26.

Cossart, E., Mercier, D., Decaulne, A., Feuillet, T. (2013). An overview of the consequences of paraglacial      landsliding on deglaciated mountain slopes: typology, timing and contribution to cascading fluxes, Quaternaire, 24 13–24.

Curran, J.H., Loso, M.G., Williams, H.B. (2017). Glacial conditioning of stream position and flooding in the braid plain of the Exit Glacier foreland, Alaska, Geomorphology, 293, 272–88.

Curry, A.M., Cleasby, V., Zukowskyj, P. (2006). Paraglacial response of steep, sediment-mantled slopes to    post-Little Ice Age glacier recession in the central Swiss Alps, J. Quat. Sci., 21, 211–225.

De Winter, I.L., Storms, J.E.A., Overeem, I. (2012). Numerical modeling of glacial sediment production and    transport during deglaciation, Geomorphology, 167–168, 102–14

Eichel, J., Corenblit, D., Dikau, R. (2015). Conditions for feedbacks between geomorphic and vegetation         dynamics on lateral moraine slopes: a biogeomorphic feedback window, Earth Surf. Process. Landf.,  41, 406–419.

Gimbert, F., Tsai, V.C., Amundson, J.M., Bartholomaus, T.C., Walter, J.I. (2016) Subseasonal changes observed in subglacial channel pressure, size, and sediment transport, Geophysical Research Letters, 43, 3786-94.

Haas, F., Heckmann, T., Hilger, L., Becht, M. (2012). Quantification and modelling of debris flows in the          Proglacial Area of the Gepatschferner/Austria using ground-based LIDAR, IAHS Publ., 356, 293–302.

Heckmann, T., Hilger, L., Vehling, L., Becht, M. (2016). Integrating field measurements, a geomorphological map and stochastic modelling to estimate the spatially distributed rockfall sediment budget of the Upper Kaunertal, Austrian Central Alps, Geomorphology, 260, 16–31.

Heckmann, T., Morche, D. (2019). Geomorphology of proglacial systems: landform and sediment dynamics    in recently deglaciated Alpine landscapes, Springer.

Hugenholtz, C., Moorman, B., Barlow, J., Wainstein, P. (2008). Large-scale moraine deformation at the           Athabasca Glacier, Jasper National Park, Alberta, Canada, Landslides, 5, 251–260.

Kääb, A., Frauenfelder, R., Roer, I. (2007). On the response of rock glacier creep to surface temperature increase, Glob. Planet Change, 56, 172–187.

Koppes, M., Hallet, B., Anderson J. (2009). Synchronous acceleration of ice loss and glacial erosion, Glaciar Marinelli, Chilean Tierra del Fuego, Journal of Glaciology, 55, 207-20.

Koppes, M.N., Montgomery, D.R. (2009). The relative efficacy of fluvial and glacial erosion over modern to     orogenic timescales, Nature Geoscience, 2, 644-647.

Lane, S.N., Bakker, M., Gabbud, C., Micheletti, N., Saugy, J.-N. (2017). Sediment export, transient landscape response and catchment-scale connectivity following rapid climate warming and Alpine glacier recession, Geomorphology, 277, 210-27.

Marren, P.M. (2002). Glacier margin fluctuations, Skaftafellsjökull, Iceland: Implications for sandur evolution, Boreas, 31, 75–81.

Marren, P.M., Toomath, S.C. (2013). Fluvial adjustments in response to glacier retreat: Skaftafellsjökull,          Iceland, Boreas, 42, 57–70.

McColl, S.T., Draebing, D. (2019). Rock Slope Instability in the Proglacial Zone: State of the Art Chapter 8 in Heckmann, T. and Morche, D. (Eds.), Geomorphology of proglacial systems: landform and sediment dynamics in recently deglaciated Alpine landscapes, Springer.

Mercier, D. (2008). Paraglacial and paraperiglacial landsystems: concepts, temporal scales and spatial           distribution. Géomorphologie: rélief, processus, environnement, 14, 223-233.

Micheletti, N., Lambie,l C., Lane, S.N. (2015). Investigating decadal scale geomorphic dynamics in an Alpine mountain setting, Journal of Geophysical Research – Earth Surface, 120, 2155-2175.

Oppikofer, T., Jaboyedoff, M., Keusen, H. (2008). Collapse at the eastern Eiger flank in the Swiss Alps, Nat.   Geosci., 1, 531–535.

Perolo, P., Bakker, M., Gabbud, C., Moradi, G., Rennie, C., Lane, S.N. (2019). Subglacial sediment production and snout marginal ice uplift during the late ablation season of a temperate valley glacier, Earth Surf. Process. Landf., 44, 1117-1136.

Porter, P.R., Smart, M.J., Irvine-Fynn, R.D.L. (2019). Glacial sediment stores and their reworking Chapter       10 in Heckmann, T. and Morche, D. (Eds.), Geomorphology of proglacial systems: landform and sediment dynamics in recently deglaciated Alpine landscapes, Springer.

Ravanel, L., Deline, P. (2011). Climate influence on rockfalls in high-Alpine steep rockwalls: the north side of the Aiguilles de Chamonix (Mont Blanc massif) since the end of the ‘Little Ice Age’, The Holocene, 21, 357–365.

Riihimaki, C.A., MacGregor, K.R., Anderson, R.S., Anderson, S.P., Loso, M.G. (2005). Sediment evacuation and glacial erosion rates at a small alpine glacier, J. of Geophys. Research: Earth Surf., 110 F03003.

Staines, K.E.H., Carrivick, J.L., Tweed, F.S., Evans, A.J., Russell, A.J., Jóhannesson T., Roberts, M. (2015). A multi-dimensional analysis of pro-glacial landscape change at Sólheimajökull, southern Iceland, Earth Surf. Process. Landf., 40, 809-822.

Warburton, J. (1990). An alpine proglacial fluvial sediment budget, Geografiska Annaler, 21, 261- 272.