Although all glaciers flow, the way in which they flow is highly variable. We already know that the thermal regime can impact on glacier flow, with cold-based glaciers being frozen to their bed and flowing very slowly, and with warm-based glaciers having lots of water at their bed, which can reduce friction, enhance ice deformation and result in faster flowing glaciers. We also know that glaciers range from temperate valley glaciers to ice streams. However, some glaciers do not flow at a constant speed; instead, they are subjected to cyclical flow instabilities. These glaciers have been called ‘surging glaciers’ or ‘surge-type’ glaciers, and they typically have long periods of quiescence, with thinning, melting, downwasting and little forward movement, and short semi-periodical periods of rapid velocity, where they can advance dramatically. On Svalbard, in the high Arctic, the quiescent periods can last ~100 years and the fast-flow phase 1-5 years, although it varies regionally and by glacier[2-4].
The lower reaches of stagnant quiescent-phase glaciers often downwaste and thin in situ, which can result in thick accumulations of debris on their snouts. During this time, surge-type glaciers build up a reservoir of ice in their upper reaches during their quiescent phases. This reservoir is then depleted during the surge phase. Surges apparently arise from a combination of the deformable properties of the subglacial sediment, combined with changes in glacier thermal regime and feedbacks that disturb subglacial hydrology[5-7]. The surge starts when a critical threshold is passed, resulting in a critical basal shear stress (see Glacier Flow). This threshold is determined by a number of external factors, including the accumulation rate and glacier thickness and steepness. When the gravitational driving force of the glacier exceeds the friction at the base, changes occur in the subglacial system. Friction is decreased, subglacial deformation is enabled, and a surge occurs. The surge ends once either the reservoir is depleted, or a change occurs in the hydrological system.
The occurrence of surging is relatively unpredictable, and our understanding of surging glaciers is limited. This is a significant impediment to our understanding of melting of high Arctic glaciers, and makes it difficult to predict future sea level rise.
Surging glacier features
Surging glaciers typically produce a characteristic range of landforms[7-14]. Landforms characteristic of surges include:
- Concertina eskers or zig-zag eskers
- Thrust moraine complexes
- Crevasse-squeeze ridges
- Multiple stacked diamictons
- Tectonised sediments
- Hummocky moraine
Actively surging glaciers often have a shear line between fast- and slow-moving ice, and there may be ‘strandlines’ on the valley sides, where the glacier has rapidly thinned. There may be numerous crevasses, folding[16, 17], deformed longitudinal flow stripes (see post here), looped medial moraines[15, 18] and fragmented, digitate tidewater glacier termini.
Quiescent-phase glaciers, on the otherhand, are characterised by a pitted surface with lots of lakes, a dark surface with abundant debris, relict looped moraines and a slow velocity.
Other kinds of flow instability
In general, surge-type glaciers have not been recognised in Antarctica. However, there are many reasons why a glacier may experience flow instabilities. For example, around the Antarctic Peninsula, glaciers were observed to accelerate following the abrupt removal of an ice shelf.
1. Hagen, J.O., Liestøl, O., Roland, E., and Jørgensen, T., Glacier atlas of Svalbard and Jan Mayen. 1993, Norsk Polarinst. Medd.: Oslo.
2. Jiskoot, H., 2011. Dynamics of Glaciers, in Encyclopedia of snow, ice and glaciers, V.P. Singh, P. Singh, and U.K. Haritashya, Editors. Springer: Dordrecht, The Netherlands. p. 245-256.
3. Jiskoot, H., Murray, T., and Boyle, P., 2000. Controls on the distribution of surge-type glaciers in Svalbard. Journal of Glaciology, 2000. 46(154): p. 412-422.
4. Murray, T., Strozzi, T., Luckman, A., Jiskoot, H., and Christakos, P., 2003. Is there a single surge mechanism? Contrasts in dynamics between glacier surges in Svalbard and other regions. J. Geophys. Res., 2003. 108(B5): p. 2237.
5. Cuffey, K.M. and Paterson, W.S.B., 2010. The Physics of Glaciers, 4th edition. 2010: Academic Press. 704.
6. Rippin, D., Willis, I., Arnold, N., Hodson, A., Moore, J., Kohler, J., and Björnsson, H., 2003. Changes in geometry and subglacial drainage of Midre Lovénbreen, Svalbard, determined from digital elevation models. Earth Surface Processes and Landforms, 2003. 28(3): p. 273-298.
7. Mansell, D., Luckman, A., and Murray, T., 2012. Dynamics of tidewater surge-type glaciers in northwest Svalbard. Journal of Glaciology, 2012. 58(207): p. 110-118.
8. Grant, K.L., Stokes, C.R., and Evans, I.S., 2009. Identification and characteristics of surge-type glaciers on Novaya Zemlya, Russian Arctic. Journal of Glaciology, 2009. 55(194): p. 960-972.
9. Bennett, M.R., Hambrey, M.J., Huddart, D., Glasser, N.F., and Crawford, K., 1999. The landform and sediment assemblage produced by a tidewater glacier surge in Kongsfjorden, Svalbard. Quaternary Science Reviews, 1999. 18(10â€“11): p. 1213-1246.
10. Glasser, N.F. and Hambrey, M.J., 2001. Styles of sedimentation beneath Svalbard valley glaciers under changing dynamic and thermal regimes. Journal of the Geological Society, London, 2001. 158: p. 697-707.
11. Glasser, N.F., Hambrey, M.J., Crawford, K.R., Bennett, M.R., and Huddart, D., 1998. The structural glaciology of Kongsvegen, Svalbard, and its role in landform genesis. Journal of Glaciology, 1998. 44(146): p. 136-148.
12. Hambrey, M.J., Bennett, M.R., Glasser, N.F., and Huddart, D., 2001. High-Arctic glaciers as analogues for glacial landform development in Britain. Geology Today, 2001. 17(1): p. 24-28.
13. Huddart, D. and Hambrey, M.J., 1996. Sedimentary and tectonic development of a high-arctic, thrust-moraine complex: Comfortlessbreen, Svalbard. Boreas, 1996. 25(4): p. 227-243.
14. Evans, D.J.A. and Rea, B.R., 1999. Geomorphology and sedimentology of surging glaciers: a land-systems approach. Annals of Glaciology, 1999. 28: p. 75-82.
15. Hambrey, M.J. and Dowdeswell, J.A., 1994. Flow regime of the Lambert Glacier-Amery Ice Shelf system, Antarctica: structural evidence from Landsat imagery. Journal of Glaciology, 1994. 20(401-406): p. 401-406.
16. Goodsell, B., Hambrey, M.J., Glasser, N.F., Nienow, P., and Mair, D., 2005. The structural glaciology of a temperate valley glacier: Haut Glacier d’Arolla, Valais, Switzerland. Arctic, Antarctic and Alpine Research, 2005. 37(2): p. 218-232.
17. Hambrey, M.J. and Lawson, W., 2000. Structural styles and deformation fields in glaciers: a review, in Deformation of Glacial Materials, A.J. Maltman, B. Hubbard, and M.J. Hambrey, Editors. Geological Society of London, Special Publication: London. p. 59-83.
18. Copland, L., Sharp, M.J., and Dowdeswell, J.A., 2003. The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic. Annals of Glaciology, 2003. 36(1): p. 73-81.
19. De Angelis, H. and Skvarca, P., 2003. Glacier surge after ice shelf collapse. Science, 2003. 299: p. 1560-1562.