Tidewater Glaciers

What is a Tidewater Glacier?

Tidewater glaciers are glaciers which extend out, and terminate into the sea [1]. They are part of a group of glaciers known as calving glaciers, as their main method of ice loss is through iceberg calving, instead of surface melt [1,2]. Calving icebergs currently accounts for up to 70% of the worlds annual mass transfer from glacial regions to the ocean [1].

tidewater-glacier
Whisky Glacier, a floating tidewater glacier in Whisky Bay, James Ross Island

Tidewater glaciers are found at latitudes of 45 and above, and are present in different glacial regions including Antarctica, Alaska, Greenland, Svalbard, and Patagonia [1,2].

Types of Tidewater Glacier

Mountain glaciers terminating into the ocean are called ‘tidewater glaciers’. ‘Tidewater outlet glaciers’ are glaciers which reach the ocean through fjords, branching off from ice caps, ice sheets or icefields [1].

Tidewater glaciers can either be grounded – where the glacier is in constant contact with the bed. Or they can be floating – when the terminus is floating on the sea water, or flowing into an ice shelf [1,3]. Grounded glaciers tend to be located in temperate regions such as Alaska, or Canada. And floating tidewater glaciers are commonly found in polar regions, namely Greenland, Svalbard, and Antarctica.

Tidewater Glaciers and Iceberg Calving

Calving icebergs are the most efficient method of losing mass from a glacier [4]. It is the dominant cause of mass loss from the Antarctic Ice Sheet [5], therefore, it is important to understand the process behind these calving events [1,4]

Iceberg calving occurs when there are faults in the glacier, known as crevasses. Crevasses can form when there stress and strain thresholds are reached on the glacier. The trigger for the iceberg calving events vary for both grounded and floating tidewater glaciers.

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A tidewater glacier with crevasses calving icebergs

Floating tidewater glacier

For a floating tidewater glacier, submarine melting of the underside of the glacier causes a direct loss of ice, as well as undercutting the floating glacier terminus or ice shelf [6]. This causes instability, resulting in complete collapse [1,6].

When the floating section of the tidewater is removed, the ice on the land is no longer supported from the buttressing ice shelf. It is then able to rapidly, and continuously calve icebergs. For example, the Larsen B ice shelf collapse in 2002 on the Antarctic Peninsula [4].

Grounded tidewater glaciers

Grounded tidewater glaciers calve when there is either a rapid thinning of the glacier surface, or a localised change in sea level. This change forces the glacier terminus to be out of equilibrium with the ocean, resulting in the terminus to be lifted and detached from the bed, causing the terminus to become buoyant [6]. During this process, the crevasses are able to isolate large blocks of ice which are then calved into icebergs.

Illustration of a grounded glacier during a calving event.

References


[1] Vieli, A., 2011. Tidewater glaciers, in: Singh, V.P., Singh, P., Haritashya, U.K. (Eds.), Encyclopedia of Snow, Ice and Glaciers. Springer, pp. 1175–1179.

[2] Benn, D.I., Hulton, N.R.J., Mottram, R.H., 2007. “Calving laws”, “sliding laws” and the stability of tidewater glaciers, in: Sharp, M. (Ed.), Annals of Glaciology, Vol 46, 2007, Annals of Glaciology. Int Glaciological Soc, Univ Ctr Svalbard UNIS, NO-9171 Longyearbyen, Norway. Benn, DI, Univ Ctr Svalbard UNIS, Box 156, NO-9171 Longyearbyen, Norway., pp. 123–130.

[3] van der Veen, C.J., 2002. Calving glaciers. Prog. Phys. Geogr. 26, 96–122. https://doi.org/10.1191/0309133302pp327ra

[4] Benn, D.I., and Evans, D.J.A., 2010. Glaciers and Glaciation. Hodder-Arnold, London

[5] Shepherd, A., Ivins, E., Rignot, E., Smith, B., Van Den Broeke, M., Velicogna, I., Whitehouse, P., Briggs, K., Joughin, I., Krinner, G., IMBIE Team, 2018. Mass balance of the Antarctic Ice Sheet from 1992 to 2017. Nature 558, 219–222. https://doi.org/10.1038/s41586-018-0179-y

[6] Benn, D.I., Astrom, J., Zwinger, T., Todd, J., Nick, F.M., Cook, S., Hulton, N.R., and Luckman, A. (2017) Melt under-cutting and buoyancy-driven calving from tidewater glaciers: new insights from discrete element and continuum model simulations. Journal of Glaciology. 63(240).

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