Supraglacial lake
A supraglacial lake is any pond of liquid water on the top of a glacier. Although these pools are ephemeral, they may reach kilometers in diameter and be several meters deep. They may last for months or even decades at a time, but can empty in the course of hours.
Lifetime
Lakes may be created by surface melting during summer months, or over the period of years by rainfall, such as monsoons. They may dissipate by overflowing their banks, or creating a
Effects on ice masses
Lakes of a diameter greater than ~300 m are capable of driving a fluid-filled crevasse to the glacier/bed interface, through the process of
Supraglacial lakes also have a warming effect on the glaciers; having a lower albedo than ice, the water absorbs more of the sun's energy, causing warming and (potentially) further melting.
Context
Supraglacial lakes can occur in all glaciated areas.
The retreating glaciers of the
A proliferation of supraglacial lakes preceded the collapse of the Antarctic
Such lakes are also prominent in Greenland, where they have recently been understood to contribute somewhat to ice movement.
Sediments
Sedimentary particles often accumulate in supraglacial lakes; they are washed in by the meltwater or rainwater that supplies the lakes.[4] The character of the sediment depends upon this water source, as well as the proximity of a sampled area to both the edge of the glacier and the edge of the lake.[4] The amount of debris atop the glacier also has a large effect.[4] Naturally, long lived lakes have a different sedimentary record to shorter lived pools.[4]
Sediments are dominated by coarser (coarse sand/gravel) fragments, and the accumulation rate can be immense: up to 1 metre per year near the shores of larger lakes.[4]
Upon melting of the glacier, deposits may be preserved as superglacial till (alias supraglacial moraine).
Effect of global warming
Greenland Ice Sheet
It was once unclear whether
Himalaya
Climate change is having a more severe effect on supraglacial lakes on mountain glaciers. In the Himalaya, many glaciers are covered by a thick layer of rocks, dirt, and other debris; this debris layer insulates the ice from the warmth of the sun, allowing more ice to stay solid when air temperatures rise above the melting point. Water collecting on the ice surface has the opposite effect, due to its high albedo as described in a previous section. Thus, more supraglacial lakes lead to a vicious cycle of more melting and more supraglacial lakes.[8] A good example is the Ngozumpa glacier, the longest glacier in the Himalayas, which counts numerous supraglacial lakes.
The drainage of supraglacial lakes on mountain glaciers can disrupt the internal plumbing structure of the glacier. Natural events such as landslides or the slow melting of a frozen moraine can incite drainage of a supraglacial lake, creating a glacial lake outburst flood. In such a flood, the lake water releases rushes down a valley. These events are sudden and catastrophic and thus provide little warning to people who live downstream, in the path of the water. In Himalayan regions, villages cluster around water sources, such as proglacial streams; these streams are the same pathways the glacial lake outburst floods travel down.
References
- ^ Krawczynski, M.J.; Behn, M.D.; Das, S.B.; Joughin, I. (2007). "Constraints on melt-water flux through the West Greenland ice-sheet: modeling of hydro-fracture drainage of supraglacial lakes". Eos Trans. AGU. Vol. 88. pp. Fall Meet. Suppl., Abstract C41B–0474. Archived from the original on 2012-12-28. Retrieved 2008-03-04.
- ^ Lemke, P.; Ren, J.; Alley, R.B.; Allison, I.; Carrasco, J.; Flato, G.; Fujii, Y.; Kaser, G.; Mote, P.; Thomas, R.H.; Zhang, T. (2007). "Observations: Changes in Snow, Ice and Frozen Ground" (PDF). In Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.B.; Tignor, M.; Miller, H.L. (eds.). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
- ^ .
- ^ S2CID 129000793. Retrieved 2008-03-04.
- ^ Details of supraglacial lake research from Sarah Das, a specialist. Contains images.
- ^ Howat, I M, S de la Peña, J H van Angelen, J T M Lenaerts, and M R van den Broeke. 2013. “Expansion of Meltwater Lakes on the Greenland Ice Sheet.” The Cryosphere 7 (1). doi:10.5194/tc-7-201-2013.
- ^ Poinar, K, I Joughin, S B Das, and M D Behn. 2015. “Limits to Future Expansion of Surface‐Melt‐Enhanced Ice Flow Into the Interior of Western Greenland.” Geophysical Research Letters. doi:10.1002/2015GL063192.
- ^ Benn, D I, T Bolch, K Hands, J Gulley, A Luckman, L I Nicholson, D Quincey, S Thompson, R Toumi, and S Wiseman. 2012. “Response of Debris-Covered Glaciers in the Mount Everest Region to Recent Warming, and Implications for Outburst Flood Hazards.” Earth-Science Reviews 114 (1-2). Elsevier B.V.: 156–74. doi:10.1016/j.earscirev.2012.03.008.