Supraglacial lake

A supraglacial lake is any pond of liquid water on the top of a glacier. Although these pools are wict|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 crevasse.

Effects on ice masses

Lakes of a diameter greater than ~300 m are capable of creating a fluid-filled crevasse to the glacier/bed interface.When these crevasses form, it can take a mere 2-18 hours to empty a lake, supplying warm water to the base of the glacier - lubricating the bed and causing the glacier to surge.cite conference
author = Krawczynski, M.J.
coauthors = Behn, M.D.; Das, S.B.; Joughin, I.
year = 2007
title = Constraints on melt-water flux through the West Greenland ice-sheet: modeling of hydro-fracture drainage of supraglacial lakes
url = http://www.agu.org/cgi-bin/wais?jj=C41B-0474
accessdate = 2008-03-04
booktitle=Eos Trans. AGU,
volume=88(52)
pages= Fall Meet. Suppl., Abstract C41B-0474] The rate of emptying such a lake is equivalent to the rate of flow of the Niagara Falls. Such crevasses, when forming on ice shelves, may penetrate to the underlying ocean and contribute to the breakup of the ice shelf.IPCC4/wg1/4]

Supraglacial lakes also have a warming effect on the glaciers; having a lower wict|albedo than ice, the water absorbs more of the sun's energy, causing warming and (potentially) further melting.

:"See ice sheet dynamics for more on the significance of supraglacial lakes on ice motion."

Context

Supraglacial lakes can occur in all glaciated areas.

The retreating glaciers of the Himalaya produce vast and long lived lakes, many kilometres in diameter and scores of metres deep. These may be bounded by moraines; some are deep enough to be density stratified.cite journal
author = Chikita, K.
coauthors = Jha, J.; Yamada, T.
year = 2001
title = Sedimentary effects on the expansion of a Himalayan supraglacial lake
journal = Global and Planetary Change
volume = 28
issue = 1-4
pages = 23–34
url = http://linkinghub.elsevier.com/retrieve/pii/S092181810000062X
accessdate = 2008-03-04
doi = 10.1016/S0921-8181(00)00062-X] Most have been growing since the 1950s; the glaciers have been retreating constantly since then.

A proliferation of supraglacial lakes preceded the collapse of the Antarctic Larsen B ice shelf in 2001,Fact|date=March 2008 and may have been connected.Fact|date=March 2008

Such lakes are also prominent in Greenland, where they have recently been understood to be large contributors to ice movement.

ediments

Sedimentary particles often accumulate in supraglacial lakes; they are washed in by the meltwater or rainwater that supplies the lakes. 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. The amount of debris atop the glacier also has a large effect. Naturally, long lived lakes have a different sedimentary record to shorter lived pools.

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.cite journal
author = Syverson, K.M.
year = 1998
title = Sediment record of short-lived ice-contact lakes, Burroughs Glacier, Alaska
journal = Boreas
volume = 27
issue = 1
pages = 44–54
url = http://www.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=4330149
accessdate = 2008-03-04]

Upon melting of the glacier, deposits may be preserved as superglacial till ("alias" supraglacial moraine).

Effect of global warming

It is currently unclear whether global warming is increasing the abundance of supraglacial lakes; upcoming research hopes to quantify the effect - if any - which the changing climate has. [http://www.whoi.edu/oceanus/viewArticle.do?id=9126 Details of supraglacial lake research] from Sarah Das, a specialist. Contains images.]

External links

* [http://bbs.keyhole.com/ubb/showthreaded.php?Number=1000926 Supraglacial lakes of West Greenland] in Google Earth.

References