Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be produced during volcanic eruptions, in a similar way in which the more dangerous lahars form.
When meltwater pools on the surface rather than flowing, it forms melt ponds. As the weather gets colder meltwater will often re-freeze. Meltwater can collect or melt under the ice's surface. These pools of water, known as subglacial lakes can form due to geothermal heat and friction.
This section needs expansion. You can help by adding to it. (May 2008)
Meltwater provides drinking water for a large proportion of the world's population, as well as providing water for irrigation and hydroelectric plants. This meltwater can originate from seasonal snowfall, or from the melting of more permanent glaciers. Climate change threatens the precipitation of snow and the shrinking volume of glaciers.
Some cities around the world have large lakes that collect snow melt to supplement water supply. Others have artificial reservoirs that collect water from rivers, which receive large influxes of meltwater from their higher elevation tributaries. Snow melt hundreds of miles away can contribute to river replenishment. Snowfall can also replenish groundwater in a highly variable process. Cities that indirectly source water from meltwater include Melbourne, Canberra, Los Angeles, Las Vegas among others.
In North America, 78% of meltwater fllows west of the Continental Divide, and 22% flows east of the Continental Divide. Agriculture in Wyoming and Alberta relies on water sources made more stable during the growing season by glacial meltwater.
The Tien Shan region in China once had such significant glacial runoff that it was known as the "Green Labyrinth", but it has faced significant reduction in glacier volume from 1964 to 2004 and become more arid, already impacting the sustainability of water sources.
In tropical regions, there is much seasonal variability in the flow of mountainous rivers, and glacial meltwater provides a buffer for this variability providing more water security year-round, but this is threatened by climate change and aridification. Cities that rely heavily on glacial meltwater include La Paz and El Alto in Bolivia, about 30%. Changes in the glacial meltwater are a concern in more remote highland regions of the Andes, where the proportion of water from glacial melt is much greater than in lower elevations. In parts of the Bolivian Andes, surface water contributions from glaciers are as high as 31-65% in the wet season and 39-71% in the dry season.
Glacial meltwater comes from glacial melt due to external forces or by pressure and geothermal heat. Often, there will be rivers flowing through glaciers into lakes. These brilliantly blue lakes get their color from "rock flour", sediment that has been transported through the rivers to the lakes. This sediment comes from rocks grinding together underneath the glacier. The fine powder is then suspended in the water and absorbs and scatters varying colors of sunlight, giving a milky turquoise appearance.
Meltwater can be an indication of abrupt climate change. An instance of a large meltwater body is the case of the region of a tributary of Bindschadler Ice Stream, West Antarctica where rapid vertical motion of the ice sheet surface has suggested shifting of a subglacial water body.
It can also destabilize glacial lakes leading to sudden floods, and destabilize snowpack causing avalanches. Dammed glacial meltwater from a moraine-dammed lake that is released suddenly can result in the floods, such as those that created the granite chasms in Purgatory Chasm State Reservation.
In a report published in June 2007, the United Nations Environment Programme estimated that global warming could lead to 40% of the world population being affected by the loss of glaciers, snow and the associated meltwater in Asia. The predicted trend of glacial melt signifies seasonal climate extremes in these regions of Asia. Historically Meltwater pulse 1A was a prominent feature of the last deglaciation and took place 14.7-14.2 thousand years ago.
In the media
- Qin, Yue; Abatzoglou, John T.; Siebert, Stefan; Huning, Laurie S.; AghaKouchak, Amir; Mankin, Justin S.; Hong, Chaopeng; Tong, Dan; Davis, Steven J.; Mueller, Nathaniel D. (May 2020). "Agricultural risks from changing snowmelt". Nature Climate Change. 10 (5): 459–465. Bibcode:2020NatCC..10..459Q. doi:10.1038/s41558-020-0746-8. ISSN 1758-6798. S2CID 216031932.
- Milner, Alexander M.; Khamis, Kieran; Battin, Tom J.; Brittain, John E.; Barrand, Nicholas E.; Füreder, Leopold; Cauvy-Fraunié, Sophie; Gíslason, Gísli Már; Jacobsen, Dean; Hannah, David M.; Hodson, Andrew J. (2017-09-12). "Glacier shrinkage driving global changes in downstream systems". Proceedings of the National Academy of Sciences. 114 (37): 9770–9778. Bibcode:2017PNAS..114.9770M. doi:10.1073/pnas.1619807114. ISSN 0027-8424. PMC 5603989. PMID 28874558.
- "Snowfall giving Lake Mead a lift". Las Vegas Review-Journal. 2011-08-07. Retrieved 2021-05-30.
- "Melting snow and groundwater levels in Sierra Nevadas". ScienceDaily. Retrieved 2021-05-30.
- Castellazzi, P.; Burgess, D.; Rivera, A.; Huang, J.; Longuevergne, L.; Demuth, M. N. (2019). "Glacial Melt and Potential Impacts on Water Resources in the Canadian Rocky Mountains". Water Resources Research. 55 (12): 10191–10217. Bibcode:2019WRR....5510191C. doi:10.1029/2018WR024295. ISSN 1944-7973.
- "Glacier melt and water security". Imperial College London. Retrieved 2021-05-30.
- Guido, Zack; McIntosh, Jennifer C.; Papuga, Shirley A.; Meixner, Thomas (2016-12-01). "Seasonal glacial meltwater contributions to surface water in the Bolivian Andes: A case study using environmental tracers". Journal of Hydrology: Regional Studies. 8: 260–273. doi:10.1016/j.ejrh.2016.10.002. hdl:10150/626096. ISSN 2214-5818.
- Aas, Eyvind; Bogen, Jim (1988-04-01). "Colors of glacier water". Water Resources Research. 24 (4): 561–565. Bibcode:1988WRR....24..561A. doi:10.1029/WR024i004p00561. ISSN 1944-7973.
- Garner, Rob (2013-07-22). "'Like Butter': Study Explains Surprising Acceleration of Greenland's Inland Ice". NASA. Retrieved 2016-05-12.
- Peters, Leo E.; Anandakrishnan, Sridhar; Alley, Richard B.; Smith, Andrew M. (2007-03-01). "Extensive storage of basal meltwater in the onset region of a major West Antarctic ice stream". Geology. 35 (3): 251–254. Bibcode:2007Geo....35..251P. doi:10.1130/G23222A.1. ISSN 0091-7613.
- "Melting Ice—A Hot Topic? New UNEP Report Shows Just How Hot It's Getting". United Nations Environment Programme (UNEP). 2007-06-04. Retrieved 2016-05-12.
- Goudie, Andrew (September 2006). "Global warming and fluvial geomorphology". Geomorphology. 79 (3–4): 384–394. Bibcode:2006Geomo..79..384G. doi:10.1016/j.geomorph.2006.06.023.
- Webster, Jody M.; Clague, David A.; Riker-Coleman, Kristin; Gallup, Christina; Braga, Juan C.; Potts, Donald; Moore, James G.; Winterer, Edward L.; Paull, Charles K. (2004). "Drowning of the −150 m reef off Hawaii: A casualty of global meltwater pulse 1A?". Geology. 32 (3): 249. Bibcode:2004Geo....32..249W. doi:10.1130/g20170.1.