Meltwater

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. After that, leftover water will flow into oceans causing sea levels to rise. 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. Agriculture in Wyoming and Alberta relies on water sources made more stable during the growing season by glacial meltwater. Cities that rely heavily on glacial meltwater include La Paz and El Alto in Bolivia, about 30%. ==Glacial meltwater==

, in Antarctica 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 because of the Tyndall Effect, giving a milky turquoise or bluish appearance, the exact shade determined by particle size. Meltwater also acts as a lubricant in the basal sliding of glaciers. GPS measurements of ice flow have revealed that glacial movement is greatest in summer when the meltwater levels are highest. Glacial meltwater can also affect important fisheries, such as in Kenai River, Alaska. ==Rapid changes==

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. Global warming 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. Historically Meltwater pulse 1A was a prominent feature of the last deglaciation and took place 14.7-14.2 thousand years ago. The snow of glaciers in the central Andes melted rapidly due to a heatwave, increasing the proportion of darker-coloured mountains. With alpine glacier volume in decline, much of the environment is affected. These black particles are recognized for their propensity to change the albedo – or reflectance – of a glacier. Pollution particles affect albedo by preventing sun energy from bouncing off a glacier's white, gleaming surface and instead absorbing the heat, causing the glacier to melt. ==See also==