An alpine lake is a high-altitude lake in a mountainous area, usually near or above the tree line, with extended periods of ice cover. These lakes are commonly glacial lakes formed from glacial activity (either current or in the past) but can also be formed from geological processes such as volcanic activity (volcanogenic lakes) or landslides (barrier lakes). Many alpine lakes that are fed from glacial meltwater have the characteristic bright turquoise green color as a result of glacial flour, suspended minerals derived from a glacier scouring the bedrock. When active glaciers are not supplying water to the lake, such as a majority of Rocky Mountains alpine lakes in the United States, the lakes may still be bright blue due to the lack of algal growth resulting from cold temperatures, lack of nutrient run-off from surrounding land, and lack of sediment input. The coloration and mountain locations of alpine lakes attract lots of recreational activity.
Alpine lakes are some of the most abundant types of lakes on Earth. In the Swiss Alps alone, there are nearly 1,000 alpine lakes, most of which formed after the Little Ice Age. As global temperatures continue to rise, more alpine lakes will be formed as glaciers recede and provide more run-off to surrounding areas, and existing lakes will see more biogeochemical changes and ecosystem shifts. An alpine lake's trophic state (i.e., level of biological productivity) progresses with age (e.g., low productivity after formation and increased productivity with vegetation and soil maturity in the surrounding watershed), but anthropogenic effects such as agriculture and climate change are rapidly affecting productivity levels in some lakes. These lakes are sensitive ecosystems and are particularly vulnerable to climate change due to the highly pronounced changes to ice and snow cover. Due to the importance of alpine lakes as sources of freshwater for agricultural and human use, the physical, chemical, and biological responses to climate change are being extensively studied.
