Permanent lake of glaciers and ice sheets

Glacier lakes are formed as a consequence of melting of a glacier or icesheet, typically bordering to melting glaciers. In some cases these waterbodies can occur under the glacier. Glacier lakes are formed in depressions or crevices filled by melting water. In areas without depressions melting water runs as subglacial brook or river, and later discharges to alpine brooks or rivers (type C2.2a, and C.3.5d). Glacier lakes are often dammed by a rock threshold or a moraine ridge. If water volume increases, the lake can outburst through the damming.

Permanent or almost permanent ice formations are characteristics of glacier lakes, constituting of continuous ice sheets that may cover the entire surface for all the year or recede to part of the lake during summer, being accompanied or replaced by floating ice blocks. They may locally, seasonally or permanently, extend to the whole depth of the lake. Glacier lakes are mainly abiotic environments. Benthic and planktonic microalgae form ultraoligotrophic communities consisting of cold-adapted species; usually lakes are without any higher vegetation. If high mountain lakes or brooks are nearby, some aquatic mosses, macroalgae and macroinvertebrates may invade glacier lakes. In some cases also fish and waterfowl spreads to glacier lakes, particularly in water bodies on lower elevation or in coastal areas. A good example is the Jökulsárlón glacier lagoon in Iceland where fishes drift in from the sea along with the tides. Glacier lakes are also in contact with various other arctic and alpine habitats, usually unvegetated or with very sparse vegetation. Typical adjacent habitats are rocks, screes, boulder and gravel fields, moraine ridges or sandur-formations. Permanent glacier lakes occur in Europe only in a few countries, a majority of them in Iceland and Norway, Because of the small size of glaciers in the Alps the habitat is very rare there.

Water bodies can also be formed under the glacier. A special type of these water bodies occurs in Iceland where large glaciers (particularly Vatnajökull) lie above active volcanoes. Volcanic activity can melt large quantities of water under the ice, resulting in large-scale outburst of melting water with mud, gravel and stone. Several glacier lake outburst floods (GLOFs) are known from Iceland during the last centuries. An example is the outburst of the volcano Grimsvötn, situated under the Vatnajökull ice cap, in the 1990s. Also Myrdalsjökull is famous for these catastrophic events, called jökulhlaup in Icelandic.

Indicators of good quality:

• Long-term stable hydrology, reflected in a balance between accumulation of ice and melting of the glacier

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats