Tarns, also known as corrie lochs, are pools or lakes formed in glacial mountains and high country lakes. The word is derived from an Old Norse word tjorn, which means pond.
They are formed near glacial features such as kettleholes and cirque basins, and erosional landforms such as small fault scarps and slumps. When excavating for pipelines through regions with ecological features such as tarns, it is beneficial to use trenchless construction methods such as directional drilling and microtunneling so that the ecological balance of such wetlands are not disturbed.
Trenchlesspedia Explains Tarn
A cirque means a circle but is similar in form to an amphitheater. It is formed when soil erodes from beneath a glaciers bergschrund or a crevasse near the exposed rock. When rainwater or a river fills up the cirque, a tarn is created. A tarn associated with moving glaciers will scatter light from sediment ground by glaciers, making the water look colorful, indicating the presence of actively moving ice.
At the margins, it is not uncommon to see low turfs extending from the water level to surrounding vegetation such as forest or grassland. Aquatic and terrestrial species can be found in tarns but decrease with increasing altitude.