A TARN is a glacier-formed lake, which is a body of water that has been created by the melting of a glacier. It is typically found in mountainous regions and is usually quite shallow. The shape of a TARN is often irregular due to the uneven terrain of the area in which it is located. Tarns are also known for their clear, blue-green waters, which are caused by the glacial silt that is suspended in the water.