The Quaternary was a period of successive glaciations in the Vosges mountains. It was during the last phase, that of the Würm glaciation (around 80,000 to 10,000 years BC), that 3 lakes were born (Retournemer, Longemer, and Gerardmer). Gerardmer Lake is held back by a terminal moraine, which is a mass of glacial material. Lateral moraine's deposit collapses permanently block the natural valley of the Tholy downstream. The lake's emissary, the Jamagne, goes upstream of this valley.