Pictured is Summit Lake, a tarn on the north face of Mount Evans and east face of Mount Spalding in Colorado. It sits at an altitude of 12,836 feet. Image source
Etymology: From the Old Norse word tjörn literally translating into "pond."
The word is also used in the region of Northern England to describe any pond thereabouts.
Variations of the word are used in Scandinavian languages to describe ponds or small lakes in forests that are closely hugged by vegetation.