A hanging valley is a tributary valley that is elevated above the main valley floor, often formed by glacial activity. As glaciers carve deep U-shaped valleys, smaller tributary glaciers create shallower valleys, which later become “hanging” when the glaciers retreat. Hanging valleys are important in studying glacial geomorphology and the evolution of mountain landscapes.
Reference: Benn, D. I., & Evans, D. J. A. (2010). Glaciers and Glaciation. Routledge.