A thermally complex glacier with both warm and cold ice. Warm ice usually occurs where the ice is thickest, as a result of geothermal heating, while the snout and margins of the glacier are frozen to the bed. See Roberson et al. (2011) Geograf. Series A 93, 71 DOI: 10.1111/j.1468–0459.2011.00420 on the physical properties of a polythermal valley glacier in Norway.