The best-developed glacial valley morphology appears to be restricted to landscapes with low rock uplift rates (less than or equal to 2 mm per year) and high relief, leading to long-turnover times. Where rock uplift rates exceed 2 mm per year, glacial valley morphology has generally been significantly modified in postglacial time. Interplay of glacial erosion and tectonic forcing governs the morphologic impact of glaciations on active orogens, by both influencing their height, and by altering the patterns of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape.