Origin of the Lower Severn Valley River terraces by isostatic unloading of the lithosphere

River incision rate data, together with an isostatic unloading model, have been used to constrain the origin of the ‘staircase’ of Pleistocene river terraces in the Lower Severn Valley. Previous studies show that terrace cyclicity is mainly controlled by climate change, while their ‘staircase’ pattern is the consequence of crustal uplift: variously accounted for by isostatic unloading, ductile flow in the lower crust, and tectonics. Here, it is shown the crustal uplift can be explained by an isostatic unloading model that takes into account the generalized glaciation and deglaciation history of the British Isles, the topography of the Forest of Dean and Cotswold Hills, and the possibility of a lithosphere, rather than asthenosphere, stress relaxation. The model predicts that the flexural response to excavation (i.e. removal) of sediment by melt-water charged rivers, or ice retreat, following a deglaciation event would be fast initially and then slow. In the Anglian (∼450 ka), believed to be the most significant such event, the response is rapid enough to explain the oldest and highest of the Lower Severn Valley terraces (∼60 m) and gentle enough to explain, with a small ‘boost’ from younger events, the height of the youngest and lowest of the terraces (∼20 m).