Holocene alluvial fan and terrace formation in the Bowland Fells, Northwest England

Abstract

AbstractIn the Bowland Fells, Lancashire, northwest England, in the headwater valleys of the Hodder river system, is a suite of Holocene fluvial landforms. Debris cones and alluvial fans at tributary junctions, and river terraces along the main valleys post‐date late Pleistocene forms and pre‐date the modern valley floor alluvial forms. Eight 14C dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of Holocene erosion to be identified with debris cone/fan deposition taking place after c. 5400 BP but before c. 1900 BP and again at c. 900 BP. Some of the fans and cones are complex with deposits attributable to both phases; others are simple and attributable only to the later phase. In the headwaters an upper terrace at c. 5400 BP pre‐dates the cones and a lower terrace is contemporaneous with the first debris cone phase. Lower downvalley the youngest of three terraces date from c. 5000 BP or earlier indicating that the sequence is less complex downstream.