Lichens, Soil Development and the Age of Holocene Valley Floor Landforms: Howgill Fells, Cumbria

Little is known of the post-glacial sequence of erosion and deposition in upland Britain. In the Carlingill valley, Howgill Fells, Cumbria, Late Pleistocene solifluction surfaces and a high fluvial terrace are dissected by the modern valley within which are Holocene low terraces, tributary alluvial cones and the modern valley floor. This paper establishes a lichen-based sequence for the development of the valley floor and a soil chronosequence on the post-glacial fluvial surfaces.Rhizocarpon geographicum-based lichenometry provides a framework for dating fluvial surfaces over the last 140 years and a multi-species lichen successional sequence can be identified over the same period. A chronosequence of podzol soil development can be identified on the basis of profile morphology, pH and organic content with clear age related differences between valley floor, low and high terraces, with the older high terrace and solifluction surfaces showing mature deep polzols. For the youngest soils sequential iron extraction has allowed the earliest stages of soil formation to be identified.The sequences accord with a regional pattern of early Holocene stabilisation and later disturbance. The modern valley floor shows contrasts between recently stabilised reaches where the channel has locked into bedrock and unstable reaches where the rate of channel migration accords with that of other unstable channels in upland Britain.