Formational Conditions of Ribbed Moraine in Norway: A Distribution Analysis and Ribbed Moraine Inventory

Abstract. Ribbed moraines are common landforms in regions formerly glaciated by the Fennoscandian, British and Laurentide ice sheets. Their process of formation is disputed, as formation conditions are hard to reconstruct. With this work, we address this issue through a combination of a comprehensive ribbed moraine inventory of mainland Norway, mapped topographic information, and modelled glacial and hydrological information. First, a detailed 10 metre resolution ribbed moraine dataset is produced for the entire mainland Norway, which is used in combination with spatial statistics to isolate common distributions for ribbed moraines in nine series of data. These values include (a) topographic (elevation, slope and curvature), (b) glacial (basal temperature, ice thickness and ice velocity), and (c) hydrological values (flow accumulation, hydraulic head and hydraulic gradient). We derive mean conditions at 21000 years before present and compare values for areas of ribbed moraines and an equal area of land where ribbed moraines are not present. Our findings show that (a) ribbed moraines typically form in flat, low gradient and low curvature depressions with a low hydraulic gradient, (b) hydraulic head, hydraulic gradient and ice velocity are globally important for ribbed moraine formation, while factors such as elevation and ice thickness are too spatially variable for a wide-scale link to be drawn, but they show a strong local relationship, (c) ribbed moraines are present in areas where ice flow was relatively slow, (d) occurrence of ribbed moraines in areas of high hydraulic head, low hydraulic gradient and low ice velocity suggests that ribbed moraines formed in transitional areas between slow and fast ice flow, which may resemble a “patchwork” of slippery and sticky spots of high and low frictional resistance. However, these relationships are not definite, as we simply note relationships rather than process observations, and as such we conclude the possibility of an “equifinality” theory explanation for the formation of ribbed moraines.