An analysis of landslides in Great Britain using soil texture, rainfall, and topography reveals contrasting failure conditions between organic and mineral soils

Rainfall-induced landslides cause millions of pounds in damage to infrastructure in Great Britain (GB) annually and occasionally result in human fatalities. Despite the risks, Great Britain has few policies or guidelines to mitigate landslides, and limited research has characterised their regional incidence. Peat landslides, found mainly in the British Isles and a handful sub-Antarctic islands, have recently gained attention for their destructive impacts and the loss of valuable terrestrial carbon. Given the environmental significance of peat, we examine the current knowledge gaps regarding the mechanical conditions that trigger peat failures and compare these with those governing failures in mineral soils. We start by empirically characterizing landslide incidence in GB considering landslide events recorded in the British Geological Survey (BGS) database. Soil texture, topographic, and antecedent rainfall data were acquired for the considered landslides. Organic landslides had significantly steeper slopes and higher antecedent rainfall sums than mineral landslides and occurred most frequently in late summer and early autumn months. Landslides in loam-textured soils were an order of magnitude more frequent than in other textures, and remained the most frequent after normalisation by soil-texture area, although other groups exhibited comparable area-normalised failure rates. Using a K-means clustering analysis, landslide groups exhibiting similar slope, soil, and rainfall characteristics were identified revealing unique inter-cluster spatial and temporal patterns. Organic landslides in the database could be roughly segregated as those that failed on shallow slopes with low antecedent rainfall in summer months ‘bog flows') and those that failed on steep slopes with varying antecedent rainfall which were interpreted to largely be mineral failures with a peat veneer (‘peaty-debris flows'). The failure mechanism of the former was likely seasonal drops in peat moisture content, which facilitated rainwater infiltration through desiccation cracks raising pore pressures within the peat mass, increasing peat landslide susceptibility in late summer months. These results can be used to guide more accurate landslide risk management considering region and preconditioning factors which is pertinent for recent peatland restoration activities in GB.