Summary

Measurements of surface movements and pore-water pressures in a mudslide at Minnis North, north-eastern Ireland, are presented. This feature comprises steep feeder mudslides leading down to a more gently inclined accumulation mudslide, from which a steep front slope descends to the coast road. Frequent surges of the mudslide, which discharges considerable quantities of debris on to this road, are described and discussed. In one of these, pore-water pressures and surface movements were monitored up to failure and the surge itself witnessed by one of the authors. It is concluded that the surges generally originate through‘undrained loading’ of the rear of the accumulation slide by the feeder slides. Attention is drawn particularly to the danger inherent in situations where large volumes of underconsolidated and therefore potentially highly mobile material can collect above a steep front slope and to the difficulty, in the case studied, of obtaining warning of failure. Evidence is also presented to show that this danger is increased if surface streams are present on the mudslide.

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