Morphology and causes of recent peat slides on Skerry Hill,Co. Antrim,Northern Ireland

Two shallow translational slides occurred in blanket peat on Skerry Hill, Co. Antrim, in November 1991 at sites adjacent to slides activated c. 25 years ago. Heavy rainfall, degraded drainage ditches and slope morphology are considered to have been important factors contributing to peat instability. The failure planes are located close to the peat base, at the boundary between less compact fibrous peat above and more compact humified peat below. The preservation of large blocks and rafts of intact peat and the limited amount of liquefied peat in the debris tongues is thought to reflect the degree of peat humification. There is also some evidence to suggest that the peat was probably undersaturated at the time of failure and this may have assisted preservation of intact peat blocks. Tension cracks, resulting from either short-term desiccation or long-term slow mass movement, are thought to have facilitated the rapid transfer of heavy rain to the subsurface peat, causing high pore-water pressures and lubrication of the failure planes. Vegetation recolonization will probably follow a pattern similar to that observed on the adjacent earlier slides.