Composite Mudflows on the Antrim Coast of North-East Ireland

Abstract

A series of composite mudflows have affected adversely the road communications along segments of the coast of north-east County Antrim, Northern Ireland. Field mapping and air photograph interpretation have established the distribution of these phenomena. Detailed investigations of the movement and of the morphology of the mudflows have been made at a number of sites, principally at Minnis North.The movement of the mudflows is initiated by the seasonal accumulation of rainfall leading to saturation of the inherently unstable Liassic shales which underlie several hundreds of feet of chalk and basalt strata forming the Antrim Plateau. Large scale, late-Pleistocene slumping on the relatively steep coastal slope along the eastern edge of the plateau has exposed the Liassic shales with high angles of dip. This permits comparatively rapid absorption of water and consequent deterioration of the cohesion of the shales. This has led to extensive development of bowl-slides, flow tracks defined by marked shear planes and depositional toe-zones, all of which are active at present.