PROBLEMS OF STABILITY AND DRAINAGE OF ICE MASSES, AS SURFICIAL SEDIMENTS, AND APPLICATIONS TO THE LATE WEICHSELIAN GLACIAL EVENT IN THE NORTH OF IRELAND

All surficial sediments involve water in mechanisms of stabilization a nd self-regulation so as to maintain entropy and prolong morphological intactness. During a sediment 'Iifecycle', mass and energy is stored as the sediment builds up, and is expelled from the system by or as wa ter as the sediment degrades. Glacial systems often show an internal ( intrinsic) response to external (extrinsic) forcing mechanisms. Howeve r, this process-response varies throughout the ice mass 'lifecycle'. H igh magnitude events of mass and energy loss, such as jokulhlaups, cal ving events and surges, occur at the transition between extrinsic and intrinsic forcing mechanisms, and are important in increasing the inst ability of degenerating glacial systems by decreasing the amount of en ergy available in the system. These high magnitude events characterise present day subpolar ice masses. The distribution of late Weichselian -age drumlins and glaciofluvial sediments in the north of Ireland show s that ice mass reequilibriation processes responded to a variety of t rigger mechanisms-both intrinsic and extrinsic-and on different scales . High magnitude events were not characteristic of the northern Irish ice cover, and drumlinization and glaciofluvial sediment deposition we re largely successive with no intervening period of ice mass instabili ty. This contrasts with other marginal areas of the late Weichselian i ce sheets in which high magnitude events and glacial instability were dominant features.