Microscale evidence of the role of water during the emplacement of mass flows in glacial environments

Microscale analysis of unlithified glacial soils can provide far greater detail regarding their depositional and deformation histories than can be obtained from macroscale studies alone. This paper presents the results of three detailed case studies that examine the processes occurring during overriding and emplacement of mass flows in glacial environments: (i) laminated soils deposited in a proglacial lake setting at Heinabergsjokull, Iceland; (ii) a channelized, ice-marginal to submarginal mass flow at Whitburn (County Durham), England; and (iii) a mass flow exposed at Carstairs, central Scotland that was emplaced in a glaciofluvial to glaciolacustrine setting. Microscale evidence from all three sites is combined to develop a conceptual model of the role played by water during mass flow; from the initial soil disruption under and/or in front of an advancing mass flow, to the formation of a basal shear zone facilitating mass-flow transport and emplacement, through to the decoupling of the flow from the underlying substrate as a result of the injection of fluidized soil along its base. The development of these detachments during mass flow has the potential to increase the velocity of the flow and its runout distance, increasing the potential impact of these geohazards.