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A small surge of part of the margin of Breidamerkurjökull in Iceland was anticipated and successfully monitored by transducers and strain markers emplaced in sediments subsequently overridden by the glacier. The surge occurred as a consequence of a longitudinal compressional wave, which produced a 250m advance of the glacier margin at a rate of between 0.4 and 1.7m per day over a 6-month period. The glacier surface velocity and profile were regularly measured and water pressures in subglacial sediments recorded at 6-hour intervals by transducers that had been emplaced in the sediment at 11 separate locations prior to the surge.
These permitted the time dependent pattern of erosion and deposition during the surge to be reconstructed and related to the evolution of the hydraulic pressures, glacier velocity and ice loading. A relatively complete description of the time dependent mass flux of sediment is deduced, which permits key relationships relating to the processes of erosion and deposition to be inferred. Our model suggests that the activation of till deformation is strongly related to seasonal and diurnal variations of effective pressure driven by fluctuations in runoff from the glacier surface. The observations and theory permit us to constrain the rheological behaviour of the till.
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