OPP-0118488 Pfeffer OPP-0118721
Basal sliding is the principle form of movement of most temperate glaciers and leads to glacier surging, causes glaciers to erode their beds, and often controls the overall glacier's mass distribution. A glacier's deformational velocity field can be modeled with some confidence, but there are no working models that will accurately predict the sliding motion of glaciers. In fact, the variables that would potentially go into a sliding model have not been fully established. Theoretically, sliding is promoted by both elevated water pressure and water storage at the bed. Previous field programs, however, have correlated sliding rate with either pressure or storage, with the majority of associations made with pressure. These observational programs have correlated sliding and subglacial conditions by using only limited spatially and temporally distributed measurements. This has made the task very difficult because the subglacial drainage system is transient and internal ice dynamics (e.g., longitudinal coupling) complicate the glacier's response to change at its lower boundary. The Principal Investigators will conduct a multifaceted study focusing on time/space variability in coupling between the subglacial hydrology and ice dynamics system which they believe is key to a new understanding of sliding dynamics. They will conduct a field campaign on the Bench Glacier, a temperate valley glacier in southeast Alaska. Various types of instrumentation will be used to collect a comprehensive data set of measurements of basal water pressure, surface motion, internal deformation, sliding velocity, video observations of the bed, and slug, pump, and tracer experiments on subglacial water flow. These data will include at least three elements which have not been previously addressed, thus enabling new explorations of the linkages between subglacial hydrology and glacier motion: 1) data will be collected at two length scales, including measurements spanning the entire glacier and detailed measurements focused on a small reach; 2) measurements will be made over a time period of at least a year, allowing short to long period cycles to be investigated; and 3) an automated survey instrument will allow for uninterrupted high-time resolution studies of glacier motion. During the first field season, they will focus on the long length scale (kilometers), with measurements of basal conditions and velocity made at locations spanning the length of the glacier. Data will be used to investigate the longitudinal coupling between the bed and ice dynamics. During the second field season, they will address a short length scale (10-100 meters), enabling local observations to be placed within the context of regional processes. This will permit measurements of surface uplift to be fully compared with both ice dynamics and hydrology to investigate the cause of the uplift. The resulting data set and analyses will be used to test and refine conceptual and numerical models for subglacial water flow and to establish links between hydrology and ice dynamics.
