Bench Glacier Project Home Participants Overview Borehole Drilling Borehole Video Hydrology Flow Dynamics Instrumentation Photos

Project Overview The primary mechanism by which temperate glaciers move is basal sliding.  The sliding rate is dependent upon the conditions at the bed of the glacier. Water at the bed is a particularly important factor controlling the sliding rate. The goal of this research is to investigate the linkages between sub-glacial hydrology and the movement of temperate valley glaciers. The research consists of both field measurements and computer modeling. Field research is being conducted on Bench Glacier, located in the Chugach Mountains, Alaska. Bench Glacier was chosen because it has a very simple geometry (i.e., no tributaries) and has only one minor ice fall.  The latter was required so that borehole drilling equipment could be hauled along the entire length of the glacier.  Bench Glacier with borehole sites in 2002. At least two holes were drilled at each site. Major goals of the field research are to install a network of sensors, spanning the entire length of the glacier, which will monitor the sub-glacial hydrological conditions. Measurements include water pressure, conductivity, turbidity and flow velocity. These data will be collected at 15 minute intervals for a period of at least two years. Detailed surveying of glacier velocity will accompany the hydrological measurements in order to interpreter the relationship between hydrology and flow dynamics. Detailed measurements will also be made in a smaller reach to investigate short length-scale processes. For more information see scientific summary. Location of Bench Glacier. Topographic map of Bench Glacier. Satellite image of Bench Glacier area. First Field Season Completed (see various topics for preliminary results) This phase of the project was completed during May and June of 2002.  A field party of 7 conducted field research, drilling and instrumenting borheoles and surveying.  Major accomplishments were: Ø The drilling equipment was hauled from the terminus to the headwall of the glacier installing 24 boreholes along the way.  Six boreholes were drilled in the accumulation area of the glacier --- we are aware of no other boreholes drilled in the accumulation area of a temperate glacier. Ø 18 of the boreholes were instrumented with "gophers" to measure water pressure, conductivity, turbidity, and flow velocity for a period of one year. These holes are distributed in nine sites, with two holes per site. Ø Each of the holes were logger with a borehole video camera. Ø Repeated slug tests were performed in a network of boreholes. Ø High time and space resolution velocity measurements were made using an automatic total station theodolite. Ø Subglacial and englacial imaging was done with a high resolution ground penetrating radar system. In September 2002 a crew of three returned to the glacier to download data from the data loggers and place radio transmitters on the data loggers so that they can be located next Spring after burial by 4-6 meters of winter snow.  Each of the nine data loggers was functioning properly.  A (suspected) wolverine had chewed the wires from two gophers, between the top of the boreholes and the data loggers. These were repaired, although some data from the summer were lost. SCIENCE SUMMARY Basal sliding is the principle form of movement of most temperate glaciers. Sliding is the mechanism that leads to glacier surging, causes glaciers to erode their beds, and in many cases controls the overall mass distribution of a glacier. Basal sliding is, therefore, of fundamental importance to numerous topics within glaciology. Yet, while we are able to model a glacier's deformational velocity field with some confidence, we have 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 even been fully established. A large body of work has addressed the link between subglacial hydrology and sliding from both theoretical and observational perspectives. Theory suggests that sliding is promoted by both elevated water pressure and water storage at the bed. Past field programs, however, have correlated sliding rate with either pressure or storage, with the majority of associations made with pressure. These observational programs have been faced with correlating sliding and subglacial conditions using only limited spatially and temporally distributed measurements. This has made the task particularly difficult as 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. We believe that the key to a new understanding of sliding dynamics is a multifaceted study focusing on time/space variability in coupling between the subglacial hydrology and ice dynamics systems. Our research will take this approach through a field campaign on a temperate valley glacier (Bench Glacier, Alaska). Modern technology will be used to collect a uniquely comprehensive data set consisting 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 addressed by previous studies, 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; 3) an automated survey instrument will allow for uninterrupted high-time resolution studies of glacier motion. One field season 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. A second field season 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 in order to investigate the cause of the uplift. The resulting data set and analysis will be used to test and refine conceptual and numerical models for subglacial water flow and to establish links between hydrology and ice dynamics.