Paper No. 7
Presentation Time: 10:30 AM
INTEGRATING TERRESTRIAL LASER SCANNING, GROUND-PENETRATING RADAR, AND TIME-LAPSE PHOTOGRAPHY TO UNDERSTAND SURFICIAL PROCESSES/MORPHOLOGY AND SUBSURFACE ARCHITECTURE OF ICY DEBRIS FANS IN DEGLACIATING ALPINE ENVIRONMENTS
Deglaciation in alpine environments is characterized by mass wasting processes that form talus cones, rock glaciers, and alluvial fans. Icy debris fans are a less explored landform dominated by ice avalanching and debris flow. Fans occur below ice caps or hanging glaciers and along margins of valley glaciers. Reconnaissance studies in Alaska and New Zealand emphasized direct observations and studies of depositional processes, but lack an understanding of the subsurface geometry and evolution of these features. Repeated geophysical surveys, time-lapse photography, and direct observations are beginning to characterize the 3-D geometry of icy debris fans. Terrestrial laser scanning (TLS) quantifies the surface area and morphology of the landforms and deposits. Ground-penetrating radar (GPR) provides subsurface data, including fan thickness, depth to underlying bedrock/glacier/talus, and internal fan architecture. Time-lapse photography documents the types and frequency of depositional events, while TLS is being used to estimate the volumes of individual events. Integrated, these techniques will provide a basis for estimating the annual contributions of ice and clastic debris via the fans to valley glaciers. Repeat field observations show changes in fan morphologies, but repeat TLS, GPR, and time-lapse photography over the next three years will better quantify these changes. Documenting such changes is important for evaluating the amount of ice being transferred from icy debris fans to valley glaciers. A preliminary result of this integrated approach is that variations in fan subsurface geometries correspond with surface observations. Fans with similar area may exhibit substantial variation in thickness due to differences in supply. For example, fans with greater ice supply are more convex and have greater thickness, whereas fans with less ice supply are less convex and dominated by debris flow. GPR is also helping to explain surface features. For example, surface depressions and moulins observed down-glacier of an anomalously large fan correspond with GPR soundings showing slower velocities that indicate significant subsurface water content compared with other locations. This is consistent with water moving from icy fans to the lower portion of the valley glacier.