DETECTION OF WATER PATHWAYS IN THE ACTIVE LAYER: RESULTS OF GROUND PENETRATING RADAR GPR AND CONDUCTIVITY SURVEYS AT GILPIN PEAK ROCK GLACIER, YANKEE BOY BASIN, CO, USA

Rock glaciers represent significant debris transport systems and primary stores for permafrost in periglacial regions. The mixtures of rock debris and permafrost that comprise rock glaciers are typically insulated by a 1-2 m thick mantle of blocky rock debris in which seasonal snow and ice is stored. This zone is referred to as the ‘active layer' because the amount of water and ice contained within fluctuates with variations in snowfall accumulation rates, seasonal climatic conditions, and talus accumulation rates. This characteristic of rock glaciers makes them especially sensitive to climatic changes that affect alpine environments, and thus, they may serve as principal climatological indicators, particularly at latitudes and elevations below those of glaciers.

The amount of snow and ice that can be incorporated in the active layer is subject to fluctuations in the yearly precipitation over the mountain range in which a rock glacier is located. Some factors that affect orographic snow cover are temperature, aspect, cloud cover, and wind. Moderate Resolution Imaging Spectroradiometer (MODIS) images obtained by NASA also indicate that large amounts of wind-blown dust can shorten the melting time for accumulations of snow in mountain ranges.

In an effort to develop a better understanding of the hydrologic characteristics of the active layer and its response to climatic changes, GPR and electromagnetic induction surveys were conducted in a centrally located furrow of the Gilpin Peak Rock Glacier. Within the furrow, meltwater from snow pack was observed infiltrating the active layer and reappearing 15 meters down slope at the terminus of the furrow. GPR profiles generated using 100 MHz centerpoint frequency indicates that the water pathway, which changes course within the active layer, does not conform strictly to the furrow. Induction conductivity measurements also suggest that the flowing water penetrates to the bottom of the active layer and then reemerges at the furrow terminus.