ICE DEFORMATION AT THE CONFLUENCE OF 2 GLACIERS INVESTIGATED WITH CONCEPTUAL MAP-PLANE AND FLOWLINE MODELS

Using analytical and numerical techniques, a two-dimensional (2-D) map -plane model and a 2-D flowline model are utilized to elucidate the ho rizontal and vertical ice deformation at the confluence of two glacier s. For a perfectly symmetrical confluence, the junction point of the t wo tributaries can be modeled as a no-slip/free-slip transition. A str ongly localized surface depression develops around the junction point, accompanied by two broadly elevated zones positioned close to the mar gins of the tributaries facing the junction point. The confluence cent er line is subjected to horizontal longitudinal extension and a transv erse compression. The compression generally exceeds the concomitant lo ngitudinal extension in magnitude. Depth-integrated vertical strain ra tes along the center line are positive (extension), but the strain-rat e variation with depth depends critically on the type of basal boundar y conditions at the glacier bed. For a no-slip boundary condition, ver tical strain rates change from positive at the surface to negative clo se to the base, whereas for a free-slip boundary condition (perfect sl iding) vertical strain rates are positive throughout the depth. These theoretical results are compared with field measurements from Unteraar gletscher, Bernese Alps, Switzerland.