Terminus Dynamics and Active Deformation of Proglacial Sediments at an Advancing Glacier: Taku Glacier, Alaska

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Motyka00221307Taku Glacier has been steadily advancing for the last several decades, excavating its bed and entrenching itself into glaciomarine, fluvial, tidal, sediments and glacier outwash deposits. The cause of this advance is related to the advance phase of the "tidewater glacier cycle". A 19th century calving retreat resulted in a high area accumulation ratio (AAR) during most of the 20th century (~ 0.90). The high AAR and gradual diminishment of calving due to infilling of the fjord by glacial and fluvial sediments resulted in a positive net balance for several decades, driving the current advance 7 kilometers (km) since 1890. Taku Glacier therefore presents an ideal setting and rare opportunity for the study of slow glacier advance onto and into soft sediments. Continued thickening of ice in the terminus region indicates this advance should continue over the next several years. Reconnaissance observations have documented contemporaneous deformation of proglacial sediments about 200 meters (m) in front of the terminus and prominent bulges up to 10 m high have formed in the compressed sediments with buckling of the overlying soil and vegetation. The Principal Investigators will study the dynamics of the advancing glacier terminus and investigate the effects of this advance on the proglacial geomorphology. Surface velocities, strain rates, and surface elevation changes will be measured both on the glacier terminus and on proglacial features, along with measurements of changes in terminus position. Ground penetrating radar (GPR) and radio echo sounding (RES) will be used to define the glacier geometry and the nature of the bed. They will repeat RES surveys to investigate ongoing subglacial sediment excavation and entrenchment. GPR will also be used to develop a 3-dimensional picture of the structure of the proglacial sediments and their deformation. Existing and new markers on the sediments will measure motion and strain. A key feature of this study will be simultaneous measurement of short-term changes in terminus ice speed and proglacial sediments using precision GPS over several months. Terminus dynamics and the mass balance are integral parts of glacier response theories, but they are poorly understood. The Principal Investigators will use finite element analyses to investigate the deformation and stress fields in the terminal ice wedge and of the sub- and proglacial sediments, using strain data and geometry as constraints. Their aim is to understand the detailed dynamics of terminus advance and the rheological properties of the sediments and the ice near the terminus. They will also investigate the relation between glacier thickening and terminus advance, using our continuing airborne altimetry and photogrammetric measurements of surface elevation.