THE EFFECT OF GLACIAL RETREAT ON FJORD DEPOSITIONAL REGIMES, TAAN FIORD, ICY BAY, ALASKA

Recently acquired multi-channel seismic (MCS) and high-resolution bathymetry data in Taan Fiord, Alaska image the depositional record of sedimentation associated with debuttressing overlying glacial outwash from the retreat of Tyndall Glacier within the last 60 years. Profiles taken adjacent to the fjord wall reveal depositional geometries potentially varying with distance from the retreating ice face of Tyndall Glacier.

Taan Fiord is a glacially eroded inlet to Icy Bay that was once fully overlain by Tyndall Glacier with 400 m of vertical accumulation. Since 1961, Tyndall Glacier has retreated 17 km leaving the fjord walls exposed. Loose sediment along with high angle fjord topography promote landslide events such as the one documented in October 17, 2015. Approximately 180 million tons of material wasted onto the glacial front and into the fjord creating a tsunami with a 184 m runup. The tsunami was detected 155 km away and leveled vegetation as it migrated out into Icy Bay. Previous studies suggest the possibility of future tsunamis of greater impact and documentation of previously unrecorded landslide depositional events are relevant for projection of future landslides.

Preliminary time migrated stacks show a sediment accumulation in the fjord basin representative of debuttressing from the fjord walls. The marine geophysical profiles could be key in distinguishing the range of debuttressing sedimentation, ranging from alluvial runoff to large mass-wasting, and how these processes vary with time and distance from the ice front.