Abstract
The onset of glaciation in the active St. Elias orogeny in southeast Alaska resulted in massive sediment flux to the Gulf of Alaska, but the resulting sedimentary systems of the continental slope remain poorly understood. During glacial periods ice streams advance across the continental shelf, carving troughs that reach the shelf edge and route sediment to the continental slope and deep sea fan systems.

High-resolution multi-beam data is used to develop the relationship between the Yakutat and Alsek Sea Valleys and the resulting continental slope morphology. The shelf and slope geomorphology can be divided into statistical groupings that relate to the relative balance of erosion and deposition. Our analysis shows that only the paleo-ice stream eroding the heart of the St. Elias orogen has been able to build an incipient Trough-Mouth Fan. The massive sediment supply from this region was able to overwhelm the steep initial topography of the transform margin, while further to the east sediment slope-bypass dominates.

This analysis provides an extreme end member to existing studies of temperate glaciation along continental margins. The unique interplay between rapid uplift due to ongoing collision and the massive erosion caused by temperate glaciers provides for sedimentary flux far above most other systems. This sediment supply allows for formation of progradational trough mouth fans in a system that is otherwise completely unfavorable to slope deposition and progradation.