Quantitative morphologic analysis of the Gulf of Alaska Yakutat margin: evidence for recent trough mouth fan growth

Abstract:

Glaciated continental shelves are host to numerous morphologic features that help understand past glacier dynamics. Southeastern Alaska is home to the St. Elias Mountains, an active orogen being impacted by temperate marine glaciers. During glacial periods ice streams advance across the continental shelf, carving shelf-crossing troughs that reach the shelf edge. We use high-resolution multibeam data to develop the relationship between two troughs, the Yakutat and Alsek Sea Valleys, and associated 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 indicates that only the Yakutat system has been able to build an incipient trough-mouth fan. The extreme sediment supply from this region was able to overwhelm the steep initial topography of the transform margin, while farther 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 in a coastal system with extremely high precipitation provides for sedimentary flux far greater than other systems and thus allows for formation of a trough mouth fan in spite of a tectonically generated steep slope.