Cascades and plunge pools on the continental slope of the Gulf of Alaska

Abstract

More than 321 400 km2 of seafloor in the Gulf of Alaska was mapped in 2005 (Gardner & Mayer 2005). Both bathymetry and high-resolution backscatter data were collected from the R/V Kilo Moana . The resulting digital terrain models and backscatter mosaics provide a remarkable view of the processes on a tectonically active, glaciated margin. In the course of these surveys several morphological features, similar to cascades and plunge pools found beneath terrestrial waterfalls, were identified on the continental slope. Although several cascade-like features are seen along the continental slope of the southeastern Alaskan margin, the most prominent is found SW of Yakutak Bay and south of the Malispina Glacier which emanates from the St Elias Mountain Range (Fig. 1a, b). The St Elias Range includes some of the highest mountains in North America with remarkable vertical relief, for example Mount St Elias rises to 5489 m above sea level in less than 16 km horizontal distance (Fig. 1a, b). Offshore of Yakutak Bay is the Yakutak Valley, a large, glacially excavated, submarine valley that cuts NE–SW across the continental shelf. Yakutak Valley originates in Yakutak Bay with a width of approximately 50 km and a depth of 120 m as it reaches the shelf break 90 km from the mouth of the bay (Fig. 1a). Fig. 1. Multibeam bathymetry and backscatter along the SE Alaskan margin. ( a …