Tidally generated sea-floor lineations in Bristol Bay, Alaska, USA

Highly reflective linear features occur in water depths of 20-30 m in north ern Bristol Bay (Alaska, USA) and are, in places, over 600 m in length. The ir length-to-width ratio is over 100.1. The lineations are usually characte rized by large transverse ripples with wavelengths of 1-2 m. The lineations trend about N60 degrees E, and are spaced between 20 and 350 m. Main tidal directions near the lineations are N60 degrees E (flood) and S45 degrees W (ebb), which are parallel to subparallel to the lineations. They suggest t hat the lineations may be tidally generated. The lineations may be bright s onar reflections from a winnowed lag concentrate of coarse sand.