Abstract
Seabed data acquired from the Hola glacial trough off Vesterålen, North Norway, reveal the morphology of spectacular sandwave fields and large sandwaves in great detail. The sandwave fields are among the deepest known, occurring in water depths of 200–260 m. Multibeam bathymetry and backscatter, shallow seismic, sediment samples and video data collected by the MAREANO programme and bottom current modelling results have been used to interpret morphology, transport and distribution of the seabed sediments. Sand supply to the Hola trough was initially from wave and current reworking of glacial and glaciomarine deposits during the eustatic sea level lowstand and sea level rise after the last glaciation. More recently deposited bioclastic sand dominates the upper part of the sand unit, which locally reaches 10 m thickness. Sand predominantly accumulates behind ridges, where current strength decreases, and in topographic lows. Straight-crested and barchan-type sandwaves up to 3 km long and 7 m high are interpreted to form by tidal and geostrophic currents with bottom current speeds reaching 0.7–0.8 m s− 1. A large cluster of coral reefs occur immediately east of the barchan-type sandwaves, where modelling shows bottom current velocities up to c. 1 m s− 1. Sandwaves occur in four major sandwave fields. Strong variation in the nature of sandwaves over short distances, e.g., migration direction, between neighbouring sandwave fields point to important local variations in current regime and sedimentary processes. The present work demonstrates how local topography and interaction of several current systems may produce complex depositional patterns on a local scale. Detailed multibeam mapping and video inspection of open shelf troughs in other narrow shelf settings worldwide may reveal similar sandwave fields.