MORPHOLOGY AND MORPHOGENESIS OF A HIGH-LATITUDE CANYON; THE ANDøYA CANYON, NORWEGIAN SEA

Abstract

The morphology of the high-latitude Andøya Canyon in the Norwegian Sea was studied using multi-beam bathymetry data. The canyon excavation processes include sliding and slumping, axial incision and gullying. Sliding and slumping has most frequently occurred in muddy sediments of the western sidewall due to canyon axial incision and undercutting, and failures during infilling of a high-relief terrain by alongslope transported sediments. Axial incision is inferred to be due to turbidity current erosion, the turbidity currents were mainly the result of piracy of shelf sediments. The eastern sidewall is dominated by gullies speculated to be the initial forms generated on a steep slope constructed from stiff, poorly sorted glacigenic sediments. From the present canyon morphology including the overall convex-upwards form of the topographic long-profile with a steep (20–25°) upper headwall, we favour a “bottom-up” canyon development, i.e. mass wasting and subsequent piracy of alongslope transported slope and shelf sediments. In contrast to most other canyons, the development of the Andøya Canyon was not only a result of side- and headwall instability and axial incision, most active during periods of high sediment transfer, but also due to infilling of the canyon by sediments transported by alongslope flowing ocean currents and from the Fennoscandian Ice Sheet at the shelf break. There are little or no slide deposits covering the thalweg. This leads us to suggest that the most recent process dominating within the canyon is turbidity current flushing and erosion, inferred to have occurred during the Holocene.