Seismic images and sediment core data from the Bear Island and Isfjorden fans localized along the Svalbard-Barents Sea continental margin, reveal an interesting depositional system consisting of stacked debris flow lobes. The frequent release of debris flows was associated with large volumes of sediment rapidly delivered to the shelf break during periods of maximum glaciation. The compositions of the lobes for both fans are similar, consisting of mainly clay and silt. The data show, however, a dramatic difference in runout distances for the two areas. Isfjorden debris lobes are 10-30 km in length whereas Bear Island lobes are 100-200 km in length. Even more intriguing is the fact that the large runout distances on the Bear Island fan occurred on slopes less than 1° whereas the Isfjorden fan flows occurred on slopes greater than 4°. Depth-averaged non-linear one-dimensional equations for balance of mass and linear momentum are applied to simulate the subaqueous debris flow. The equations are solved by the numerical model BING, describing the flow as a visco-plastic Bingham fluid. The model is employed to study the effect yield strength, viscosity and bathymetry have on debris flow runout. The study shows that the large runout distances can be achieved on the Bear Island fan by visco-plastic flows with sufficiently low yield strength. High yield strength sediments require an additional mechanism, such as hydroplaning, to reach measured runout distances. Most importantly, this study shows the necessity of good rheological measurements for accurate numerical modeling of subaqueous debris flows.
Bibliographical noteFunding Information:
Funding for this research was provided by EU program ENAM II (MAS3-CT95–003) and the Seabed/Norsk Hydro project. The authors thank Dieter Issler and Gary Parker for their support and review of this work. We would also like to thank Lincoln Pratson and two anonymous reviewers for their constructive reviews of this manuscript. A free copy of the numerical model BING can be obtained from the St. Anthony Falls Laboratory web site: www.umn.edu/safl .
- Debris flow
- Gravity flow