Fjords

Abstract

The term “fjord” has its origin in the Old Norse word “fjorthr” which also included freshwater lakes. However, according to above definition, we will deal here exclusively with deep, semi-enclosed coastal inlets that generally are long relative to their width. Globally, almost all fjords are found at higher latitude, i.e., north of 43° and south of 42°. The longest (>200 km) fjords are Scoresby Sund, East Greenland, and Sognefjord in Norway. The inland termination and seaward opening of the fjord are referred to as head and mouth, respectively. Fjord topography is often characterized by one or more submarine sills representing relict moraines or bedrock ridges. Sediments from fjord basins may provide high-resolution records of both marine and terrestrial environmental changes (Gilbert, 2000), with maximum accumulation rates amounting to more than 1 m per year (Syvitski and Farrow, 1989). Sedimentation patterns in the fjord are controlled by glacial and fluvial conditions, topography, sea-level, and hydrography of coastal waters (Syvitski et al., 1987). Usually, an estuarine circulation regime with a saline, occasionally poorly oxygenated deep layer and a low-salinity surface layer marks the hydrography. In fjords where a tidewater glacier is present, turbid meltwater from beneath the glacier rises as a plume into the surface layer, where flocculation of silt and clay particles leads to settling of these fine-grained particles contributing to the bulk mass of the fjord deposits (Mugford and Dowdeswell, 2011). Lamination may occur due to the effect of seasonal melting on the depositional process. These fine-grained sediments do, however, often display intervals with coarser ice-rafted debris which may reflect changes in iceberg calving activity of the local glacier (Andresen et al., 2012). A common feature of fjord basins with a high sediment input is a wide variety of slope failures along side-wall margins or basement highs and frequent occurrence of turbidites and mass-flow deposits in the adjacent basin. This slope instability implies a potential geohazard risk in the form of a local tsunami.