Holocene sediment production and sediment volume partitioning in western Norwegian fjord-valley source-to-sink systems

William Helland-Hansen (UiB), Christian Haug Eide (UiB), Atle Nesje (UiB), Haflidi Haflidason (UiB)

2017 - 2021

The overall aim of this project is to integrate the source-to-sink approach into a modern system in order to gain a better understanding on parameters that influence sediment production and partitioning in recently glaciated fjord-valley systems. 

In order to understand both landscape evolution through time and sediment delivery to lowlands and marine basins, it is important to quantify the amount of sediment produced and remobilized from eroding uplands. Mapping, dating and characterization of post-glacial sediment volumes and accompanying catchment areas in Fjærland will form a basis for developing models for sediment production and sediment partitioning in Western Norway fjord-valley systems. By acquiring data on the age, composition, geometry and volume of marine (fjords) and terrestrial (avalanche fans, lakes, postglacial terraces, floodplains and deltas) sediment sinks one can couple this data against:

• Modern day and historical sediment loads and sedimentation rates in the depositional environment (e.g. measuring sedimentation rates in the fjord and lake sediments, monitoring suspended load and bedload in rivers, and monitoring avalanche activity of selected avalanche fans).
• Catchment parameters such as relief, area, bedrock geology and climatic variations in order to better understand the timing and distribution of components within the sourceto-sink system.

Studies focusing on the quantification of sediments in the combined fjord-valley systems are relatively few. Thus, this research projects aims at contributing more knowledge to understanding the whole fjord-valley system by combining marine and terrestrial data. To successfully do so, the project has the following objectives:

1. Utilize high-resolution digital elevation models (for topography) and Quaternary geological maps (Aa and Sønstegaard, 1995) to understand the catchment properties (basin area, relief, bedrock geology, sediment thickness and distribution) influence on the sediment flux to the fjord-valley system. Apply multibeam bathymetry data in order to map submarine sills (that may have separated the fjord system into several basins), and observe evidence of past avalanches, as well as other areas of interest. Georadar and LiDAR data will further aid in constraining sediment volumes in the terrestrial realm.

2. Map avalanche fans, glaciofluvial and glaciomarine terrace locations in both the field and using GIS/DEM computations. Perform sediment volume calculations on terraces eroded by rivers and measure sedimentation rates of avalanche fans using Drone/LiDAR data (Blikra and Nemec, 1998). 

3. Sediment traps will be placed in the main river in Fjærland in order to measure modern sedimentation rates that will be compared to denudation rates found from testing sediments at river mouths for cosmogenic nuclides (Von Blanckenburg, 2005). Sediment flux data of suspended loads have been attained, and several more samples will be gathered by taking water samples of the river at several locations (in cooperation with Bremuseet, Pål Gran Kielland). This data will be compared to measured sedimentation rates from sediment traps as well as the denudation rates in order to obtain better values. Further on, measured and modern day sediment discharge and water discharge variations will be coupled in order to extrapolate sediment discharge variations for the time-period covered with water discharge data.

4. Use seismic profiles and cores (both marine, lake and possibly terrestrial (on terraces)) in order to estimate modern and historical sedimentation rates:

- Couple fjord sedimentation rates (from dated sediment cores) with modern and historical water discharge variations from the catchment to correlate them with flooding events (Fig. 4) (Bayliss and Reed, 2001). This will help in understanding the contribution of river floods relative to background sedimentation rates in both modern and Holocene sediment volumetrics, and the relative proportion of bedrock eroded and remobilized (late Pleistocene/early Holocene) sediments in flood and non-flood situations. 

5. Assess the applicability of numerical models (such as the BQART model by Syvitski and Milliman (2007)) on recently glaciated fjord-valley catchments. 

6. Contrast sediment production in currently glaciated and non-glaciated catchment areas in order to better understand the controls glaciers impose on sediment production/partitioning.

7. Compare sediment production/partitioning in the Fjærland and Flåm catchments with the results from projects such as SEDITRANS and SedyMONT that focuses on catchments in Nordfjord (SEDITRANS, 2004).