Evolution of an anthropic source-to-sink system: Wabush Lake

Abstract

Wabush Lake is one of the few very well-constrained source-to-sink sedimentary systems in the world that exhibits near-continuous turbidity currents. In this system, approximately 20million tons of mine tailings are delivered each year to a 40km2 lake. Multibeam bathymetric surveys of this lake were carried out between 1999 and 2011. In addition, a program of extensive sampling and seismic surveys, an airborne LiDAR survey and a photogrammetric survey were carried out during this period. The objective of this study was to determine the evolution through time of this anthropic source-to-sink system, from the point where sediments exit the slurry pipelines at the head of the system to the distal end and bottom of the Lake. The total volume of the Lake is around 1×109m3.Analysis of subaerial and subaqueous datasets allows the evaluation of disposal strategies on the delta topset and on tailings accumulation. Disposal strategies influence the dynamics of the channels on the topset, thus in turn affecting the accumulation of tailings throughout the lake, as well as the shoreline advancement rate. Subaqueous erosional channels present on the bed of the Lake influence the depositional pattern of tailings as well as their granulometric distribution. These erosional channels are created by the shoreward migration of knickpoints. In some places, this migration can be documented over multiple surveys.Finally, sequential analysis of the 1999, 2004, 2006, 2008 and 2011 surveys has allowed detailed documentation of the infilling of the Lake, including the migration of sediment depocenters, the mechanism of emplacement and the progressive infilling of a series of minibasins.