Morphodynamic and Slope Instability Observations at Wabush Lake, Labrador

Abstract

Since 1964, Iron Ore Company of Canada (IOCC) has deposited iron tailings resulting from mining operations into Wabush Lake, Western Labrador. Bathymetric surveys were carried out between 2004 and 2008 as part of the overall environmental IOCC plans to maintain safe disposal strategies of tailings into the lake. In this paper, we present the evolution in distribution and morphological characteristics over the last 4 years of the tailings overlying lacustrine sediments and bedrock. In 2004, a high definition multibeam survey of Wabush Lake was carried out for the first time and revealed lake floor features, including a fine network of channels and a delta foreslope with well-developed knickpoints. Other features such as older subaqueous mass movement scars and an esker were also identified. The delta foreslope channels, in 2004, led into a deeper long channel connected with the deepest part of the lake where turbidite deposition took place. A second bathymet-ric survey was carried out in 2006. Many of the features seen on the 2004 map were already buried by the advancing delta front. Results indicate that the 2004 channel system was almost completely obliterated with the generation of many new others. Development of the knickpoints is also observed where some are still present and new ones are discovered. A third bathymetric survey conducted in 2008 demonstrates a different spatial arrangement of features. Well developed wider channels and new knickpoints are observed on the foreslope delta. The sequential analysis of 2004, 2006 and 2008 surveys proved to be a useful tool to evaluate: (1) the rate of infilling of the lake, where accumulation took place and by which mechanisms (2) the evolution of the foreslope delta gradient and, (3) the evolution of instability areas. Our results indicate that these recently developed techniques are useful tools for monitoring underwater tailings disposal and stability.