In the last few years, several highly retrograde landslides have occurred in northern Quebec, in the marine deposits of the Tyrrell Sea. The landslides in question are flowslides, which can mobilize large masses of partially or totally remoulded soil. The increase in the occurrence of this type of phenomenon along James Bay and Hudson Bay raises several questions about the causes behind these flows and the areas potentially at risk. 

First, the project aims to provide a general overview of flow slides that have occurred in marine deposits in the Tyrrell Sea, particularly along targeted rivers. Rivers such as the Nottaway, Broadback, Rupert, Pontax, and Eastmain, all flowing into James Bay, as well as the Great Whale River, Small Whale River, and their tributaries, all flowing into Hudson Bay. In addition, a more in-depth study of the flow slides that occurred near Waskaganish, along the Rupert River, will be conducted to better understand the cause of the sensitivity of these deposits and to gain a better understanding of the areas susceptible to flows.

First, the sites under study are flowslides concentrated along various rivers flowing into James Bay (Nottaway, Broadback, Rupert, Pontax, and Eastmain) and Hudson Bay (Great Whale River, Small Whale River, and their tributaries). These sites will be studied primarily using geospatial data and aerial photographs to enable a geomorphological and multi-date analysis of the targeted sites. On the other hand, the Rupert River site for this study is mainly concentrated on the left bank of the last 20 kilometers of the river, before it flows into Rupert Bay, in front of the community of Waskaganish. This site will be the subject of a geotechnical characterization.

The geomorphological analysis will be carried out with geospatial data, using a GIS. This analysis is done remotely and does not require a site visit. The geospatial data will be analyzed in order to compile morphological data for the selected sites. For geotechnical characterization in the field, a geotechnical investigation campaign was already carried out by the MTMD in 2024, during which the site was surveyed using geotechnical drilling, piezocones, shear vane tests, and piezometric installations. Ambient vibrations will also be measured using a triaxial seismometer, and potentially an electrical resistivity survey will be conducted to quantify the chlorinated ions present in the marine deposits. Another part of the geotechnical characterization will be carried out in the laboratory. In this part, several parameters of the existing soils will be measured using standardized tests and procedures.

For geomorphological analysis, the expected results are mainly local, or even regional, tendencies in the measurements of flow slides. For geotechnical characterization, the expected results are measurements that provide information on the properties of the soils. Differences in various parameters are expected, which will explain the groupings of flow slides, their shapes and their causes.