Impact of glacially induced stresses and strains at Canadian candidate sites for nuclear waste disposal

Abstract

Continental-scale glaciations lead to deformation, geopotential, rotation, and stress changes of the Earth. Especially glacially induced stress changes in the lithosphere can significantly impact potential nuclear waste repository sites, planned for depths a few hundred meters below ground. Ensuring the long-term stability of these sites warrants analyzing such additional stresses in the crust that might be imposed by future ice sheets during forthcoming glaciations. We focus on North America by investigating the past to quantify such stresses. Utilizing a refined, high-resolution North American ice history spanning 122,000 years from the University of Toronto Glacial Systems Model, alongside various one- and three-dimensional earth structures, we investigate the dynamic nature of glacially induced stresses at Canada’s candidate sites South Bruce and Ignace. Both sites are situated in Ontario but 1000 km apart. Additionally, we examine the corresponding deformation and strain changes. We find that both sites undergo strong variations in glacially induced stresses and strains over a glacial cycle. Especially the horizontal components can change from tensional to compressive within a few thousand years due to fluctuations in ice cover. Surprisingly, despite South Bruce's location farther from the ice sheet center and its temporary position in the forebulge of the ice sheet, stress and strain magnitudes resemble those of Ignace. Moreover, there's potential at South Bruce for altering the direction of pre-existing maximum horizontal stress. Interestingly, the choice of earth structure in the modelling affects strain more than stress. Although the sites are 1000 km apart, our results do not indicate a superior repository site. Instead, they emphasize the need to integrate our findings into the site selection process and barrier integrity assessment. We recommend further studies focusing on a stress analysis with more detailed earth models, considering faults and lineaments near the candidate sites. This research was funded by the Nuclear Waste Management Organization, Canada.