Volcanic and Tectonic Hazard Assessment for Nuclear Facilities: The impact of subsidence, uplift and erosion on geological repositories for radioactive wastes

Earth is a dynamic planet and all points on the land surface are subject to processes that cause either uplift or subsidence. These types of vertical movements can vary considerably in magnitude and can occur on a wide range of timescales. Short-term cyclic motions, caused by planetary orbits, range from minute daily movements due to gravitational effects (Earth tides) through larger, millennial-scale effects of glacial loading or unloading and sea-level variations caused by climate changes driven by Milankovitch variations in Earth's movement around the Sun, or other mechanisms. Over a longer timescale, tectonic processes resulting from plate-motion-driven crustal deformation and the emplacement and evolution of magma bodies cause more significant movements. For completeness, we should note that a further series of processes may need to be considered, where land surfaces rise due to the pressurization of underground reservoirs and sink due to depressurization of fluids or material removal, caused by either anthropogenic or natural processes. Uplift is generally accompanied by erosion of the uplifted surface, with erosion rates dependent on the mechanical and chemical properties of the rocks, climate, altitude and uplift rate; high uplift rates generally correlate with high erosion rates. The corollary is that subsidence is generally accompanied by sedimentation onto the sinking surface, often into basinal structures, with erosion on the flanks of the subsiding area. The fundamental background to the identification and characterization of tectonicallydriven uplift and erosion is presented by Litchfield et al. (Chapter 4, this volume) and the special case of the influence of such processes on coastal sites is discussed by McKinley and Alexander (Chapter 22, this volume).