International FEP List - Version 3
FEP 1.2.5 Magmatic and volcanic activity

The processes and events associated with sub-surface molten rock (magma), and the direct and indirect effects of sub-surface molten rock at the earth’s surface, expressed in volcanoes. These effects may include eruption of molten rock as lava and/or eruption of fragmented rock (pyroclastic activity). Intrusion of molten rock into solid rock in the sub-surface (plutonism) may occur beneath volcanoes or in the sub-surface remote from volcanic activity. A volcano is a vent or fissure in the Earth's surface through which one or more of the following may flow/be expelled: magma; mud; solid and plastic fragments; liquid droplets; and hot gases. Around 95% of active volcanoes occur at lithospheric plate boundaries. The other 5% are associated with lithospheric hot spots and rifts which correspond to weak areas in the Earth’s crust and are caused by plumes of rising magma that have their origin within the asthenosphere. The high temperatures and pressures associated with magmatic and volcanic activity may result in permanent changes in the surrounding rocks (FEP 1.2.6).

Magmatic and/or volcanic activity could influence the performance and safety of a repository by: compromising the integrity of the engineered and / or natural barriers; by influencing the chemical environment in the repository and its environs; and by influencing the characteristics and fluxes of fluids that may flow within and through the repository and surrounding geosphere. Magmatic and volcanic activity could also influence the characteristics of surface and near-surface environments, including the biosphere, in the vicinity of a repository. Thus, magmatic and volcanic activity could affect the types of receptors that could be impacted by any radionuclides or other contaminants that leave a repository during the post-closure period.

Moving magma in the subsurface could impact directly upon a repository that is sited sufficiently close to a centre of magmatic activity. Direct effects on a repository might include intersection of repository rooms by an igneous dike. Additionally, magma would impact upon geothermal gradients, even at some distance from the magma itself. Modified geothermal gradients could in turn cause convection of groundwater (hydrothermal activity), other fluids in the subsurface. The modified geothermal gradient would also impact upon chemical reactions between these fluids and wastes, engineered barriers and rock. Certain magmas could themselves be sources of water and gases. Moving magma and / or the associated movements of other fluids could cause creation, activation and sealing of faults, which in the vicinity of a repository could potentially act as pathways for the migration of radionuclides and other contaminants. Flowing magma and/or associated fluids that intersect the repository and that also reach the surface may give rise to dispersion of wastes in a plume of volcanic ejecta and in lava flows. Magmatism and volcanic activity could be accompanied by changes in topography, changes in rock stress and rock deformation. These changes could be sudden (e.g. volcanic caldera collapse) or more gradual (e.g. regional uplift). Volcanic activity could lead to unloading or loading of rocks, by ejection of rock or deposition of ejecta or lava respectively, even at considerable distances (many tens or even hundreds of kilometres) from the volcanic centre. Magmatic and volcanic activity are closely related to seismicity (FEP 1.2.4).