Abstract
The site where a peaceful underground nuclear explosion, Crystal, was detonated in 1974, at a depth of 98 m in perennially frozen Cambrian limestones, was studied by electrical resistivity tomography (ERT) in 2019. The purpose of our research, the results of which are presented in this article, was to assess the current permafrost state at the Crystal site and its surroundings by inversion and interpretation of electrical resistivity tomography (ERT) data. Inversion of the ERT data in Res2Dinv verified against ZondRes2D forward models yielded 2D inverted resistivity sections to a depth of 80 m. The ERT images revealed locally degrading permafrost at the Crystal site and its surroundings. The warming effect was caused by two main factors: (i) a damage zone of deformed rocks permeable to heat and fluids, with a radius of 160 m around the emplacement hole; (ii) the removal of natural land cover at the site in 2006. The artificial cover of rock from a nearby quarry, which was put up above the emplacement hole in order to prevent erosion and migration of radionuclides, is currently unfrozen.
Highlights
The impact of underground nuclear explosions (UNE) on the Earth’s crust is the most violent man has ever caused [1]
The slope and river valley inverted resistivity sections differed: layered permafrost was found in the former and high resistivity was identified below the active layer down to 80 m in the latter, with low-resistivity patches near the river
The permafrost in the natural forested slope landscape was found to have a layered resistivity structure controlled by the percentages of clay minerals in limestone
Summary
The impact of underground nuclear explosions (UNE) on the Earth’s crust is the most violent man has ever caused [1]. The extreme heat and pressure of an underground nuclear explosion causes changes in the surrounding rocks: those closest to the source are molten and vaporized, forming a confinement cavity with a hardpan of melt rocks. Zones of crushed and cracked rocks are created [1]. Shallow explosions cause swelling and failure of rocks as upthrust domes that fall back due to gravity. The cavity collapses, and the crushed rocks rise (“float up”), forming a rubble chimney in seconds to hours [1]. The collapsed confinement cavity surrounded by heavily deformed rocks becomes an uncontrolled storage source of special radioactive wastes in the geological environment
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