Mechanical Properties of Rock Salt from the Klodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Klodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Cold seep formation from salt diapir-controlled deep biosphere oases.

Deep sea cold seeps are sites where hydrogen sulfide, methane, and other hydrocarbon-rich fluids vent from the ocean floor. They are an important component of Earth's carbon cycle in which subsurface hydrocarbons form the energy source for highly diverse benthic micro- and macro-fauna in what is otherwise vast and spartan sea scape. Passive continental margin cold seeps are typically attributed to the migration of hydrocarbons generated from deeply buried source rocks. Many of these seeps occur over salt tectonic provinces, where the movement of salt generates complex fault systems that can enable fluid migration or create seals and traps associated with reservoir formation. The elevated advective heat transport of the salt also produces a chimney effect directly over these structures. Here, we provide geophysical and geochemical evidence that the salt chimney effect in conjunction with diapiric faulting drives a subsurface groundwater circulation system that brings dissolved inorganic carbon, nutrient-rich deep basinal fluids, and potentially overlying seawater onto the crests of deeply buried salt diapirs. The mobilized fluids fuel methanogenic archaea locally enhancing the deep biosphere. The resulting elevated biogenic methane production, alongside the upward heat-driven fluid transport, represents a previously unrecognized mechanism of cold seep formation and regulation.

Emplacement and associated sedimentary record of the Jurassic submarine salt allochthon of the Wurzeralm (Eastern Alps, Austria).

A fossil salt sheet emplaced in the Jurassic in submarine conditions is described in the Eastern Alps of Austria, providing unique insights into the emplacement of similar submarine structures and their potential control on depositional systems. The salt sheet is a plug-fed extrusion emplaced due to squeezing of a salt diapir under compression. The preserved mylonitic shear fabric in the evaporites indicates radial, south-directed emplacement of the salt sheet. Tectono-sedimentary relationships record the evolution of the salt structure, from initial diapiric growth, to salt sheet extrusion and posterior collapse. Syn-extrusion sediments record the variable bathymetry of the extruding salt sheet, with reefal carbonates building up on the crestal bulge while their deeper water equivalents accumulated on the extruding salt lobe. This is the first description of a salt allochthon still linked to its source diapir in the Eastern Alps.

Mechanism of the historical and the ongoing Vulcanian eruptions of Ebeko volcano, Northern Kuriles.

Ebeko is one of the most active volcanoes of the Kurile island arc, producing frequent mild Vulcanian explosions with eruption clouds up to 5 km high. The volcano poses a serious threat to the Severo-Kurilsk town with a population of around 2500 inhabitants, located at a distance of only 7 km on a fan of the volcano's laharic deposits. Here, we report an overview of the activity of the volcano in the 20th-21st centuries and the results of our geological and petrological investigations of the ongoing Vulcanian eruption that started in 2016. We have found that eruptions of Ebeko span a range of mechanisms from purely magmatic to phreatic/hydrothermal. Three of its historical eruptions (the 1934-1935, 1987-1991, and the 2016-ongoing) involved fresh magma, while during the others (1967-1971, 2009-2011) fresh magma was not erupted. Juvenile material of the ongoing eruption represents highly crystalline and highly viscous (more than 108 pa s) low-silica (56-58 wt% SiO2) andesite. Historical data and our observations of the ongoing eruption allowed us to suggest a functional model of the volcano where Vulcanian explosions are caused by shallow intrusions of small diapir-like batches of strongly crystallized and highly viscous andesitic magma ascending into water-saturated, hydrothermally altered rocks composing the volcano summit. We suggest that the diapir's ascent is governed by their positive buoyancy. Some of the diapirs reach and breach the ground surface producing magmatic eruptions of Ebeko, while the others are stuck at the shallow subsurface level and feed intensive hydrothermal activity as well as phreatic eruptions of the volcano. Positive buoyancy of the diapirs is too weak to allow them to extrude high above the ground surface to form lava domes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00445-020-01426-z.

The structure of the Hallstatt evaporite body (Northern Calcareous Alps, Austria): A compressive diapir superposed by strike-slip shear?

Based on old detailed mining maps and own observations in the Hallstatt salt mine, we reinterpret the structure of the Hallstatt evaporite body of the Upper Permian to Lower Triassic Haselgebirge Fm. within the Northern Calcareous Alps (NCA). The Haselgebirge Fm. represents a rocksalt mylonite with abundant lenses of sulphates, mudstones and limestones. In comparison to published results of analogue modeling we interpret the present shape of the Hallstatt body as a WNW-ESE elongated compressive teardrop-like diapir. This is overprinted by NNE-SSW shortening and dominantly sinistral shearing along a W-trending shear zone. The internal structure shows steeply dipping rock units and foliation. Earlier dextral ductile shear fabrics of likely late Early Cretaceous age are preserved in sulphate rocks and are subsequently overprinted by mylonitic fabrics in rocksalt and cataclastic fabrics in other rocks. The low strength of halite results in recent subvertical shortening and a strain rate [Formula: see text] of 8 × 10-10 [s-1] is deduced from deformed subhorizontal boreholes. This value is similar to such strain rates (10-10 to 10-9 s-1) estimated by the halite grain size distribution from other salt mines in the NCA and thus indicative of sub-recent formation of the halite microfabrics.