ALBERT

Description: Natural geological accumulations of carbon dioxide occur widely throughout Europe, often close to population centres. Some of these CO2 deposits leak, whereas others are sealed. Understanding these deposits is critical for selecting and designing underground storage sites for anthropogenic CO2. To provide confidence that the potential risks of geological CO2 storage are understood, geologists are required to predict how CO2 may behave once stored underground. Natural CO2 accumulations provide a unique opportunity to study long-term geochemical and geomechanical processes that may occur following geological storage of anthropogenic CO2. In addition, natural CO2 springs and gas vents can provide information on the mechanisms of gas migration and the potential effects of CO2 leakage to the surface. This paper provides a description of some natural, European CO2 occurrences. CO2 accumulations occur in many basins across Europe. In addition, volcanic areas and seismically active areas allow CO2-rich fluids to migrate to the near surface. Many of these occur in areas that have been populated for hundreds and thousands of years. Stratigraphic traps have allowed CO2 to accumulate below evaporite, limestone and mudstone caprocks. Comparisons between reservoir sandstone and equivalent nearby sandstones that contain no CO2 indicate that reservoir sandstones may experience increased secondary porosity development through feldspar dissolution. Where fracture reactivation allows CO2-rich fluids to migrate, limited self-sealing may take place through calcite precipitation. Gas migration experiments indicate that, due to geochemical interactions, fine-grained seals would be able to trap smaller volumes of CO2 compared to, for example CH4. In natural systems most leakage from depth occurs along fractures and is typically extremely localized on a metre-scale.

Description: The 1920s-1930s debates over the origin of the Channeled Scabland' landscape of eastern Washington, northwestern USA, focused on the cataclysmic flooding hypothesis of J Harlen Bretz. During the summer of 1922, Bretz began leading field parties of advanced University of Chicago students into the region. In his first paper, published in the Bulletin of the Geological Society of America, Bretz took special care not to mention cataclysmic origins. However, in a subsequent paper in the Journal of Geology, to the editorial board of which he had recently been added, Bretz formally described his hypothesis that an immense late Pleistocene flood, which he named the Spokane Flood', had derived from the margins of the nearby Cordilleran Ice Sheet. This cataclysm neatly accounted for numerous interrelated aspects of the Channeled Scabland landscape and nearby regions. Nevertheless, the geological community largely resisted Bretz's hypothesis for decades, despite his enthusiastic and eloquent defence thereof. Resolution of the controversy came gradually, initially through the recognition by J. T. Pardee of a plausible source for the flooding: ice-dammed Pleistocene glacial Lake Missoula in northern Idaho and western Montana. Eventually, by the 1960s, the field evidence for cataclysmic flooding became overwhelming, and physical processes were found to be completely consistent with that evidence. The controversy is of philosophical interest in regard to its documentation of the attitudes of geologists toward hypotheses, which illustrate aspects of geological reasoning that are distinctive in degree from those of other sciences.

Description: In central and eastern Europe in the 1970s and 1980s, prevailing economic and political conditions resulted in a rapid closure of many uranium mining and processing activities. These closures have left a long-lived human health impact. In countries and regions of relatively sparse economic resources, it is essential to understand the true significance of arising impacts and the financial consequences of their mitigation. A pilot study performed at a former site of uranium mining in the Slovak Republic illustrates a methodology to evaluate human health and environmental impact. The main findings are:* The former mining site shows complexity typical of an area in which there is diffuse contamination arising from leaching from waste heaps, and uncontrolled discharges from adits into water courses. In particular, significant hazards occur at the sites due to the presence of uranium ore and its progeny at the surface, which may result in radiological exposure via direct irradiation, ingestion and inhalation of dust or radon. * Site characterization considered both traditional areas of sampling and analysis (rock, soil, dust, radon and water) and identification of those activities and groups or individuals directly or potentially affected by exposure to contamination at the site. These ranged from workers occupying offices and workshops on one of the waste rock heaps, to house builders using waste rock (and potentially ore) for construction purposes, to a range of people exposed due to their recreational activities at the sites (hikers, mineral collectors, rock climbers and gatherers of wild produce). * Historical recultivation measures performed at the site in the 1980s were generally ineffective at curtailing the whole range of radiological hazards. Measures were taken at most sites to bury exposed ore to minimize external irradiation. However, in those cases in which recultivation of heaps was successful, it did little to reduce the impact of radon emanation. Instead, recultivation appeared to have the surprising consequence of reducing the potential dose to the public, via an unrelated route, by making waste rock/ore more difficult to remove for the purpose of construction. * When the importance of all the hazards were ranked, the most significant risk factor arose from inhalation of radon emanating from foundations built from waste rock material. * Of all of the liabilities, a partially water-filled waste rock pit resulted in the highest dose rates. When time spent at this relatively remote site was taken into account, the potential doses received remained to be comparatively high. The most at risk groups were those working, in buildings, on the waste rock heaps and those people who have removed waste rock/ore for building purposes. * Mitigation measures to reduce doses experienced by the exposed groups can be summarized as:-- prevention of the use of waste rock material for the purpose of house building; -- reducing the overall accessibility to the sites, using barriers; -- restricting the recreational value of the sites, by placement of warning signs/fencing (short term); -- relocation of offices and laboratories on the heaps or improvement of the overall ventilation of the working areas.

Description: Water diffusion experiments were performed on a trachytic melt from the Agnano-Monte Spina explosive eruption (Phlegrean Fields, South Italy). Experiments were run in a piston cylinder apparatus at 1 GPa pressure, at temperatures from 1373 to 1673 K and for durations of 0 to 255 s, using the diffusion-couple technique. Water concentration profiles were measured by Fourier transform infrared spectrometry. Water diffusion coefficients at different temperatures and water concentrations were calculated from the total water profiles, using the Boltzmann-Matano technique. Over the investigated range of temperatures and water concentrations, the diffusivity of water in potassic melts (Dwater), m2/s can be described by Arrhenius equations that can be generalized for water concentrations between 0.25 and 2 wt% as follows: [IMG]fd1.gif" ALT="Formula" BORDER="0"〉 where CH2O is the water concentration in wt%, R is 8.3145 (J K-1 mol.-1) and T is the temperature in Kelvin. Water diffusivities in trachytic melts were compared with water diffusivities in rhyolitic and basaltic melts. The activation energies for water diffusivity in trachyte and basalt are comparable, and higher than the haplogranitic melt. This results in a convergence of water diffusion coefficients in all melts at lower (magmatic) temperatures.

Description: The New Zealand American PLUme Mapping Expedition (NZAPLUME) provided the first systematic survey of chemical emissions along a submarine volcanic frontal arc. Chemical plumes emanated from seven of 13 volcanoes that line a 260 km-long section of the southern Kermadec arc northeast of New Zealand. Hydrothermal plumes ranged in depth from 〈200 to 1500 m and are generally more shallow than plumes over mid-ocean ridges (MORs). The chemical signatures of plumes along the southern Kermadec arc are unusually diverse and have concentration anomalies for CO2, H2S and Fe that can exceed those for MOR settings by 5-10 times, or more. Projected end-member fluid concentrations of carbon and sulphur gases at some volcanoes require a magmatic vapour source, while unusually high Fe concentrations and Fe/Mn values are consistent with venting an iron-rich magmatic brine. Thus, vent-fluid emissions on the Kermadec arc volcanoes often appear as hybrid mixtures of hydrothermally evolved sea water influenced by water-rock reaction with compositionally diverse arc lavas, and exsolved magmatic fluid present as gaseous (CO2 and SO2+H2S) and liquid (Fe-rich brines) components. While rock-buffered fluids in arc settings are expected to vary compositionally from one another and from MOR fluids, it is the magmatic components that clearly differentiate arc emissions as being super-enriched in sulphur gases and ionic metals. These first systematic observations of spatially frequent and chemically robust fluid emissions from southern Kermadec arc forecast arcs as being a potentially important source of chemicals to the oceans.

Description: Hydrothermal activity on submarine volcanic arcs in the western Pacific Ocean is known but mostly unexplored. In March 1999, the New Zealand American PLUme Mapping Expedition (NZAPLUME) cruise conducted the first systematic exploration of hydrothermal venting along a sizeable section of an intra-oceanic arc, visiting 13 volcanoes along 260 km of the southern Kermadec arc, just northeast of New Zealand. Conclusive evidence of hydrothermal plumes exists for seven of the 13 volcanoes; at two other volcanoes plume indications were weak and uncertain. The hydrothermal origin of the particle plumes was confirmed by positive anomalies in the ratios of sulphur, iron and copper to titanium relative to non-plume particles, in mass concentrations similar to particles collected from hydrothermal plumes over mid-ocean ridges. The spatial density of active sites along the southern Kermadec arc is at least 2.7 per 100 km (2.7/100 km), probably not significantly different from the weakly constrained value of c. 1/100 km on slow- and intermediate-rate mid-ocean ridges. An analysis of the number of hydrothermal fields produced for the magma delivery rate in each of these environments suggests that the southern Kermadec arc presently has relatively abundant hydrothermal activity. While this result cannot yet be generalized to other Pacific arcs, submarine volcanoes may contribute significantly to the global hydrothermal budget.