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Karatson D.,Eötvös Loránd University | Wulf S.,German Research Center for Geosciences | Wulf S.,Senckenberg Institute | Veres D.,Romanian Academy of Sciences | And 13 more authors.
Journal of Volcanology and Geothermal Research | Year: 2016

The most recent, mainly explosive eruptions of Ciomadul, the youngest volcano in the Carpatho-Pannonian Region, have been constrained by detailed field volcanological studies, major element pumice glass geochemistry, luminescence and radiocarbon dating, and a critical evaluation of available geochronological data. These investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of Ciomadul's twin craters (St. Ana and Mohoş) that received tephra deposition during the last eruptions of the volcano. Our analysis shows that significant explosive activity, collectively called EPPA (Early Phreatomagmatic and Plinian Activity), started at Ciomadul in or around the present-day Mohoş, the older crater, at ≥51 ka BP. These eruptions resulted in a thick succession of pyroclastic-fall deposits found in both proximal and medial/distal localities around the volcano, characterized by highly silicic (rhyolitic) glass chemical compositions (ca. 75.2-79.8 wt.% SiO2). The EPPA stage was terminated by a subplinian/plinian eruption at ≥43 ka BP, producing pumiceous pyroclastic-fall and -flow deposits of similar glass composition, probably from a "Proto-St. Ana" vent located at or around the younger crater hosting the present-day Lake St. Ana. After a quiescent period with a proposed lava dome growth in the St. Ana crater, a new explosive stage began, defined as MPA (Middle Plinian Activity). In particular, a significant two-phase eruption occurred at ~31.5 ka BP, producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of Sf. Ana, and followed by pumiceous fallout from a plinian eruption column. Related pyroclastic deposits show a characteristic, less evolved rhyolitic glass composition (ca. 70.2-74.5 wt.% SiO2) and occur both in proximal and medial/distal localities up to 21 km from source. The MPA eruptions, that may have pre-shaped a crater similar to, but possibly smaller than, the present-day St. Ana crater, was followed by a so far unknown, but likewise violent last eruptive stage from the same vent, creating the final morphology of the crater. This stage, referred to as LSPA (Latest St. Ana Phreatomagmatic Activity), produced pyroclastic-fall deposits of more evolved rhyolitic glass composition (ca. 72.8-78.8 wt.% SiO2) compared to that of the previous MPA stage. According to radiocarbon age constraints on bulk sediment, charcoal and organic matter from lacustrine sediments recovered from both craters, the last of these phreatomagmatic eruptions - that draped the landscape toward the east and southeast of the volcano - occurred at ~29.6 ka BP, some 2000 years later than the previously suggested last eruption of Ciomadul. © 2016 Elsevier B.V.

Janovics R.,Hertelendi Laboratory of Environmental Studies | Molnar M.,Hertelendi Laboratory of Environmental Studies | Futo I.,Hertelendi Laboratory of Environmental Studies | Rinyu L.,Hertelendi Laboratory of Environmental Studies | And 4 more authors.
Radiocarbon | Year: 2010

An automatic water sampling unit was developed to monitor the radioactive emission (radiocarbon and other corrosion and fission products) from nuclear facilities into the groundwater. Automatic sampling is based on the principal of ion exchange using built-in resin columns in the submerging samplers. In this way, even the short-term emissions can be detected. According to our experiments, the 14C activity concentrations and the δ13C values of the samples made by the ion exchange method are systematically underestimated compared to the real values. The carbonate adsorption feature of the sampling unit was studied under laboratory and field conditions. For this purpose, a test method was developed. The observed sampling efficiencies and additionally some carbon contamination for the sampling method itself have to be taken into consideration when we estimate the amount of 14C contamination introduced into the groundwater from a nuclear facility. Therefore, a correction factor should be made for the 14C anion exchange sampling. With the help of this correction, the results converge to the expected value. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

Rovni I.,Budapest University of Technology and Economics | Szieberth M.,Budapest University of Technology and Economics | Palcsu L.,Hertelendi Laboratory of Environmental Studies | Major Z.,Hertelendi Laboratory of Environmental Studies | Feher S.,Budapest University of Technology and Economics
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

This paper presents high accuracy tritium production rate measurement results compared with calculations using the MCNPX Monte Carlo particle transport code. The experimental results are regarded as reference values for a new passive technique based on the secondary charged particle activation method developed for measuring the tritium production rate in the test blanket modules of the ITER Tokamak. The 16O(t,n)18F reaction, which is one of the possible tritium monitor reactions, was also extensively investigated, and the experimentally determined reaction rates were compared with simulations. Li2CO3 solution was filled and sealed into quartz ampoules which were irradiated in the Training Reactor of the Budapest University of Technology and Economics. The amount of 18F was determined using γ-spectroscopy. Then the precise tritium measurements were carried out in the Hertelendi Laboratory of Environmental Studies using the 3H-3He ingrowth method, where the 3He produced during the storage time is measured by a static noble gas mass spectrometer (VG-5400). The HT/HTO ratio in the irradiated aqueous solutions was found to be 0.1323±0.0034. Based on the comparison of the measurements and the simulations it was pointed out that the model calculations underestimate the reaction rate of both the Li6(n,t)α and the 16O(t,n) 18F reactions by 5-10% and 15%, respectively. © 2013 Elsevier B.V.

Molnar M.,Hertelendi Laboratory of Environmental Studies | Haszpra L.,Hungarian Meteorological Service | Svingor E.,Hertelendi Laboratory of Environmental Studies | Major I.,Debrecen University | Svetlik I.,Nuclear Physics Institute of Czech Republic
Radiocarbon | Year: 2010

A high-precision atmospheric CO2 monitoring station was developed as a field unit. Within this, an integrating CO2 sampling system was applied to collect samples for radiocarbon measurements. One sampler was installed in the second largest city of Hungary (Debrecen station) and 2 independent 14CO2 sampling lines were installed ~300 km from Debrecen in a rural site at Hegyhátsál station as independent background references, where high-precision atmospheric CO2 mixing ratios have been measured since 1994. Fossil fuel CO2 content in the air of the large Hungarian city of Debrecen was determined during the winter of 2008 using both the measurements of CO2 mixing ratio and 14C content of air. Fossil fuel CO2 was significantly enhanced at Debrecen relative to the clean-air site at Hegyhátsál. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

Molnar M.,Hertelendi Laboratory of Environmental Studies | Major I.,Debrecen University | Haszpra L.,Hungarian Meteorological Service | Svetlik I.,Nuclear Physics Institute of Czech Republic | And 2 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2010

A field unit was installed in the city of Debrecen (East Hungary) during the summer of 2008 to monitor urban atmospheric fossil fuel CO2. To establish a reference level simultaneous CO2 sampling has been carried out at a rural site (Hegyhátsál) in Western Hungary. Using the Hungarian background 14CO2 observations from the rural site atmospheric fossil fuel CO2 component for the city of Debrecen was reported in a regional "Hungarian" scale. A well visible fossil fuel CO2 peak (10-15 ppm) with a maximum in the middle of winter 2008 (January) was observed in Debrecen air. Significant local maximum (~20 ppm) in fossil fuel CO2 during Octobers of 2008 and 2009 was also detected. Stable isotope results are in agreement with the 14C based fossil fuel CO2 observations as the winter of 2008 and 2009 was different in atmospheric δ13C variations too. The more negative δ13C of atmospheric CO2 in the winter of 2008 means more fossil carbon in the atmosphere than during the winter of 2009. © 2010 Akadémiai Kiadó, Budapest, Hungary.

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