Shallow velocity model of the Northern Flank of Stromboli Volcano, deduced by high frequency surface wave dispersion

The wavefield produced by the Stromboli volcano explosion quakes shows a significant amount of surface waves. Rayleigh waves recorded by a linear array have been investigated to infer the shear-wave velocity model of the Stromboli northern flank. The group velocity dispersion curve was obtained using the multiple filter technique, while the phase velocity dispersion curve was calculated both by phase-matched filtering and performing a p– stack on the observed waveforms. Through the inversion of these curves we were able to recover the shear-wave structure to a depth of about 190 m.     

Naturally occurring radionuclides and their geochemical interactions at a geothermal site in the North German Basin

The activities of the most common, naturally occurring radionuclides ²³⁸U, ²²⁶Ra, ²¹⁰Pb, ²²⁸Ra, ²²⁸Th, and ⁴⁰K were measured by gamma-ray spectrometry in samples from reservoir rocks, geothermal fluids, and mineral precipitates at the geothermal research site Groß Schönebeck (North German Basin). Results demonstrated that the specific activity of the reservoir rock is within the range of the mean concentration in the upper earth crust of <800 Bq/kg for ⁴⁰K and <60 Bq/kg for radionuclides of the ²³⁸U and ²³²Th series, respectively. The geothermal fluid showed elevated activity concentrations (up to 100 Bq/l) for ²²⁶Ra, ²¹⁰Pb, and ²²⁸Ra, as compared to concentrations found in natural groundwater. Their concentration in filter residues even increased up to 100 Bq/g. These residues contain predominantly two different mineral phases: a Sr-rich barite (Sr, BaSO₄) and laurionite (PbOHCl), which both precipitate upon cooling from the geothermal fluid. Thereby they presumably enrich the radionuclides of Ra (by substitution of Ba) and Pb. Analysis of these precipitates further showed an increased ²²⁶Ra/²²⁸Ra ratio from around 1–1.7 during the initial months of fluid production indicating a change in fluid composition over time which can be explained by different contributions of stimulated reservoir rock areas to the overall produced fluid.     

Halogen-dominant mineralization at Mt. Calvario dome (Mt. Etna) as a response of volatile flushing into the magma plumbing system

The exceptional occurrence of fluorine-rich mineral phases in the benmoreitic lava dome of Mt. Calvario (south-western flank of Mt. Etna) has given the opportunity to understand the genetic process allowing their crystallization. Both primary and secondary mineral associations were found, namely: plagioclase, clinopyroxene, olivine, fluorapatite and iron oxides as primary assemblage, whereas fluoro-edenite and fluorophlogopite, ferroan-enstatite, hematite, pseudobrookite and tridymite as secondary mineralization. In addition to some major and trace elements (e.g., Fe, Ti, Na, K, P, Ba, Rb, Sm, Zr), particularly fluorine and chlorine concentrations of the whole rock are significantly higher than other Etnean prehistoric benmoreites, and cannot be accounted for common differentiation processes in the feeding system. The selective enrichment in some elements has been here attributed to volatile flushing occurring in the plumbing system, with fluid/melt ratio of ~0.65:1. The resulting high amount of fluorine, coupled with its high solubility even at low pressure for benmoreitic melts, finally led to nucleation and growth of F-rich mineral phases during syn- and post-eruptive conditions.     

Representivity of incompletely sampled fall deposits in estimating eruption source parameters: a test using the 12–13 January 2011 lava fountain deposit from Mt. Etna volcano,Italy

The Southeast Crater (SEC) of Mt. Etna, Italy, is renowned for its high activity, mainly long-lived eruptions consisting of sequences of individual paroxysmal episodes which have produced more than 150 eruptive events since 1998. Each episode typically forms eruption columns followed by tephra fallout over distances of up to about 100 km from the vent. One of the last sequences consisted of 25 lava fountaining events, which took place between January 2011 and April 2012 from a pit-vent on the eastern flank of the SEC and built a new scoria cone renamed New Southeast Crater. The first episode on 12–13 January 2011 produced tephra fallout which was unusually dispersed toward to the South extending out over the Mediterranean Sea. The southerly deposition of tephra permitted an extensive survey at distances between ~1 and ~100 km, providing an excellent characterization of the tephra deposit. Here, we document the stratigraphy of the 12–13 January fallout deposit, draw its dispersal, and reconstruct its isopleth map. These data are then used to estimate the main eruption source parameters. The total erupted mass (TEM) was calculated by using four different methodologies which give a mean value of 1.5?±?0.4?×?10⁸ kg. The mass eruption rate (MER) is 2.5?±?0.7?×?10⁴ kg/s using eruption duration of 100 min. The total grain-size (TGS) distribution, peaked at ?3 phi, ranges between ?5 and 5 phi and has a median value of ?1.4 phi. Further, for the eruption column height, we obtained respective values of 6.8–13.8 km by using the method of Carey and Sparks (1986) and 3.4?±?0.3 km by using the methods of Wilson and Walker (1987), Mastin et al. (2009), and Pistolesi et al. (2011) and considering the mean value of MER from the deposit. We also evaluated the uncertainty and reliability of TEM and TGS for scenarios where the proximal and distal samples are not obtainable. This is achieved by only using a sector spanning the downwind distances between 6 and 23 km. This scenario is typical for Etna when the tephra plume is dispersed eastward, i.e., in the prevailing wind direction. Our results show that, if the analyzed deposit has poorer sample coverage than presented in this study, the TEM (3.4?×?10⁷ kg) is 22 % than the TEM obtained from the whole deposit. The lack of the proximal (<6 km) deposit may cause more significant differences in the TGS estimations.     

The altitudinal temperature lapse rates applied to high elevation rockfalls studies in the Western European Alps

Theoretical and Applied Climatology - Temperature is one of the most important aspects of mountain climates. The relationships between air temperature and rockfalls at high-elevation sites are very...     

The sensitivity of the Late Saalian (140?ka) and LGM (21?ka) Eurasian ice sheets to sea surface conditions

This work focuses on the Late Saalian (140?ka) Eurasian ice sheets?? surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). An Atmospheric General Circulation Model (AGCM), forced with two preexisting Last Glacial Maximum (LGM, 21?ka) SST reconstructions, is used to compute climate at 140 and 21?ka (reference glaciation). Contrary to the LGM, the ablation almost stopped at 140?ka due to the climatic cooling effect from the large ice sheet topography. Late Saalian SST are simulated using an AGCM coupled with a mixed layer ocean. Compared to the LGM, these 140?ka SST show an inter-hemispheric asymmetry caused by the larger ice-albedo feedback, cooling climate. The resulting Late Saalian ice sheet SMB is smaller due to the extensive simulated sea ice reducing the precipitation. In conclusion, SST are important for the stability and growth of the Late Saalian Eurasian ice sheet.     

The evolution of temperature extremes in the Gaspé Peninsula,Quebec, Canada (1974–2013)

The majority of natural hazards that affect Canadian territory are the result of extreme climate and weather conditions. Among these weather hazards, some can be calculated from the application of thresholds for minimum and maximum temperatures at a daily or monthly timescale. These thermal indices allowed the prediction of extreme conditions that may have an impact on the human population by affecting, for example, health, agriculture, and water resources. In this article, we discuss the methods used (RHtestsV4, SPLIDHOM, ClimPACT) then describe the steps followed to calculate the indices, including how we dealt with the problem of missing data and the necessity to identify a common methodology to analyze the time series. We also present possible solutions for ensuring the quality of meteorological data. We then present an overview of the results, namely the main trends and variability of extreme temperature for seven stations located in the Gaspé Peninsula from 1974 to 2013. Our results indicate some break points in time series and positive trends for most indices related to the rise of the temperatures but indicate a negative trend for the indices related to low temperatures for most stations during the study period.     

Formation and stability of schwertmannite in acidic mining lakes

Schwertmannite (ideal formula: Fe₈O₈(OH)₆SO₄) is typically found as a secondary iron mineral in pyrite oxidizing environments. In this study, geochemical constraints upon its formation are established and its role in the geochemical cycling of iron between reducing and oxidizing conditions are discussed. The composition of surface waters was analyzed and sediments characterized by X-ray diffraction, FTIR spectroscopy and determination of the Fe:S ratio in the oxalate extractable fraction from 18 acidic mining lakes. The lakes are exposed to a permanent supply of pyritegenous ferrous iron from adjacent ground water. In 3 of the lakes the suspended matter was fractionated using ultra filtration and analyzed with respect to their mineral composition. In addition, stability experiments with synthetic schwertmannite were performed. The examined lake surface waters were O₂-saturated and have sulfate concentrations (10.3 ± 5.5 mM) and pH values (3.0 ± 0.6) that are characteristic for the stability window of schwertmannite. Geochemical modeling implied that i) the waters were saturated with respect to schwertmannite, which controlled the activity of Fe³⁺ and sulfate, and ii) a redox equilibrium exists between Fe²⁺ and schwertmannite. In the uppermost sediment layers (1 to 5 cm depth), schwertmannite was detectable in 16 lakes—in 5 of them by all three methods. FTIR spectroscopy also proved its occurrence in the colloidal fraction (1-10 kDa) in all of the 3 investigated lake surface waters. The stability of synthetic schwertmannite was examined as a function of pH (2-7) by a 1-yr experiment. The transformation rate into goethite increased with increasing pH. Our study suggests that schwertmannite is the first mineral formed after oxidation and hydrolysis of a slightly acidic (pH 5-6), Fe(II)-SO₄ solution, a process that directly affects the pH of the receiving water. Its occurrence is transient and restricted to environments, such as acidic mining lakes, where the coordination chemistry of Fe³⁺ is controlled by the competition between sulfate and hydroxy ions (i.e. mildly acidic).     

Another Record: Ocean Warming Continues through 2021 despite La Ni?a Conditions

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (O...