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.     

A local-magnitude scale for Mt. Vesuvius from synthetic Wood-Anderson seismograms

The Local-Magnitude scale actually in use at Vesuvius Observatory is basedon the measure of seismogram coda duration, and calibrated with data fromIrpinia aftershocks. A recent study on local seismic attenuation at Mt.Vesuvius reveals coda shapes highly different from those from Irpiniaaftershocks, and a very low quality factor, if compared to the average Qof the region, indicating the necessity of the revision of the Magnitudescale, in order to better compare the seismic energy associated to the localseismicity of Mt. Vesuvius to that of other active volcanoes. Being theseismic attenuation parameters known in the area, we could correct theseismic amplitudes for the path effect to obtain precise estimates of theamplitude level of the displacement spectrum. Hence we estimated theMoment-Magnitude, M _W, for a set of well recorded micro-earthquakes.To use the Richter formulaM _L =log₁₀ A _max –log A₀(R)we estimated the log Amplitude-Distance correction curve, - log A₀(R),numerically synthesizing an S-wave-packet and letting it propagate in aearth medium with the same attenuation properties of those measured at Mt.Vesuvius. Then we synthesized the Wood-Anderson equivalent seismogram forthe same data set and used the distance correction in order to calculate theWood-Anderson Magnitude.This Magnitude scale was normalized in order to fit the Richter formulavalid for Southern California at a distance of 10 km, and resultsto be M _WA =log A + 1.34log(R) –1.10. The comparison of the Wood-Anderson scale with the Duration-Magnitude scalein routine use at Vesuvius Observatory indicates that care must be takenwhen the estimate of the Duration-Magnitude is carried out for smallearthquakes recorded at a site characterized by a high level of seismicnoise.     

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).     

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...     

Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...     

Spatial and temporal structure of Tropical Pacific interannual variability in 20th century coupled simulations

Tropical Pacific interannual variability is examined in nine state-of-the-art coupled climate models, and compared with observations and ocean analyses data sets, the primary focus being on the spatial structure and spectral characteristics of El Niño-Southern Oscillation (ENSO). The spatial patterns of interannual sea surface temperature (SST) anomalies from the coupled models are characterized by maximum variations displaced from the coast of South America, and generally extending too far west with respect to observations. Thermocline variability is characterized by dominant modes that are qualitatively similar in all the models, and consistent with the “recharge oscillator” paradigm for ENSO. The meridional scale of the thermocline depth anomalies is generally narrower than observed, a result that can be related to the pattern of zonal wind stress perturbations in the central-western equatorial Pacific. The wind stress response to eastern equatorial Pacific SST anomalies in the models is narrower and displaced further west than observed. The meridional scale of the wind stress can affect the amount of warm water involved in the recharge/discharge of the equatorial thermocline, while the longitudinal location of the wind stress anomalies can influence the advection of the mean zonal temperature gradient by the anomalous zonal currents, a process that may favor the growth and longer duration of ENSO events when the wind stress perturbations are displaced eastwards. Thus, both discrepancies of the wind stress anomaly patterns in the coupled models with respect to observations (narrow meridional extent, and westward displacement along the equator) may be responsible for the ENSO timescale being shorter in the models than in observations. The examination of the leading advective processes in the SST tendency equation indicates that vertical advection of temperature anomalies tends to favor ENSO growth in all the CGCMs, but at a smaller rate than in observations. In some models it can also promote a phase transition. Longer periods tend to be associated with thermocline and advective feedbacks that are in phase with the SST anomalies, while advective tendencies that lead the SST anomalies by a quarter cycle favor ENSO transitions, thus leading to a shorter period.     

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.     

Multidecadal variability of summer temperature over Romania and its relation with Atlantic Multidecadal Oscillation

We investigate the multidecadal variability of summer temperature over Romania as measured at 14 meteorological stations with long-term observational records. The dominant pattern of summer temperature variability has a monopolar structure and shows pronounced multidecadal variations. A correlation analysis reveals that these multidecadal variations are related with multidecadal variations in the frequency of four daily atmospheric circulation patterns from the North Atlantic region. It is found that on multidecadal time scales, negative summer mean temperature (TT) anomalies are associated with positive sea level pressure (SLP) anomalies centered over the northern part of the Atlantic Ocean and Scandinavia and negative SLP anomalies centered over the northern part of Africa. It is speculated that a possible cause of multidecadal fluctuations in the frequency of these four patterns are the sea surface temperature (SST) anomalies associated to the Atlantic Multidecadal Oscillation (AMO). These results have implications for predicting the evolution of summer temperature over Romania on multidecadal time scales.     

Consistency and fidelity of Indonesian-throughflow total volume transport estimated by 14 ocean data assimilation products

Monthly averaged total volume transport of the Indonesian throughflow (ITF) estimated by 14 global ocean data assimilation (ODA) products that are decade to multi-decade long are compared among themselves and with observations from the INSTANT Program (2004–2006). The main goals of the comparisons are to examine the consistency and evaluate the skill of different ODA products in simulating ITF transport. The ensemble averaged, time-mean value of ODA estimates is 13.6 Sv (1 Sv = 10⁶ m³/s) for the common 1993–2001 period and 13.9 Sv for the 2004–2006 INSTANT Program period. These values are close to the 15-Sv estimate derived from INSTANT observations. All but one ODA time-mean estimate fall within the range of uncertainty of the INSTANT estimate. In terms of temporal variability, the scatter among different ODA estimates averaged over time is 1.7 Sv, which is substantially smaller than the magnitude of the temporal variability simulated by the ODA systems. Therefore, the overall “signal-to-noise” ratio for the ensemble estimates is larger than one. The best consistency among the products occurs on seasonal-to-interannual time scales, with generally stronger (weaker) ITF during boreal summer (winter) and during La Nina (El Nino) events. The scatter among different products for seasonal-to-interannual time scales is approximately 1 Sv. Despite the good consistency, systematic difference is found between most ODA products and the INSTANT observations. All but the highest-resolution (18 km) ODA product show a dominant annual cycle while the INSTANT estimate and the 18-km product exhibit a strong semi-annual signal. The coarse resolution is an important factor that limits the level of agreement between ODA and INSTANT estimates. Decadal signals with periods of 10–15 years are seen. The most conspicuous and consistent decadal change is a relatively sharp increase in ITF transport during 1993–2000 associated with the strengthening tropical Pacific trade wind. Most products do not show a weakening ITF after the mid-1970s’ associated with the weakened Pacific trade wind. The scatter of ODA estimates is smaller after than before 1980, reflecting the impact of the enhanced observations after the 1980s. To assess the representativeness of using the average over a three-year period (e.g., the span of the INSTANT Program) to describe longer-term mean, we investigate the temporal variations of the three-year low-pass ODA estimates. The average variation is about 3.6 Sv, which is largely due to the increase of ITF transport from 1993 to 2000. However, the three-year average during the 2004–2006 INSTANT Program period is within 0.5 Sv of the long-term mean for the past few decades.     

Technical paper: FluMo—a mobile fluid–chemical monitoring unit for geothermal plants

A versatile fluid–chemical monitoring unit has been developed in the framework of the geothermal research platform Groß Schönebeck, Germany. It enables selective online and in situ measurements of various physico-chemical parameters at different surface locations of a geothermal fluid loop. Sensors are provided for pressure, temperature, volumetric flow rate, density, pH-value, redox potential, oxygen content, and electrical conductivity. In addition, the apparatus features two fluid samplers to manually collect fluid under in situ conditions and ultimately analyze the solution composition. All devices are mounted on a rack allowing easy transfer of the apparatus to other geothermal plants. The maximum operating pressure and temperature of the unit are 15 bar and 150 °C, respectively. The scientific and technical purpose of the system is to monitor a compositional variability of the produced fluid and chemical processes potentially occurring within the plant. These may result from reactions between the fluid and the surrounding materials, e.g., corrosion. Also, mineral precipitation as a consequence of temperature and/or pressure decrease or oxygen contamination may occur. This information is of paramount importance as so induced reactions might lead to failure of plant components or may damage the geothermal reservoir upon fluid reinjection and thus decrease injectivity.