The role of the Pernicana Fault System in the spreading of Mt. Etna (Italy) during the 2002–2003 eruption     

Marco?NeriEmail author  Valerio?Acocella  Boris?Behncke 《Bulletin of Volcanology》2004,66(5):417-430

Flank instability and collapse are observed at many volcanoes. Among these, Mt. Etna is characterized by the spreading of its eastern and southern flanks. The eastern spreading area is bordered to the north by the E–W-trending Pernicana Fault System (PFS). During the 2002–2003 Etna eruption, ground fracturing along the PFS migrated eastward from the NE Rift, to as far as the 18 km distant coastline. The deformation consisted of dextral en-echelon segments, with sinistral and normal kinematics. Both of these components of displacement were one order of magnitude larger (~1 m) in the western, previously known, portion of the PFS with respect to the newly surveyed (~9 km long) eastern section (~0.1 m). This eastern section is located along a pre-existing, but previously unknown, fault, where displaced man-made structures give overall slip rates (1–1.9 cm/year), only slightly lower than those calculated for the western portion (1.4–2.3 cm/year). After an initial rapid motion during the first days of the 2002–2003 eruption, movement of the western portion of the PFS decreased dramatically, while parts of the eastern portion continued to move. These data suggest a model of spreading of the eastern flank of Etna along the PFS, characterized by eruptions along the NE Rift, instantaneous, short-lived, meter-scale displacements along the western PFS and more long-lived centimeter-scale displacements along the eastern PFS. The surface deformation then migrated southwards, reactivating, one after the other, the NNW–SSE-trending Timpe and Trecastagni faults, with displacements of ~0.1 and ~0.04 m, respectively. These structures, along with the PFS, mark the boundaries of two adjacent blocks, moving at different times and rates. The new extent of the PFS and previous activity over its full length indicate that the sliding eastern flank extends well below the Ionian Sea. The clustering of seismic activity above 4 km b.s.l. during the eruption suggests a deep décollement for the moving mass. The collected data thus suggests a significant movement (volume >1,100 km³) of the eastern flank of Etna, both on-shore and off-shore.Editorial responsibility: R. Cioni  相似文献   

Experimental study of the stability of aluminate-borate complexes in hydrothermal solutions     

Boris Tagirov  Jacques Schott  Jocelyne Escalier 《Geochimica et cosmochimica acta》2004,68(6):1333-1345

Formation of aqueous aluminate-borate complexes was characterized at 25°C using ²⁷Al NMR spectroscopy, and at 50-200°C via measurements of gibbsite and boehmite solubility in the presence of boric acid. ²⁷Al spectra performed at pH = 9 in Al-B solution with m(B) = 0.02 show the presence of two peaks at 80.5 and 74.5 ppm which correspond to Al(OH)₄⁻ and a single Al-substituted Q¹_Al dimer, Al(OH)₃OB(OH)₂⁻, respectively. In 0.08 m and 0.2 m borate solution, a third peak appears at 68.5 ppm which can be assigned to the Q²_Al trimer Al(OH)₂O₂(B(OH)₂)₂⁻. These chemical shifts are close to those measured for Al(OH)₃OSi(OH)₃⁻ and Al(OH)₂O₂(Si(OH)₃)₂⁻ (74 and 69.5 ppm, respectively; Pokrovski et al., Min. Mag.62a (1998), 1194) which demonstrates the similar structure of Al-B and Al-Si complexes formed in alkaline solutions. Gibbsite and boehmite solubility were measured in weakly basic solutions as a function of boric acid concentration at 50°C and 78 to 200°C, respectively. Equilibrium was reached within several days at m(B) = 0.01-0.1, but more slowly at higher boron concentrations, and at 50°C and m(B) = 0.2, Al concentration increased continuously during at least 3 months as a result of the sluggish formation of Al-polyborates. The equilibrium constant of the reaction Al(OH)₄⁻ + B(OH)₃⁰_(aq) = Al(OH)₃OB(OH)₂⁻ + H₂O decreases very slowly with increasing temperature to 200°C. The log K values are 1.58 ± 0.10, 1.46 ± 0.10, 1.52 ± 0.15, and 1.25 ± 0.15 at 50, 78, 150 and 200°C, respectively, which result in the following values of the standard thermodynamic properties for this reaction: Δ_rG⁰ = −9.22 ± 3.25 kJ/mol, Δ_rH⁰ = −4.6 ± 2.5 kJ/mol, Δ_rS⁰ = 15.5 ± 6.9 J/mol K. The thermodynamic data generated in this study indicate that Al-B complexes can dominate aqueous aluminum speciation in solutions containing ≥0.7 g/L of boron at temperature to at least 400°C.  相似文献   

Rôle des héritages latéritiques et du niveau des nappes dans l'évolution des modelés et des sols en zone intertropicale forestière humide     

Dieudonné Bitom  Boris Volkoff  Anicet Beauvais  Frédérique Seyler  Paul-Désiré Ndjigui 《Comptes Rendus Geoscience》2004,336(13):1161-1170

Analysis of landscapes and soil covers from the outer to the inner part of a $75\text{km}\times 60\text{km}$ watershed in the South-Cameroon rainforest zone, characterized by important remnants of inherited ferricretes and stable hydrostatic base levels, indicates that the development of present landforms has not involved significant erosion by slope retreat because of the relative preservation of downslope residual ferricrete and that soil covers have vertically decayed under in situ geochemical process. To cite this article: D. Bitom et al., C. R. Geoscience 336 (2004).  相似文献   

Halite solubility in dead sea waters     

Boris S. Krumgalz 《Marine Chemistry》1989,27(3-4)

The solubilities of halite in Dead Sea waters and in their mixtures with Mediterranean Sea waters were estimated using Pitzer's equations. The calculated halite saturation for Dead Sea waters sampled at various occasions during 1979–1983 is in good agreement with the naturally observed phenomenon of halite deposition at this time. A halite saturation curve for mixtures of Dead Sea and Mediterranean Sea waters has been obtained and permits the prediction of halite deposition in these mixtures on evaporation.  相似文献   

Natural and anthropogenic forcing of Holocene lake ecosystem development at Lake Uddelermeer (The Netherlands)     

Stefan Engels  Rogier van Oostrom  Chiara Cherli  Jennifer A. J. Dungait  Boris Jansen  J. M. van Aken  Bas van Geel  Petra M. Visser 《Journal of Paleolimnology》2018,59(3):329-347

Lake Uddelermeer (The Netherlands) is characterized by turbid conditions and annual blooms of toxic cyanobacteria, which are supposed to be the result of increased agricultural activity in the twentieth century AD. We applied a combination of classic palaeoecological proxies and novel geochemical proxies to the Holocene sediment record of Lake Uddelermeer (The Netherlands) in order to reconstruct the natural variability of the lake ecosystem and to identify the drivers of the change to the turbid conditions that currently characterize this lake. We show that the lake ecosystem was characterized by a mix of aquatic macrophytes and abundant phytoplankton between 11,500 and 6000 cal year BP. A transition to a lake ecosystem with clear-water conditions and relatively high abundances of ‘isoetids’ coincides with the first signs of human impact on the landscape around Lake Uddelermeer during the Early Neolithic (ca. 6000 cal year BP). An abrupt and dramatic ecosystem shift can be seen at ca. 1030 cal year BP when increases in the abundance of algal microfossils and concentrations of sedimentary pigments indicate a transition to a turbid phytoplankton-dominated state. Finally, a strong increase in concentrations of plant and faecal biomarkers is observed around 1950 AD. Canonical Correspondence Analysis suggests that reconstructed lake ecosystem changes are best explained by environmental drivers that show long-term gradual changes (sediment age, water depth). These combined results document the long-term anthropogenic impact on the ecosystem of Lake Uddelermeer and provide evidence for pre-Industrial Era signs of eutrophication.  相似文献   

Bounding the integer bootstrapped GNSS baseline’s tail probability in the presence of stochastic uncertainty   总被引：1，自引：0，他引：1  

Steven E. Langel  Samer M. Khanafseh  Boris Pervan 《Journal of Geodesy》2016,90(11):1293-1305

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Erratum to: A geomorphological seabed classification for the Weddell Sea,Antarctica     

Kerstin Jerosch  Gerhard Kuhn  Ingo Krajnik  Frauke Katharina Scharf  Boris Dorschel 《Marine Geophysical Researches》2016,37(2):143-143

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D. Rouwet,B. Christenson,F. Tassi,J. Vandemeulebrouck (eds): Volcanic Lakes     

Boris Chako Tchamabé 《Bulletin of Volcanology》2015,77(9):1-4

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Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea,Antarctica     

Boris Cisewski  Volker H. Strass  Monika Rhein  Sören Krägefsky 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):78-94

Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64°S, 66.5°S and 69°S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day–night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and –15 mm s^?1. However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (<50 m) at 66.5°S. This period coincided with the decay of sea ice coverage at 64°S and 66.5°S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67°S to 65°S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding.  相似文献   

Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?     

Walter Finsinger  Daniele Colombaroli  Jacques‐Louis De Beaulieu  Verushka Valsecchi  Boris Vannière  Elisa Vescovi  Emmanuel Chapron  André F. Lotter  Michel Magny  Willy Tinner 《第四纪科学杂志》2010,25(8):1239-1247

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献