Spatial vent opening probability map of Etna volcano (Sicily, Italy)

We produce a spatial probability map of vent opening (susceptibility map) at Etna, using a statistical analysis of structural features of flank eruptions of the last 2?ky. We exploit a detailed knowledge of the volcano structures, including the modalities of shallow magma transfer deriving from dike and dike-fed fissure eruptions analysis on historical eruptions. Assuming the location of future vents will have the same causal factors as the past eruptions, we converted the geological and structural data in distinct and weighted probability density functions, which were included in a non-homogeneous Poisson process to obtain the susceptibility map. The highest probability of new eruptive vents opening falls within a N-S aligned area passing through the Summit Craters down to about 2,000?m?a.s.l. on the southern flank. Other zones of high probability follow the North-East, East-North-East, West, and South Rifts, the latter reaching low altitudes (～400?m). Less susceptible areas are found around the faults cutting the upper portions of Etna, including the western portion of the Pernicana fault and the northern extent of the Ragalna fault. This structural-based susceptibility map is a crucial step in forecasting lava flow hazards at Etna, providing a support tool for decision makers.     

The ‘humped’ soil production function: eroding Arnhem Land,Australia

We report erosion rates and processes, determined from in situ‐produced beryllium‐10 (¹⁰Be) and aluminum‐26 (²⁶Al), across a soil‐mantled landscape of Arnhem Land, northern Australia. Soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness. These results thus quantify a well‐defined ‘humped’ soil‐production function, in contrast to functions reported for other landscapes. We compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the Bega Valley, south‐eastern Australia, and found remarkable similarities in rates. The critical difference in this work was that the Arnhem Land landscapes were either bedrock or mantled with soils greater than about 35 cm deep, with peak soil production rates of about 20 m/Ma under 35–40 cm of soil, thus supporting previous theory and modeling results for a humped soil production function. We also show how coupling point‐specific with catchment‐averaged erosion rate measurements lead to a better understanding of landscape denudation. Specifically, we report a nested sampling scheme where we quantify average erosion rates from the first‐order, upland catchments to the main, sixth‐order channel of Tin Camp Creek. The low (～5 m/Ma) rates from the main channel sediments reflect contributions from the slowly eroding stony highlands, while the channels draining our study area reflect local soil production rates (～10 m/Ma off the rocky ridge; ～20 m/Ma from the soil mantled regions). Quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the Earth's soil resource under different erosional regimes. Copyright © 2009 John Wiley & Sons, Ltd.     

High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater

The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.     

A method for determination of epicenters of near earthquakes

Summary A method is developed, which permits a rapid and reliable determination of the location of near epicenters (within about 10^o) using the differences of arrival times of a common phase (usually Sg) to a net of three stations. The resulting equation for computation of epicentral distances is solved numerically once for all by an electronic computer for every station triangle and for all possible time differences for every wave used. The calculated epicentral distances and coordinates are arranged in tables with the two travel-time differences for each triangle as entries. Such tables permit an immediate solution of the problem in every special case. The accuracy of the method is investigated, and necessary precautions in its use are emphasized. Application is made to a few cases of Sg recorded at the Swedish stations.

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Zusammenfassung Eine Methode wird entwickelt, die eine schnelle und zuverlässige Bestimmung der Lage von nahegelegenen Epizentren (innerhalb rund 10^o) mittels der Laufzeitdifferenzen einer gegebenen Welle (gewöhnlichSg) in einem Netz von drei Stationen ermöglicht. Die erhaltene Gleichung für die Berechnung der Herdentfernungen wird mittels einer elektronischen Rechenmaschine für jedes Stations-dreieck und für alle möglichen Zeitdifferenzen für jede verwendete Welle ein für allemal numerisch gelöst. Die berechneten Herdentfernungen und-Koordinaten werden in Tabellenform dargestellt mit den beiden Laufzeitdifferenzen für jedes Dreieck als Eingangswerte. Solche Tabellen ermöglichen eine unmittelbare Lösung des Problems in jedem einzelnen Fall. Die Genauigkeit der Methode wird untersucht, und die notwendigen Vorsichtsmassregeln bei ihrer Verwendung werden hervorgehoben. Die Methode wird auf einige Registrierungen vonSg an den schwedischen Stationen angewendet.

     

GPS network monitors the Western Alps' deformation over a five-year period: 1993–1998

  The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and 2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation. Received: 27 November 2000 / Accepted: 17 September 2001     

The Role of Pressure in Producing Compositional Diversity in Intraplate Basaltic Magmas

Basaltic magmas found in intraplate suites appear to followmore than one differentiation trend. Many ocean island suitesfollow the ocean island tholeiitic trend, with the basalts differentiatingfrom olivine tholeiite through basaltic andesite, andesite,and dacite to sodic rhyolite. Many continental intraplate magmaticregimes, such as those of the Snake River Plain and the plutonicsequences associated with massif anorthosites, follow the potassicsilica-saturated alkalic trend, in which basalt differentiatesfrom olivine tholeiite through ferrobasalt (jotunite or ferrodiorite),Fe-rich intermediate rocks (trachybasalt or monzonite), andtrachyte (syenite) to potassic rhyolites and granites. Crystallizationexperiments on an olivine tholeiite from the Snake River Plainshow that the basaltic portions of the ocean island tholeiitictrend and the potassic silica-saturated alkalic trend (whichleads to strong alkali, P, Ti, and Fe enrichment and silicadepletion) can arise from the same ‘dry’ tholeiiticparental magma. These compositional differences are inducedby changes in phase equilibria as a function of pressure, withthe ocean island tholeiitic series arising from crystal–liquiddifferentiation at low pressure and the potassic silica-saturatedalkalic series arising via differentiation at elevated pressures. KEY WORDS: tholeiite differentiation; experimental petrology; phase equilibria; ferrodiorite; ferrobasalt     

Nonlinear Coupled Motions for a Given Two-Point Tension Mooring System

—The nonlinear behaviors of plane coupled motions for a given two-point tension mooring sys-tem,are discussed in the present paper.For a cylinder moored by two taut lines under the action ofgravity,buoyance and forces due to wave-current and mooring lines,a mathematical model of motionswith three degrees of freedom is established.The steady solution and stability are analyzed.By integratingthe equations of motions,history,phase map and Poincare map are obtained.The Liapunov exponentsare also computed.The numerical results show that:the horizontal movement will increase,and stabilitywill also increase as the steady force increases.The amplitude of responses will decrease as time-dependentforces decrease.Because of the geometric nonlinearity,there exist many windows bifurcating to pseudo-pe-riodic or multi-periodic solution.The bifurcating patterns may be different.The behaviors are very com-plex.Under wave excitation alone,the motions are nonsymmetrical but still symmetrical statistically.     

Evaluation of toxicity in tributaries of the Mersey estuary using the isopod Asellus aquaticus (L.)

Increasing numbers of industrial, agricultural and natural chemicals are present in sewage effluent and are known to elicit toxic effects in laboratory exposures, but little is known of their combined sub-lethal effect in the field. In this study, a combination of esterase activity and ventilation rate assays was performed to determine the neurological and physiological function of the freshwater crustacean Asellus aquaticus (L.) at sites above and below a sewage treatment works (STW). Cholinesterase and carboxylesterase activities were significantly inhibited (n=8, P<0.05) and ventilation rates increased (n=8, P=0.0001) in A. aquaticus at STW sites compared to those from reference sites, indicating a decrease in neurological and physiological function. The ecological relevance of these findings for the population dynamics of the organisms in the field is discussed.     

Heat,volume and chemical fluxes from submarine venting: A synthesis of results from the Rainbow hydrothermal field, 36°N MAR

High-temperature hydrothermal activity occurs in all ocean basins and along ridge crests of all spreading rates. While it has long been recognized that the fluxes associated with such venting are large, precise quantification of their impact on ocean biogeochemistry has proved elusive. Here, we report a comprehensive study of heat, fluid and chemical fluxes from a single submarine hydrothermal field. To achieve this, we have exploited the integrating nature of the non-buoyant plume dispersing above the Rainbow hydrothermal field, a long-lived and tectonically hosted high-temperature vent site on the Mid-Atlantic Ridge. Our calculations yield heat and volume fluxes for high-temperature fluids exiting the seafloor of ～0.5 GW and 450 L s^?1, together with accompanying chemical fluxes, for Fe, Mn and CH₄ of ～10, ～1 and ～1 mol s^?1, respectively. Accompanying fluxes for 25 additional chemical species that are associated with Fe-rich plume particles have also been calculated as they are transported away from the Rainbow vent site before settling to the seabed. High-temperature venting has been found to recur at least once every ～100 km along all slow-spreading ridges investigated to-date, with half of all known sites on the Mid-Atlantic Ridge occurring as long-lived and tectonically hosted systems. If these patterns persist along all slow- and ultraslow-spreading ridges, high-temperature venting of the kind reported here could account for ～50% of the on-axis hydrothermal heat flux along ～30,000 km of the ～55,000 km global ridge crest.     

New aromatic biomarkers and possible maturity indicators found in New Albany Shale extracts

Aromatic hydrocarbons from benzene extracts of New Albany Shale were characterized. A biomarker that has a molecular weight of 546 and a structural configuration consistent with that of an alkyl-aromatic hydrocarbon (C₄₀H₆₆) was tentatively identified. It was found that the relative concentrations of the biomarker are indicative of differing levels of thermal maturity of the shale organic matter. A 40-carbon bicyclic carotenoid (C₄₀H₄₈) is proposed as the geochemical precursor of this biomarker. Thermal maturity of the shale organic matter can also be differentiated by observing differences in “fingerprints” as obtained by field-ionization mass spectrometry on the aromatic hydrocarbon fraction. Using this technique, we found that the more mature shale samples from southeastern Illinois contain more low molecular weight extractable aromatic hydrocarbons and the less mature shale samples from northwestern Illinois contain more high molecular weight extractable aromatic hydrocarbons. It was demonstrated that field-ionization and tandem mass spectrometric techniques through fingerprint and individual compound identification, are useful for shale aromatic hydrocarbon fraction characterization and for thermal maturation interpretation.