Review on Morphological Insights of Self-Potential Anomalies on Volcanoes

Energy and thermal transfers in active volcanoes can play an important role incontrolling their dynamics depending on the hydrothermal state. Much geothermalenergy is released through the groundwater circulation, hot gas emission and thermalconduction. Therefore, it is very important to know the hydrological and thermalenvironments associated with volcanoes from the volcano-energetic point of view.However, it is difficult to evaluate these because of the availability of only a fewborehole data on the summit of volcanoes. Recent studies reveal that self-potential(SP) anomalies (up to some hundreds of mV) are observed on volcanoes, activefissure zones and/or fumarolic areas, suggesting that the SP anomalies are closelyrelated to heat-triggered phenomena such as thermoelectric and electrokinetic effectsdue to hydrothermal circulations. Therefore, SP studies can be appropriate for sensingthe thermal and hydrothermal states of volcanoes. In addition, monitoring SP anomaliescan be an efficient method for describing the change of thermal state and the evolutionof the hydrothermal (and volcanic) activities.In this paper, we have reviewed the origin of the SP anomalies associated withvolcanic phenomena theoretically as well as experimentally. Subsequently, wehave presented the results of many case studies and have classified the types ofanomalies in accordance with possible mechanisms. We have also described theresults of time variations of SP anomalies associated with volcanic activities. Timevarying SP fields exhibit the dynamic aspects of volcanic activities correspondingto the evolution of hydrothermal activity, changes in ground water circulation andmagma displacement. These morphological insights should lead to a quantitativeinterpretation of SP anomalies in volcanic regions.     

Datation par la méthode U/Th d'un travertin quaternaire du Sud-Est marocain : implications paléoclimatiques pendant le Pléistocène moyen et supérieur

A large travertine outcrop south of Errachidia, southern Morocco, was studied and U/Th dated. The carbonate fraction was provided by groundwaters then, as now, from the eastern High Atlas percolating through the regional Infra-Cenomanian aquifer. There were two main periods of accumulation at ca 262 kyr BP and 20–11.5 kyr BP separated by a long discontinuity with some limited weathering and erosion and correlated in part with a period of erosion at 30–20 kyr BP further to the west. The two travertine-deposition periods suggest increased rainfall and/or cooler thermal conditions in the eastern High Atlas source regions. Massive travertine accumulation ceased at the end of the Upper Pleistocene. To cite this article: L. Boudad et al., C. R. Geoscience 335 (2003).To cite this article: L. Boudad et al., C. R. Geoscience 335 (2003).     

Scientific achievements from the first phase (1997–2003) of the Global Geodynamics Project using a worldwide network of superconducting gravimeters

This paper aims to review the main scientific achievements which were obtained in the first phase (1997–2003) of the Global Geodynamics Project (GGP) consisting of a worldwide network of superconducting gravimeters (SG) of about 20 instruments. We show that the low noise levels reached by these instruments in various frequency bands allow us either to investigate new signals of very small amplitude or to better determine other signals previously seen. We first report new results in the long-period seismic band with special emphasis on the detection of the ₂S₁ normal mode and the splitting of the fundamental spheroidal mode ₂S₀ after the magnitude 8.4 Peru earthquake in 2001. We also discuss briefly the ‘hum’, which consists of a sequence of fundamental normal modes existing between 2 and 7 mHz even in the lack of any seismic excitation, and was first discovered on the Syowa (in Antarctica) instrument in 1998. We will comment on the search for the Slichter mode ₁S₁ of degree 1 which is associated with a translational motion of the inner core inside the liquid core. Atmospheric effects are reviewed from the local to the global scale and the improvement due to pressure loading computations on residual gravity signals is shown. An interesting study exhibiting the gravity consequence due to sudden rainfall and vertical mass motion in the atmosphere (without ground pressure change) is presented. The precision of the SGs leads to some convincing results in the tidal domain, concerning the fluid core resonance effect (free core nutation (FCN)) on diurnal tides or various loading effects (linear, non-linear) from the oceans. In particular, SGs gravity measurements are shown to be useful validating tools for ocean tides, especially if they are small and/or confined to coastal regions. The low instrumental drift of the SGs also permits to investigate non-tidal effects in time-varying gravity, especially of annual periodicity. Hydrology has also a signature which can be seen in SG measurements as shown by several recent studies. At even lower frequency, there is the Chandler motion of 435-day period which leads to observable gravity changes at the Earth's surface. We finally report on the progress done in the last years in the problem of calibrating/validating space satellite data with SG surface gravity measurements.     

Fluid inclusions in charnockites from the Bjerkreim-Sokndal massif (Rogaland,southwestern Norway): fluid origin and in situ evolution

Fluid inclusions and mineral associations were studied in late-stage charnockitic granites from the Bjerkreim-Sokndal lopolith (Rogaland anorthosite province). Because the magmatic and tectonic evolutions of this complex appear to be relatively simple, these rocks are a suitable case for investigation of the origin and evolution of granulitic fluids. Fluid inclusions, primarily contained in quartz, can be divided into four types: carbonic (type I), N₂-bearing (type II), CO₂+H₂O (type III) and aqueous inclusions (type IV). For each type, the role of leakage and fluid mixing are discussed from microthermometric and Raman spectrometric data. The most striking features of CO₂-rich inclusions (the predominant fluid) is the presence of graphite in numerous, trail-bound inclusions (Ib) and its absence in a few isolated, very dense (d=1.16), pure CO₂ inclusions (Ia) and in the late carbonic inclusions (Ic). Fluid chronology and mineral assemblages suggest that carbonic Ia inclusions represent the first fluid (pure CO₂) trapped at or close to magmatic conditions (T=780–830° C, fO₂=10^-15 atm and P=7.4±1 kb), outside the graphite stability field. In contrast, type Ib inclusions enclosed graphite particles from a channelized fluid during retrograde rock evolution (P=3–4 kb and T=600° C). Decreases in T-fO₂ could explain a progressive evolution from a CO₂-rich fluid to an H₂O-rich fluid in a closed C–O–H system. However, graphite destabilization observed in type Ic inclusions implies some late introduction of external water during the last stage of retrogression. The main results of this study are the following: (1) a carbonic fluid was present in an early stage of rock evolution (probably in the charnockitic magma) and (2) this granulite occurrence offers good evidence of crossing the graphite stability field during post-magmatic evolution.     

Instrumental factors affecting the fringe contrast in optical interferometers

Interference fringes are the prime observable quantity in astronomical optical and radio interferometers. To maximize the signal-to-noise ratio it is important to keep instrumental causes of fringe contrast decrease to a minimum. I discuss these and derive the tolerances to be, placed on them.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

M m: Extension to Love waves of the concept of a variable-period mantle magnitude

We extend to Love waves the concept of the mantle magnitudeM _mintroduced recently for Rayleigh waves. Spectral amplitudesX() of Love waves in the 50–300 s period range are measured on broad-band records from major events. A distance correctionC _D, regionalized to reflect the influence of different tectonic paths, and a source correctionC _S, compensating for the variation of excitation with period are effected; the exact geometry and depth of the event are however ignored. The resulting expression

Thermodynamics of open networks: Ordering and entropy in NaAlSiO4 glass,liquid, and polymorphs

The thermodynamic properties of carnegieite and NaAlSiO₄ glass and liquid have been investigated through C _p determinations from 10 to 1800 K and solution-calorimetry measurements. The relative entropies S ₂₉₈-S₀ of carnegieite and NaAlSiO₄ glass are 118.7 and 124.8 J/mol K, respectively. The low-high carnegieite transition has been observed at 966 K with an enthalpy of transition of 8.1±0.3 kJ/mol, and the enthalpy of fusion of carnegieite at the congruent melting point of 1799 K is 21.7±3 kJ/mol. These results are consistent with the reported temperature of the nepheline-carnegieite transition and available thermodynamic data for nepheline. The entropy of quenched NaAlSiO₄ glass at 0 K is 9.7±2 J/mol K and indicates considerable ordering among AlO₄ and SiO₄ tetrahedra. In the liquid state, progressive, temperature-induced Si, Al disordering could account for the high configurational heat capacity. Finally, the differences between the entropies and heat capacities of nepheline and carnegieite do not seem to conform to current polyhedral modeling of these properties     

Les bilans énergétiques en météorologie dynamique

Résumé L'objet de cet article est d'établir les bilans énergétiques dans un référentiel quelconque, animé d'un mouvement variable d'un point à un autre et d'un instant à un autre. Le bilan de l'énergie mécanique se déduit, grâce au théorème des forces vives, des équations du mouvement de l'air par rapport au référentiel mobile. Le bilan qui exprime la conservation de l'énergie totale s'obtient en transposant, dans le référentiel mobile, l'expression du premier principe de la thermodynamique, énoncé dans le référentiel galiléen.

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Summary In this paper, energy equations of balance are established in any type of frame moving with an arbitrary, variable velocity with respect to space aud time. The equation of balance of mechanical energy can be deduced from the eqnations of motion of the air with respect to the moving frame. The equation of balance showing the conservation of total energy will be obtained by transposing in the moving frame, the expression of the first principle of thermodynamics given for the absolute frame.