The model of an eruptive column produced by phreatomagmatic explosions

This paper presents the results from the simulation of a phreatomagmatic eruption, in which the formation of the eruptive column is controlled by interaction between magma and water or ice. The process leads to intensive fragmentation of the magma and to mixing of ash and steam with ambient air. Such processes were typical of the initial phase in the April 2010 eruption of Eyjafjallajökull Volcano. It is hypothesized that phreatic explosions produce a dynamic pulsating system that consists of buoyant volumes of the mixture (thermals) that are forming at the base of the eruptive column. A 3-D simulation was used to assess two possible regimes in the evolution of the eruptive column: (1) continuous transport of the mixture into the eruptive column through its base for the case in which the thermals are generated at a high rate and (2) periodic flotation of the thermals whose diameters are comparable with that of the base of the eruptive column. It is shown that one can find a suitable selection of the initial concentrations of ash, steam, and air to achieve a satisfactory agreement between theory and actually observed heights of the gas–ash “clouds” that were formed during the Eyjafjallajökull eruption. The data for our calculations were taken from publications. We also investigated how wind and the changes in the initial parameters affect the process.     

MFCI experiments on the influence of NaCl-saturated water on phreatomagmatic explosions

Molten–Fuel–Coolant Interaction (MFCI) experiments were performed using remelted foiditic rock samples from the West Eifel volcanic field (Germany). Two experimental series were carried out with one magmatic melt and two water compositions. Bi-distilled water was used in the first series (DW-1 to DW-5). In the second series (SW-1 to SW-5), the bi-distilled water was saturated (350 g L^− 1) with sodium chloride (NaCl). For both experimental series the fragmentation history and the energy release were recorded and compared. The smallest particles (≤ 125 μm) were studied using scanning electron microscopy (SEM). Most MFCI experiments with bi-distilled water reached higher explosion intensities than the experiments with the saline water. This was accompanied by higher particle ejection velocities as well as the formation of more fine-grained and more interactive particles of angular shape. Additionally, the smallest artificial pyroclasts were examined by evolved gas analyses (EGA). The particles from the MFCI experiments with salt solutions are found to contain more sodium hydroxide (NaOH). These observations can be explained by thermodynamic arguments. In contrast to the MFCI experiments with pure water, an additional reaction occurs with saline water that results in evolution of hydrogen chloride (HCl) gas and leaves a residue of sodium hydroxide. The MFCI process with saline water consumes more enthalpy and Gibbs free energy, so that less energy is available for the explosion. With other sodium halides dissolved in the water (NaF, NaBr or NaI) the additional reaction can be predicted to have greater or lesser effects on phreatomagmatic explosions.     

Calculating the seismic energy of earthquakes and explosions

An analysis of the Zoeppritz-Wiechert and Golitsyn equations commonly used to calculate the energy of an earthquake showed that these equations are at variance with the physical assumptions made before deriving them. The value of seismic energy as found from the equations currently used for the purpose is overestimated by 1–2 orders of magnitude. It is suggested that the seismic energy of earthquakes can be found from its value over a half-period of the maximum swing.     

A new mathematical model of asymmetric hydraulic fracture growth

Hydraulic fractures generated by fluid injection in rock formations are often mapped by seismic monitoring. In many cases, the microseismicity is asymmetric relative to the injection well, which has been interpreted by stress gradient along the direction of the hydraulic fracture. We present a mathematical model of asymmetric hydrofracture growth based on relations between the solid‐phase stress and the fracture hydraulics. For single fracture and single injection point, the model has three parameters, hydraulic conductivities of the fracture wings, and normalised stress gradient and predicts the positions of the fracture tips as functions of time. The model is applied to a set of microseismic event locations that occurred during and after an injection process. Two different methods are suggested that make it possible to delineate the fracture tips from the set of microseismic events. This makes it possible to determine the model parameters and to check the agreement between the model prediction and the measured data. The comparison of the measured and modelled growth of fracture wings supports both the assumption of the non‐zero stress gradient and the existence of the post‐injection unilateral growth.     

Geoneutrinos and the energy budget of the Earth

The total energy loss of the Earth is well constrained by heat flux measurements on land, the plate cooling model for the oceans, and the buoyancy flux of hotspots. It amounts to 46 ± 2 TW. The main sources that balance the total energy loss are the radioactivity of the Earth's crust and mantle, the secular cooling of the Earth's mantle, and the energy loss from the core. Only the crustal radioactivity is well constrained. The uncertainty on each of the other components is larger than the uncertainty of the total heat loss. The mantle energy budget cannot be balanced by adding the best estimates of mantle radioactivity, secular cooling of the mantle, and heat flux from the core. Neutrino observatories in deep underground mines can detect antineutrinos emitted by the radioactivity of U and Th. Provided that the crustal contribution to the geoneutrino flux can be very precisely calculated, it will be possible to put robust constraints on mantle radioactivity and its contribution to the Earth's energy budget. Equally strong constraints could be obtained from a deep ocean observatory without the need of crustal correction. In the future, it may become possible to obtain directional information on the geoneutrino flux and to resolve radial variations in concentration of heat producing elements in the mantle.     

Torque balance and energy budget for the precessionally driven dynamo

The feasibility of a precessionally driven dynamo is investigated. The relative orientation of the angular-velocity vectors of the mantle and core and the precession vector of the earth are determined from a torque balance. The core and mantle are acted upon by separate gravitational torques and mutual interaction torques resulting from pressure, viscous and magnetic stresses at the core-mantle interface. The viscous and magnetic torques are determined using the results of a detailed analysis of the Ekman-Hartmann and magnetic diffusion layers generated at the core-mantle interface by the misalignment of the mantle and core angular-velocity vectors. The dissipative torques are found to be weaker by a factor of 10^?4 than those estimated by Malkus (1968) and Stacey (1973), resulting in only 3.5 · 10⁷ W being extracted from the rotational kinetic energy of the earth by these mechanisms. Furthermore, it is found that all of this energy is dissipated in the boundary layers at the core-mantle interface and none is available to drive the geodynamo.     

Root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar–diatreme volcanoes

The understanding of processes within the root zone of maar–diatreme volcanoes is important for the interpretation of the geology, volcanology and even hazard assessment of these volcanoes. In the phreatomagmatic model of pipe formation, the irregularly shaped root zone is the site of the phreatomagmatic explosions, and thus functions as the “engine” for pipe formation. In this model the root zone grows over a period of time in a series of many single thermohydraulic, i.e. phreatomagmatic, explosions. The explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels. The ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole-like fashion into the root zone. Many phreatomagmatic eruptions consequently result in the formation of a cone-shaped diatreme. Thus with ongoing eruptions the cone-shaped diatreme has to grow systematically both in depth and diameter. During its growth, processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone. At the surface, the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter.Thermohydraulic explosions, which fragment both magma and the surrounding country rocks, mostly occur within the bottom part of the root zone. Violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme. In larger pipes, via expansion of the mixture of highly pressurized water vapor, juvenile gas phases and explosively produced tephra, the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt. Diatreme-clearing events in large pipes are difficult or impossible to maintain, since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra. Knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes. The combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types.It is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar–diatreme and related volcanoes.     

核爆、化爆、地震识别研究综述

地震学方法是监测地下核试验最为重要的方法.为准确鉴别地下核试验,不仅包括识别核爆炸与天然地震,还包括对化学爆炸震源类型的识别.论文从核爆炸与天然地震的识别、化学爆炸与地震的识别、核爆炸与化学爆炸的识别三个方面对国内外的研究状况分别进行了综述,较为详尽地阐述了从统计分析和信号处理的角度进行研究的进展状况,并对目前的研究进展进行了分析总结,最后对未来的核爆监测识别研究的发展趋势进行了展望,提出了一些建议.     

Analytical model of explosions in a rarefied atmosphere

A new model of explosion products expansion in rarified gas is obtained. This model is based on an approach taking into account the energy dissipation in the ??snowplow?? model, thus making it possible to obtain an exact analytical solution and results which are in good agreement with experimental data. A comparison of the new model with the currently existing models (Simple Snowplow Model, Stuart??s model and Holway??s model) is indicative of the fact that the latter can be described in the framework of the new model. Alongside with that, the new model is able to take into account yet more processes not considered in the existing models. A comparison with the Spolokh-1 experiment demonstrates good agreement with data obtained in this experiment.     

非均匀灌溉棉田能量平衡特征研究

运用国际能量平衡实验(EBEX-2000)的湍流、净辐射和土壤观测资料,运用涡动相关法分析了非均匀灌溉引起的热内边界层发展条件下近地层感热、潜热通量特征,并对有无灌溉两种条件下的能量闭合度进行了对比分析.在计算感热、潜热通量过程中,分别将Schotanus订正和Webb订正纳入了考虑范围,研究了两种订正方法对计算湍流热通量的影响.研究结果发现,由于非均匀灌溉生成的热内边界层使得近地层感热通量受到抑制,潜热通量出现波动,该现象在8.7 m比2.7 m 更为显著.非均匀灌溉导致的热内边界层的存在使得近地层能量闭合度偏低,能量平衡比率约为0.65;而没有热内边界层存在时,近地层能量平衡比率约为0.70.本实验中,Schotanus订正使得感热通量显著减小,其订正量日平均值约为-8 W/m2,占净辐射的近4%;Webb订正量日平均值约为2 W/m2,对能量平衡的影响较小.     

A two-stage model of fracture of rocks

In this paper we propose a two-stage model of rock fracture. In the first stage, cracks or local regions of failure are uncorrelated and occur randomly throughout the rock in response to loading of pre-existing flaws. As damage accumulates in the rock, there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop. Based on statistical arguments, a critical density of damage will occur where clusters of flaws become large enough to lead to larger-scale failure of the rock (stage two). While crack interaction and cooperative failure is expected to occur within clusters of closely spaced cracks, the initial development of clusters is predicted based on the random variation in pre-existing flaw populations. Thus the onset of the unstable second stage in the model can be computed from the generation of random, uncorrelated damage. The proposed model incorporates notions of the kinetic (and therefore time-dependent) nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation. The advantage offered by this model is that its salient features are valid for fracture processes occurring over a wide range of scales including earthquake processes. A notion of the rank of fracture (fracture size) is introduced, and criteria are presented for both fracture nucleation and the transition of the failure process from one scale to another.     

Geothermal energy release at the Solfatara of Pozzuoli (Phlegraean Fields): Phreatic and phreatomagmatic explosion risk implications

The H₂O, CO₂ and H₂S outputs at the Solfatara of Pozzuoli have been measured and a map of the exhaling areas has also been made. The energy released at the surface by the fluids has been estimated to be 10¹⁹ ergs/day.The presence of aquifers at Phlegraean Fields increases the phreatic and phreatomagmatic explosion risk.Our results suggest that even if an uprising magma may interact with water at depth, an explosion could occur only at the shallow levels of a few hundred meters. Since the transfer of energy toward the surface is favoured by the presence of fractures, a detailed analysis of the deep fracture network would help to evaluate the risk levels of the various areas of Phlegraean Fields.     

A model of Meridional energy transport

Summary A number of relations describing various forms of energy transport in the atmosphere have been derived and several simplification, unsuitable according to the author's opinion, which are introduced in applying them, are pointed out.     

Budgeting for the budget

R esearch N otes
The prospect of advanced astrometric satellites raises the tantalizing possibility that we will be able to make astrometric measurements at such a precision as to place constraints on dark energy parameters. That is the premise outlined by Fiona Ding and Rupert Croft of Carnegie Mellon University, Pittsburgh, USA, in Monthly Notices of the Royal Astronomical Society ,     

A study of the kinetic energy budget of the troposphere over the Caribbean Sea and the Gulf of Mexico

Summary The budget of kinetic energy over the Caribbean Sea and the Gulf of Mexico during the winter (November–April) and Summer (May–October) half-years of 1960 is established for the finite atmospheric layers 1000/850, 850/700, 700/500, and 500/300 mb. Vertical transports, lateral outflow, and generation of kinetic energy are computed directly from twice-daily aerological soundings, while the dissipation term is obtained as a residual. The frictional dissipation in the boundary layer is independently computed from 1960 ship observations. Kinetic energy dissipation is of the order of 1·10³ ergs·cm^–2 in the layer 1000/850 mb, decreasing in the higher layers. The residual dissipation term would indicate a production of kinetic energy, particularly for the layer 500/300 mb in winter. This would appear consistent with results by other authors. Due to the uncertainties inherent in the computational procedures, however, only limited confidence can be given to the absolute values.

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Zusammenfassung Die Kinetische Energie-Bilanz über dem Amerikanischen Mittelmeer während der Winter-(November–April) und Sommerhälfte (Mai-Oktober) des Jahres 1960 wird für die Schichten 1000/350, 850/700, 700/500 und 500/300 mb untersucht. Vertikaltransporte, seitlicher Export und die Produktion von kinetischer Energie werden direkt von den zweimal täglichen Radiosondenaufstiegen berechnet, während die Vernichtung kinetischer Energie als Restglied der Energiegleichung bestimmt wird. Der Energieverbrauch in der Grenzschicht wird unabhängig auf Grund von Schiffsbeobachtungen des Jahres 1960 abgeschätzt. Die Vernichtung kinetischer Energie hat in der Schicht 1000/850 mb die Grössenordnung von 1·10³ ergs·cm^–2·sec^–1, und nimmt nach den höheren Schichten zu ab. Das Restglied der Energiegleichung zeigt eine Produktion kinetischer Energie vor allem für die Schicht 500/300 mb im Winter an. Das erscheint verträglich mit den Ergebnissen anderer Autoren. Wegen der in den Berechnungsverfahren liegenden Unsicherheiten kommt den Absolutwerten nur begrenzte Gültigkeit zu.

     

A propagating fracture model versus a hot spot origin for the Canary islands

The evidence for a hot spot origin for the Canary Islands is reviewed, and it is found that the geochronological and geophysical data do not support this model. The propagating fracture hypothesis explains in a more convincing way the location and chronology of the Archipelago, whose three main periods of activity — corresponding to basal complexes, table-land basalts and recent emissions — are suggested to be related in time and genetically to the three main tensional phases in the nearby High Atlas Mountains.     

A new model for the acquisition of thermoremanence by multidomain magnetite

Isothermal remanence (IRM) induced in multidomain grains at high temperature (T_i) decreases on cooling in zero field. The intensity and stability (against temperature change) of the IRM depend on whether the temperature (T_i) was reached from higher temperature or from lower temperature. These results cannot be explained by the existing multidomain theories. A new model of a thermoremanence (TRM) acquisition mechanism, in which domain wall interactions play the major role, is proposed. This model explains the main features of the experimental results very well, predicting an almost linear relationship between TRM and the inducing field, up to relatively high fields.     

A new velocity model for clay-sand mixtures1

None of the standard porosity-velocity models (e.g. the time-average equation, Raymer's equations) is satisfactory for interpreting well-logging data over a broad depth range. Clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and P-wave transit time. Because clays are composed of fine sheet-like particles, they normally form pores with much smaller aspect ratios than those associated with sand grains. This difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations. A velocity model for Clay–sand mixtures has been developed in terms of the Kuster and Toksöz, effective medium and Gassmann theories. In this model, the total pore space is assumed to consist of two parts: (1) pores associated with sand grains and (2) pores associated with clays (including bound water). The essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays. Because of this, porosity in shales affects elastic compliance differently from porosity in sand-Stones. The predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales.     

Estimates of the energy of surface waves from atmospheric explosions and the source parameters of the Tunguska event

The results of the numerical modeling of experimental concentrated atmospheric explosions, both nuclear and chemical, are presented. The surface pressure spectra are calculated and constraints are gained on their relation to the energy of surface seismic waves and to earthquake magnitudes. For a more accurate determination of the source parameters of the Tunguska event (June 30, 1908), atmospheric explosions at various altitudes and vertical falls of meteoroids are modeled numerically and their seismic effect is estimated.     

基于新型能量插值法精确建立GRACE-only地球重力场模型

本文基于新型能量插值法,利用美国喷气推进实验室(JPL)公布的2008年的GRACE-Level-1B实测数据,反演了120阶GRACE地球重力场.首先,由于GPS轨道测量精度相对较低,通过将K波段测距仪高精度的星间距离观测量插值引入双星动能差中,进而建立了新型能量插值卫星观测方程.其次,详细对比分析了2点、4点、6点和8点能量插值观测方程对地球重力场反演精度的影响.研究结果表明:基于最优的信噪比,6点能量插值公式有利于提高120阶GRACE地球重力场的反演精度.最后,基于美国、欧洲和澳大利亚的GPS/水准观测数据检验了本文新建立的WHIGG-GEGM03S地球重力场模型的正确性和有效性.