An integrated dynamic model for the volcanic activity at Poas volcano,Costa Rica     

L. Casertano  A. Borgia  C. Cigolini  L. D. Morales  W. Montero  M. Gomez  J. F. Fernandez 《Bulletin of Volcanology》1987,49(4):588-598

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Dynamics of lava flow fronts, Arenal Volcano, Costa Rica     

Andrea Borgia  Scott Linneman  Daniel Spencer  Luis Diego Morales  Jose Brenes Andre 《Journal of Volcanology and Geothermal Research》1983,19(3-4)

Arenal Volcano has effused basaltic andesite lava flows nearly continuously since September, 1968. The two different kinds of material in flows, lava and lava debris, have different rheologic properties and dynamic behavior. Flow morphology depends on the relationship between the amount and distribution of the lava and the debris, and to a lesser extent the ground morphology.Two main units characterize the flows: the channel zone and the frontal zone. The channel zone consists of two different units, the levées and the channel proper. A velocity profile in the channel shows a maximum value at the plug where the rate of shear is zero, and a velocity gradient increasing outward until, at the levées, the velocity becomes zero. Cooling produces a marked temperature gradient in the flow, leading to the formation of debris by brittle fracture when a critical value of shear rate to viscosity is reached. When the lava supply ceases, much of this debris and part of the lava is left behind after the flow nucleus drains out, forming a collapsed channel.Processes at the frontal zone include levée formation, debris formation, the change in shape of the front, and the choice of the flow path. These processes are controlled primarily by the rheological properties of the lava.Frontal zone dynamics can be understood by fixing the flow front as the point of reference. The lava flows through the channel into the front where it flows out into the levées, thereby increasing the length of the channel and permitting the front to advance. The front shows a relationship of critical height to the yield strength (τ₀) surface tension, and slope; its continued movement is activated by the pressure of the advancing lava in the channel behind. For an ideal flow (isothermal, homogeneous, and isotropic) the ratio of the section of channel proper to the section of levées is calculated and the distance the front will have moved at any time t_x can be determined once the amount of lava available to the front is known. Assuming that the velocity function of the front {G(t)} during the collapsing stage is proportional to the entrance pressure of the lava at the channel-front boundary, an exponential decrease of velocity through time is predicted, which shows good agreement with actual frontal velocity measurements taken on two flows. Local variations in slope have a secondary effect on frontal velocities.Under conditions of constant volume the frontal zone can be considered as a machine that consumes energy brought in by the lava to perform work (front advancement). While the front will use its potential energy to run the process, the velocity at which it occurs is controlled by the activation energy that enters the system as the kinetic energy of the lava flowing into the front. A relation for the energy contribution due to frontal acceleration is also derived. Finally the entrance pressure, that permits the front to deform, is calculated. Its small value confirms that the lava behaves very much like a Bingham plastic.  相似文献   

Cooling rate effect as a cause of systematic overestimating of the absolute Thellier paleointensities: A cautionary note     

J. Morales  A. Goguitchaichvili  J. Urrutia-Fucugauchi 《Studia Geophysica et Geodaetica》2007,51(2):315-326

Cooling rate (CR) effects on the intensity of thermoremanent magnetization has been documented for archaeomagnetic materials, where cooling in laboratory conditions is generally much faster compared to natural cooling rates. Since the latter condition also applies to many volcanic rocks, we have investigated in this study the influences of the CR on the determination of absolute paleointensity using recent basaltic rocks. We used magnetically and thermally stable samples mainly containing Ti-poor pseudo-singledomain titanomagnetites (the most widely used material for Thellier paleointensity experiments). These samples previously succeed in retrieving the strength of laboratory field intensities with the Coe’s version of the Thellier method in a simulated paleointensity experiment using similar cooling rates. Our experimental results indicate that the cooling rate effects produce systematic and significant overestimates of the absolute intensity up to 70%. The effect can be much larger than predicted by Neél theory for non-interacting single-domain grains.  相似文献   

The relative locations of multiplets in the vicinity of the Western Almería (southern Spain) earthquake series of 1993–1994     

Daniel Stich  Gerardo Alguacil  José Morales 《Geophysical Journal International》2001,146(3):801-812

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A summary of sulfur dioxide emission rate measuremnts from Guatemalan volcanoes     

RJ Andres  WI Rose  RE Stoiber  SN Williams  O Matías  R Morales 《Bulletin of Volcanology》1993,55(5):379-388

Measurements of the sulfur dioxide (SO₂) emission rate from three Guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measured SO₂ emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO₂ emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO₂ emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recent SO₂ emission rate measurements support laboratory simulation studies of strombolian eruptions; these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions.Average SO₂ emission rates over the last 20 years for Santiaguito, Fuego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global scale, these three volcanoes account for 1% of the annual global volcanic output of SO₂. Santiaguito and Pacaya, together, emit 6% of the total annual SO₂ emitted by continuously erupting volcanoes.Even though SO₂ measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a useful baseline by which to judge future changes. A more complete record of SO₂ emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on Guatemalan society.  相似文献   

Synoptic and mesoaerological study of radiation fog     

Morales  C. 《Meteorology and Atmospheric Physics》1958,10(4):387-409

Summary The present study was for the purpose of determining the conditions necessary to the formation of radiation fog. The temperature and relative humidity of the lowest stratum of the troposphere were sounded with a tethered balloon and radiosonde during a number of nights when the conditions were considered favourable for the formation of radiation fog: clear weather with effective net radiation, light wind, and high relative humidity at ground level. Advection fog was also studied on some occasions for comparison. The measurements were carried out in Uppsala. Meteorological phenomena of possible importance to the study were recorded concurrently with the measurements. The weather was analyzed synoptically and aerologically also on each occasion.The results of the investigation suggest that the conditions necessary to the formation of radiation fog are not only an effective net radiation, light wind, and high relative humidity at ground level, but also that the wind must be light and the relative humidity high at some distance above the ground. This permits the more or less marked surface inversion to leave ground level and to rise as a layer of rapid temperature transition. This is brought about by the radiation gradually emitting from the upper surface of the layer of mist or fog, formed in the lowest and chilled air strata, which are subsequently cooled from above until an unstable lapse rate develops. As a results, the layer of rapid temperature transition is maintained rather intact as it rises. If the radiation continues without obstruction and the wind is ligh aloft, this layer migrates upwards until it reaches a level at which the relative humidity is so low that the cooling necessary for condensation does not occur by radiation, limiting the extension of the underlying fog. If the relative humidity is high only in the undermost air strata, the surface inversion cannot leave ground level and no fog will be formed aloft. If the wind is strong aloft, the process is hindered by the increased turbulent exchange occurring between the high and low strata.

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Zusammenfassung Die vorliegende Untersuchung, die in Uppsala durchgeführt wurde, hat zum Zweck, die für die Bildung von Strahlungsnebel notwendigen Bedingungen festzulegen. Temperatur und relative Feuchtigkeit der untersten Troposphärenschicht wurden mit Fesselballon und Radiosonde während einer Anzahl Nächte ausgemessen, in denen die Bedingungen für die Bildung von Strahlungsnebel günstig erschienen, somit bei klarem Wetter mit effektiver Ausstrahlung, leichtem Wind und hoher relativer Feuchtigkeit am Boden. Zum Vergleich wurden auch einige Fälle von Mischungsnebel (Advektionsnebel) untersucht. Die Bestimmungen wurden in Uppsala durchgeführt. Gleichzeitig wurden auch weitere meteorologische Vorgänge, die für diese Untersuchung von Bedeutung sein konnten, aufgezeichnet. Zudem wurde das Wetter synoptisch und aerologisch bei jeder Gelegenheit un tersucht.Die Ergebnisse dieser Untersuchung legen die Annahme nahe, daß die für die Bildung von Strahlungsnebel not wendigen Bedingungen nicht nur in effektiver Ausstrahlung, leichtem Wind und hoher relativer Feuchtigkeit am Boden bestehen, sondern daß auch in gewisser Entfernung über dem Boden der Wind schwach und die Feuchtigkeit hoch sein muß. Dadurch wird es der mehr oder weniger ausgesprochenen Bodeninversion ermöglicht, das Bodenniveau zu verlassen und als Schicht eines schnellen Temperaturüberganges in die Höhe zu steigen. Dies wird bewirkt durch die Ausstrahlung, die allmählich von der Oberseite der Nebelschicht ausgeht, welche sich in den untersten und ausgekühlten Luftschichten bildet, die sich nach und nach von oben her abkühlen, bis sich ein instabiler Temperaturgradient entwickelt. Infolgedessen wird die Schicht des schnellen Temperaturübergangs beim Emporsteigen nahezu unverändert aufrechterhalten. Falls die Ausstrahlung ungehindert andauert und der Wind auch in der Höhe schwach ist, wandert diese Schicht aufwärts, bis sie ein Niveau erreicht, wo die relative Feuchtigkeit so niedrig ist, daß die für Kondensation notwendige Abkühlung nicht mehr durch die Ausstrahlung hervorgerufen wird, wodurch die Ausdehnung des darunter liegenden Nebels begrenzt wird. Wenn dagegen die relative Feuchtigkeit nur in den alleruntersten Luftschichten hoch ist, kann die Bodeninversion die Höhe des Erdbodens nicht verlassen und es bildet sich haher in der Höhe kein Nebel. Falls in der Höhe starker Wind weht, wird der Prozeß der Nebeldung durch die verstärkten Austauschvorgänge zwischen den hohen und den niederen Schichten verhindert.

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Résumé Le but de la présente étude faite à Uppsala est de déterminer les conditions de formation du brouillard de rayonnement. On a mesuré à cet effet la température et l'humidité relative des couches basses de la troposphère à l'aide de ballons captifs et de radiosondes pendant un certain nombre de nuits apparement favorables à la formation de brouillard, done par temps clair, vent faible et forte humidité au sol. Quelques cas de brouillard d'advection ont été aussi retenus à titre de comparaison. En même temps on a relevé d'autres processus météorologiuqes pouvant être utiles; la situation météorologique fit l'objet d'une analyse synoptique et aérologique dans chaque cas.Les résultats obtenus font penser que ce ne sont pas seulement le rayonnement, la faible agitation de l'air et la forte humidité relative au sol qui sont déterminants dans la formation du brouillard; le vent doit être faible et l'humidité élevée également à une certaine hauteur au-dessus du sol: c'est alors que l'inversion plus ou moins prononcée peut s'élever. Cela résulte du refroidissement par rayonnement de la surface du brouillard bas; la couche froide au sol augmente alors d'épaisseur jusqu'à ce qu'un gradient vertical instable apparaisse. La couche de décroissance rapide de température se maintient tout en gagnant vers le haut, et le processus ne s'arrête que lorsqu'un niveau à faible humidité est atteint; la couche de brouillard a alors acquis son épaisseur maximum. Si l'humidité relative n'est forte que dans les couches les plus basses, l'inversion ne peut par contre quitter le sol et il ne se forme pas de brouillard plus haut. S'il y a du vent fort a une certaine hauteur, le processus de formation du brouillard est rendu impossible par le brassage des couches basses et moyennes.

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With 12 Figures

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Dedicated to Dr.Anders K. Ångström on the occasion of his 70th birthday.  相似文献   

A description of how metal pollution occurs in the Tinto-Odiel rias (Huelva-Spain) through the application of cluster analysis   总被引：3，自引：0，他引：3  

Grande JA  Borrego J  Morales JA  de la Torre ML 《Marine pollution bulletin》2003,46(4):475-480

In the last few decades, the study of space-time distribution and variations of heavy metals in estuaries has been extensively studied as an environmental indicator. In the case described here, the combination of acid water from mines, industrial effluents and sea water plays a determining role in the evolutionary process of the chemical makeup of the water in the estuary of the Tinto and Odiel Rivers, located in the southwest of the Iberian Peninsula.Based on the statistical treatment of the data from the analysis of the water samples from this system, which has been affected by processes of industrial and mining pollution, the 16 variables analyzed can be grouped into two large families. Each family presents high, positive Pearson r values that suggest common origins (fluvial or sea) for the pollutants present in the water analyzed and allow their subsequent contrast through cluster analysis.  相似文献   

The relation of meridional pressure gradients to North Atlantic deep water volume transport in an ocean general circulation model     

Alexa Griesel  Miguel Angel Morales Maqueda 《Climate Dynamics》2006,26(7-8):781-799

We use a coarse resolution ocean general circulation model to study the relation between meridional pressure and density gradients in the Southern Ocean and North Atlantic and the Atlantic meridional overturning circulation. In several experiments, we artificially modify the meridional density gradients by applying different magnitudes of the Gent–McWilliams isopycnal eddy diffusion coefficients in the Southern Ocean and in the North Atlantic and investigate the response of the simulated Atlantic meridional overturning to such changes. The simulations are carried out close to the limit of no diapycnal mixing, with a very small explicit vertical diffusivity and a tracer advection scheme with very low implicit diffusivities. Our results reveal that changes in eddy diffusivities in the North Atlantic affect the maximum of the Atlantic meridional overturning, but not the outflow of North Atlantic Deep Water into the Southern Ocean. In contrast, changes in eddy diffusivities in the Southern Ocean affect both the South Atlantic outflow of North Atlantic Deep Water and the maximum of the Atlantic meridional overturning. Results from these experiments are used to investigate the relation between meridional pressure gradients and the components of the Atlantic meridional overturning. Pressure gradients and overturning are found to be linearly related. We show that, in our simulations, zonally averaged deep pressure gradients are very weak between 20°S and about 30°N and that between 30°N and 60°N the zonally averaged pressure grows approximately linearly with latitude. This pressure difference balances a westward geostrophic flow at 30–40°N that feeds the southbound deep Atlantic western boundary current. We extend our analysis to a large variety of experiments in which surface freshwater forcing, vertical mixing and winds are modified. In all experiments, the pycnocline depth, assumed to be the relevant vertical scale for the northward volume transport in the Atlantic, is found to be approximately constant, at least within the coarse vertical resolution of the model. The model behaviour hence cannot directly be related to conceptual models in which changes in the pycnocline depth determine the strength of Atlantic meridional flow, and seems conceptually closer to Stommel’s box model. In all our simulations, the Atlantic overturning seems to be mainly driven by Southern Ocean westerlies. However, the actual strength of the Atlantic meridional overturning is not determined solely by the Southern Ocean wind stress but as well by the density/pressure gradients created between the deep water formation regions in the North Atlantic and the inflow/outflow region in the South Atlantic.  相似文献   

Uncertainties in projected impacts of climate change on European agriculture and terrestrial ecosystems based on scenarios from regional climate models     

J. E. Olesen  T. R. Carter  C. H. Díaz-Ambrona  S. Fronzek  T. Heidmann  T. Hickler  T. Holt  M. I. Minguez  P. Morales  J. P. Palutikof  M. Quemada  M. Ruiz-Ramos  G. H. Rubæk  F. Sau  B. Smith  M. T. Sykes 《Climatic change》2007,81(1):123-143

The uncertainties and sources of variation in projected impacts of climate change on agriculture and terrestrial ecosystems depend not only on the emission scenarios and climate models used for projecting future climates, but also on the impact models used, and the local soil and climatic conditions of the managed or unmanaged ecosystems under study. We addressed these uncertainties by applying different impact models at site, regional and continental scales, and by separating the variation in simulated relative changes in ecosystem performance into the different sources of uncertainty and variation using analyses of variance. The crop and ecosystem models used output from a range of global and regional climate models (GCMs and RCMs) projecting climate change over Europe between 1961–1990 and 2071–2100 under the IPCC SRES scenarios. The projected impacts on productivity of crops and ecosystems included the direct effects of increased CO₂ concentration on photosynthesis. The variation in simulated results attributed to differences between the climate models were, in all cases, smaller than the variation attributed to either emission scenarios or local conditions. The methods used for applying the climate model outputs played a larger role than the choice of the GCM or RCM. The thermal suitability for grain maize cultivation in Europe was estimated to expand by 30–50% across all SRES emissions scenarios. Strong increases in net primary productivity (NPP) (35–54%) were projected in northern European ecosystems as a result of a longer growing season and higher CO₂ concentrations. Changing water balance dominated the projected responses of southern European ecosystems, with NPP declining or increasing only slightly relative to present-day conditions. Both site and continental scale models showed large increases in yield of rain-fed winter wheat for northern Europe, with smaller increases or even decreases in southern Europe. Site-based, regional and continental scale models showed large spatial variations in the response of nitrate leaching from winter wheat cultivation to projected climate change due to strong interactions with soils and climate. The variation in simulated impacts was smaller between scenarios based on RCMs nested within the same GCM than between scenarios based on different GCMs or between emission scenarios.  相似文献   

Relationship between waterfowl and the seagrassRuppia maritima in a Southwestern Atlantic coastal lagoon     

Alejandro Bortolus  Oscar O. Iribarne  Mariano M. Martínez 《Estuaries and Coasts》1998,21(4):710-717

We evaluated the distribution of waterfowl in relation to a seagrass (Ruppia maritima) patch, to infauna, and on its relationship with substrate characteristics. An experiment performed in the Mar Chiquita coastal lagoon (37°46′S, 57°27′W; Argentina) was used to evaluate the effect of herbivory on widgeon grass,R. maritima. Control plots of equal size, located between bird exclosures, were exposed to herbivory. The experiment ran for 31 d, starting on December 1, 1994. Censuses showed that black-necked swan ( $\bar x = 50$ birds ha^?1, SD = 37, n = 10) and coots ( $\bar x = 42$ birds ha^?1, SD = 28, n = 10) were the most important (always present) of the waterfowl seen feeding onR. maritima. The results of the experiment showed greater leaf lengths, lower belowground (rhizomes and roots) biomass, greater aboveground (leaves and shoots) biomass, and greater abundance of the polychaeteHeteromastus similis in exclosure plots. There were no exclosure effects on total biomass (belowground plus aboveground), reproductive parts (fruits and pre- and postpollination flowers), or abundance of most benthic infauna. Topographic surveys showed that sediment surface was higher within theR. maritima patches, but there were no significant differences in granulometric composition. Surveys also showed that bird distribution was strongly associated with the presence ofR. maritima.  相似文献