The Hekla eruption 1980–1981

The sixteenth eruption of Hekla since 1104 began on August 17th, 1980, after the shortest repose period on record, only ten years. The eruption started with a plinian phase and simultaneously lava issued at high rate from a fissure that runs along the Hekla volcanic ridge. The production rate declined rapidly after the first day and the eruption stopped on August 20th. A total of 120 million m³ of lava and about 60 million m³ of airborne tephra were produced during this phase of the activity. In the following seven months steam emissions were observed on the volcano. Activity was renewed on April 9th 1981, and during the following week additional 30 million m³ of lava flowed from a summit crater and crater rows on the north slope. The lavas and tephra are of uniform intermediate chemical composition similar to that of earlier Hekla lavas. Although the repose time was short the eruptions fit well into the behaviour pattern of earlier eruptions. Distance changes in a geodimeter network established after the eruptions are interpreted as due to inflation of magma reservoirs at 7–8 kilometers depth.     

On the rate of lava- and tephra production and the upward migration of magma in four icelandic eruptions

The rate of the lava production of three Icelandic fissure eruptions (Lakagigar 1783, Hekla 1947, Askja 1961) is calculated and an attempt is made at a reasonable approximation of the rate of lava production per length and width of the feeding fissures and the rate of upward migration of the magma through the fissures. The results are summed up in Table 2. The figures for the maximum upward migration there presented should be regarded as minimum figures. As a comparison with the mainly lava producing fissure eruptions the tephra production of the acid and highly explosive Askja eruption of 1875 is discussed. It has hitherto been assumed that the enormous amount of tephra, about 2 km₃, which was produced by this eruption in 8 1/2 hours, came entirely from the Viti crater, but with regard to its small diameter it seems likely that the very fine grained tephra produced during the first hours of the eruption was partly expelled from nearby fissures now covered by Lake Öskjuvatn.

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Zusammenfassung Die Rate der Lavaförderung bei drei isländischen Spalteneruptionen (Lakagigar 1783, Hekla 1947, Askja 1961) wird errechnet, und es wird versucht, einen Annäherungswert zu gewinnen über die Rate der Lavaförderung, bezogen auf Länge und Weite der Zuführungsspalten und die Rate der Aufwärtsbewegung des Magma durch die Spalten. Die Ergebnisse sind in Tafel 2 zusammengefaßt. Die darin angegebenen Zahlen für die maximale Aufwärtsbewegung sollten als Minimum aufgefaßt werden. Als Vergleich mit den hauptsächlich Lava führenden Spalteneruptionen wird die Tephraproduktion der sauren und hochexplosiven Askja Eruption von 1875 behandelt. Bisher wurde angenommen, daß die enorme Menge Tephra — ungefähr 2 km₃, die diese Eruption in 8 1/2 Stunden hervorbrachte — ausschließlich aus dem Viti Krater kam; aber in Anbetracht seines geringen Durchmessers scheint es wahrscheinlich, daß die sehr feinkörnige Tephra, die während der ersten Stunden der Eruption entstand, teilweise von nahegelegenen Spalten ausgeworfen wurde, die jetzt vom Öskjuvatn-See bedeckt sind.

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Résumé La mesure de production de lave de trois éruptions fissurales de l'Islande (Lakagigar 1783, Hekla 1947, Askja 1961) est calculée et il est essayé de rapprocher la mesure de cette production à l'égard de longueur et largeur des fissures d'alimentation, et la mesure de la migration vers le haut du magma par les fissures. Les résultats sont présentés au tableau 2. Les chiffres de la migration maximum vers le haut doivent être entendus comme minimum. En comparaison avec l'éruption fissurale produisant principalement de la lave, la téphra production de l'acide et fort explosive éruption de l'Askja de 1875 est discutée. On a supposé jusqu'à présent que l'énorme masse de téphra, environ 2 km₃, qui fut produite lors de cette éruption en 8 1/2 heures, provenait seulement du cratére Viti; mais considérant son petit diamètre il est probable que la téphra de grain fin fut en partie lancée par des fissures voisines et qui à présent sont couvertes par le Lac Öskjuvatn.

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(Lakagígar 1783; Hekla 1947; Askja 1961). . Askja 1875 , . .

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday     

Some problems of volcanism in Iceland

Until two decades or so ago the petrography of Iceland seemed to present a rather simple picture. About 99 per cent of the rocks were regarded as basaltic, 1 per cent as rhyolitic and rocks of intermediate composition as nearly non-existent. Recent research has changed this picture. Central volcanoes producing acid and intermediate lava and tephra have played a considerable role both in the Tertiary and Quaternary. Contrary to the lava massproducing basalt volcanoes, fed by a deep-seated and rather uniform basalt magma source, the differentiated central volcanoes are normally fed by separated magma chambers at smaller depth, where differentiation takes place between the eruptions, resulting in intermediate and acid products which bridge the immiscibility gap between the basalts and the rhyolites. Eight to ten per cent of the postglacial lavas and tephras and about 25 per cent of the historical ones are acid or intermediate.Opinions still differ as to whether the existence of these rocks can be explained solely as the result of gravitational differentiation of parent basalt magma or has to be explained partly by a remelting of a continental layer beneath the plateau-basalts. There are, however, some rather strong geological evidences in favour of the existence of such a layer and they seem at the moment not to be contradicted by geophysical research.The Surtsey eruption has demonstrated the close relation between the craterrows, shieldvolcanoes and tablemountains and convincingly shown how greatly external circumstances may influence volcanic activity and the shape of a volcano. The eruption focused interest on the neovolcanic zone of Iceland as a supra marine part of the Mid-Atlantic rift-ridge zone, where volcanic activity has taken place under similar conditions as along its submarine parts, viz. under water (glacial meltwater) when the Pleistocene ice-sheets blanketed the volcanic activity. Similar morphological types of volcanoes can therefore be expected in both cases, viz. steepsided mounds and long steepsided ridges.

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Zusammenfassung Bis vor ungefähr zwei Jahrzehnten schien die Petrographie Islands ein verhältnismäßig einfaches Bild zu bieten. Etwa 99% des Gesteins wurde für basaltisch, 1% für rhyolithisch, und Gesteine von intermediärer Zusammensetzung für fast nicht existent gehalten. Die jüngste Forschung hat dieses Bild gewandelt. Zentralvulkane, die saure und intermediäre Lava und Tephra ausstoßen, haben im Tertiär wie auch im Quartär eine erhebliche Rolle gespielt. Im Gegensatz zu den Basaltvulkanen, welche von einer tiefgelegenen und ziemlich einheitlichen Basaltmagmaquelle gespeist werden und Lava in Massen ausstoßen, werden die differenzierten Zentralvulkane normalerweise von getrennten Magmakammern in geringerer Tiefe gespeist, wo eine Differentiation zwischen den Eruptionen stattfindet. Es entstehen intermediäre und saure Materialien, die die Immiszibilitätslücke zwischen den Basalten und den Rhyolithen überbrücken. 8–10% der postglazialen Laven und Tephren und etwa 25% der historischen sind sauer oder intermediär.Die Meinungen gehen noch auseinander hinsichtlich der Frage, ob das Vorkommen dieses Gesteins allein als das Ergebnis einer gravitativen Differentiation des basaltischen Stamm-Magmas erklärt werden kann, oder ob man es teilweise mit einem Wiedereinschmelzen einer Sialschicht unterhalb der Tafelbasalte erklären muß. Es gibt für die Existenz einer solchen Schicht einige ziemlich überzeugende geologische Zeugnisse, und es scheint so, als ob diesen gegenwärtig durch die geophysikalische Forschung nicht widersprochen würde.Die Surtsey-Eruption hat die enge Beziehung zwischen den Kraterreihen, den Schildvulkanen und den Tafelbergen aufgezeigt und überzeugend dargelegt, wie stark äußere Umstände die Vulkantätigkeit und die Form eines Vulkans beeinflussen können. Diese Eruption konzentrierte das Interesse auf die neovulkanische Zone Islands als eines supramarinen Teils des mittelatlantischen Rückens, wo die Vulkantätigkeit während der Glazialperioden der quartären Eiszeit unter ähnlichen Bedingungen stattgefunden hat, wie entlang ihrer submarinen Teile, d. h. unter Wasser (glazialem Schmelzwasser). Man darf deshalb in beiden Fällen ähnliche morphologische Vulkantypen erwarten, d. h. steilwandige Hügel und lange steilwandige Rücken.

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Résumé Vingt ans plus tôt la pétrographie de l'Islande paraissaît assez simple. Les recherches récentes ont changé cette conception. Des volcans centraux ont joué un rôle considérable au Tertiaire et au Quaternaire. Les volcans basaltiques sont nourris par des sources profondes et assez homogénes de magma basaltique. Par contre les volcans centraux sont nourris par des chambres magmatiques moins profondes ou il y a une différenciation des éruptions: il y a des matériaux intermédiaires et acides. 8–10% des laves et tephras postglaciales et 25% des laves et tephras historiques sont acides ou intermédiaires.Les opinions diffèrent encore dans la question si l'existence de ces roches est le résultat d'une différenciation du magma basaltique original ou s'il s'agit d'une refonte d'une couche continentale au-dessous des plateaux basaltiques.L'éruption de Surtsey a démontré la relation étroite entre les chaînes de cratères, les volcans en bouclier et les guyots. Elle montre combien des circonstances extérieures ont influencé l'activité volcanique et la forme d'un volcan Cette éruption attircut l'intérêt vers la zone néo volcanique de l'Islande. C'est la partie supramarine de la faille-dorsale-zone mi-atlantique ou l'activité volcanique a en lieu sous des conditions pareilles à celles de la partie submarine, c'est à dire sous l'eau (eau glaciale). Dans les deux cas on pent supposer de pareils types morphologiques de volcans.

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Modeling discharge rating curves with Bayesian B-splines

River discharges are traditionally modeled by employing a standard power-law methodology. Recently, the Bayesian approached has successfully been applied to improve the estimates of the standard power-law. In this article, an extension to the standard power-law based on Bayesian B-splines is developed and tested on data sets from 61 different rivers. The extended model is evaluated against the standard power-law using two measures, the Deviance Information Criterion and Bayes factor. The extended model captures deviations in the data from the standard power-law but reduces to the standard power-law when that model is adequate. The standard power-law is inadequate for 26% of the rivers while the extended model provides an adequate fit in all of those cases and for the remaining 74% of the rivers the extended model and the power-law model both give adequate fit with almost identical estimates.     

The effect of gross primary production, net primary production and net ecosystem exchange on the carbon fixation by chemical weathering of basalt in northeastern Iceland

The overall objective of this study is to define and interpret the annual dissolved inorganic carbon (DIC) flux in selected river catchments in North Eastern Iceland. The flux stems primarily from chemical weathering of basalt. The DIC flux out of the catchments is compared with the spatial distribution of the various vegetation communities and their gross primary production (GPP), net primary production (NPP) and net ecosystem exchange (NEE). There is no correlation between the DIC flux and the GPP, but one between DIC and NPP. The DIC flux is highly dependent on the NEE, which in turn is governed by the area extent of wetlands in these catchments. A variation by a factor 5 of the NEE results in a variation by a factor 2.8 in the river dissolved inorganic flux.     

Oxygen fugacity control in piston-cylinder experiments: a re-evaluation

Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni–NiO or Co–CoO) and H₂O, with an inner gold–palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010). H₂O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9–10):985–994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333–1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni–NiO and Co–CoO buffers, which is incorrect since the melts are all undersaturated in H₂O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log $a_{{{\text{H}}_{ 2} {\text{O}}}}$ .     

Suspended basaltic glass–seawater interactions

The objective of this study was to quantify by experiments the initial seawater–suspended basaltic glass interactions following the 1996 outburst flood from the Vatnajökull glacier, Iceland. The altered basaltic glass dissolved in seawater as recorded by the Si release from the glass. The dissolved concentrations of Na, Ca, Si, Ba, Cd, Co, Cu, Hg, Mn, Ni and total dissolved inorganic N increased with time but the concentrations of Mg, K, S, Sr, Fe, Pb and Zn decreased. Calculated 1 to 10 day fluxes for Si range from 38,000 tons/day to 70,000 tons/10 days. The fluxes for other major elements are more uncertain, but the positive flux (release from suspended matter to seawater) of Ca and Na, and negative flux of Mg, K and S are greater than the Si flux.