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ARQ - SCN - N 03 (1982)

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http://hdl.handle.net/10400.3/4882

Artigos publicados no Número 3 - 1982

CONTEÚDO / CONTENTS:

NOTA DE ABERTURA
Este 3.º número da Série Ciências da Natureza foi exclusivamente destinado aos Proceedings do Simpósio sobre a Actividade de Vulcões Oceânicos que se realizaram nos Açores em Agosto de 1980.
As sessões realizaram-se nas instalações da Universidade dos Açores, em Ponta Delgada, e esta publicação é mais uma colaboração que a Universidade dos Açores dá ao referido Simpósio / J. Ávila Martins, Vasco Garcia

MACHADO, Frederico - Preface. (pp. 11-12)

INTERNATIONAL SYMPOSIUM - On the Activity of Oceanic Volcanoes. (pp. 13-15)

LIST OF PARTICIPANTES (pp. 17-26)

OPENING SESSION

BRYAN, Wilfred B. - Mt. St. Helens, Washington: initial eruptive events and morphologic changes. (pp. 29-36)

SECTION 1 (and 3) - Submarine rift eruptions and oceanic island activity - Convenor: H.-U. SCHMINCKE (University of Bochum, Germany)

CANAS, José A. - Motion of the plates as function of the low-q zones beneath spreading centers. (p. 39)

AVDEIKO, G. P. - Scales of recent submarine volcanism. (pp. 41-42)

URRUTIA-FUCUGAUCHI, J. - Magnetic properties of some tholeiitic basalts dredged from the Gulf of California, Mexico. (pp. 43-44)

TRYGGVASON, EYSTEINN - Observed ground deformation during the Krafla Eruption of March 16, 1980. (pp. 45-56)

BRANDSDÓTTIR, Bryndís; EINARSSON, Páll - Seismic activity and rifting in the Krafla fault swarm in NE-iceland. (pp. 57-58)

NAKAMURA, Kazuaki - Why do long rift zones develop better in Hawaiian volcanoes : a possible role of thick oceanic sediments. (pp. 59-73)

STAUDIGEL, S.; SCHMINCKE, H.-U. - Submarine pyroclastic rocks of the La Palma ‘Ophiolite’ complex. (pp. 75-76)

CAMUS, Guy - Le Capelinhos (Faial, Açores) vingt ans après son eruption : le modele eruptif ‘Surtseyen’ et les anneaux de tufs hyaloclastiques. (pp. 77-81)

HERNANDEZ-PACHECO, Alfredo; VALLS, M. C. - The historic eruptions of La Palma Island (Canaries). (pp. 83-94)

MACHADO, Frederico - Interpretation of ground deformation in the Azores. (pp. 95-112)

SELF, Stephen - The ignimbrites of Terceira, Azores. (pp. 113-114)

PRESTVIK, Tore - The geology, volcanic activity, and age of Bouvetøya, South Atlantic. (pp. 115-123)

BILIK, István - Lower cretaceous submarine rift volcanism in the Southern Transdanubia in Hungary. (pp. 125-126)

FEDOTOV, S. A.; BALESTA, S. T.; GORELCHIK, V. I.; FLEROV, G. B.; ENMAN, V. B. - The large Tolbachik fissure eruption in 1975-1976, Kamchatka. (pp. 127-128)

BELL, J. D.; ATKINS, F. B.; HARRIS, C. - A provisional, geological map of ascension island, South Atlantic.> (p. 129)

SECTION 2 - Petrology and geochemistry of oceanic volcanoes - Convenor: P. E. BAKER (University of Nottingham, United Kingdom)

SCHMINCKE, H.-U.; STAUDIGEL, H.; BREY, G. - Mantle heterogeneity in the North Atlantic : evidence from oceanic islands. (pp. 133-134)

BRYAN, Wilfred B. - Fractionation, partial melting, and mixing in normal basalts from 22 ̴25˚ N, mid-atlantic ridge. (pp. 135-144)

FERNANDEZ, Louis A. - The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores. (pp. 145-158)

MARRINER, Giselle Frances; NORRY, M. J.; GIBSON, I. L. - The petrology and geochemistry of the Água de Pau Volcano, São Miguel, Azores. (pp. 159-173)

STOREY, Michael - Petrogenesis of the recent trachytic pyroclastic succession of Água de Pau Volcano, (São Miguel, Azores). (pp. 175-176)

ARNEY, Barbara - Geochemistry of Eyjafjöll, a volcano in southern Iceland. (pp. 177-178)

JØRGENSEN, Karl A. - Magma mixing and hybridism : a preliminary study from southern Iceland. (pp. 179-194)

GRÖNVOLD, Karl - Krafla lavas 1975-1980 : chemical variation. (pp. 195-196)

SIGVALDASON, Gudmundur E.; OSKARSSON, Niels - Fluorine in volcanic rocks of Iceland. (p. 197-)

FLOWER, Martin F. J. - Magma mixing at oceanic transform fracture zones. (pp. 199-200)

BATIZA, Rodey; O’Hearn, T. - Major element chemistry of basalt glasses dredged from young isolated volcanoes and the East Pacific rise, 10˚ ̴14˚ N. (pp. 201-231)

WOLFF, John A. - Heterogeneity of phonolitic pumice deposits from Tenerife, Canary Islands. (pp. 231-232)

HARRIS, Chris; BELL, J. D.; ATKINS, F. B. - Coarse-Grained rocks from Ascension Island. (pp. 233-246)

MITCHELL-THOME, Raoul C. - On occurrence of vitrophyres in Macaronesia. (pp. 247-248)

FLOWER, Martin F. J. - Plagioclase accumulation and phenocryst reaction in oceanic tholeiite : an indication of spreading rate. (pp.249-250)

KUBOVICS, Imre - Genesis of ultrabasic-basic rocks (‘Ophiolites’) of north Hungary. (pp. 251-252)

ARAMAKI, Shigeo - Submarine volcanoes East and South of Izu Peninsula, Central Japan. (pp. 253-254)

BAKER, P. E.; KEYVAN-SCOCOUHI, F. A. - Petrology and geochemistry of the Juan Fernandez Islands, South East Pacific. (pp. 255-264)

SECTION 4 - Geothermal power development in oceanic areas - Convenor: V. H. FORJAZ (University of Lisbon, Portugal)

ANDLAUER, Gerard - Projet de saline a Ribeira Grande. (p. 267)

FILIPPO, M., TORO, B. - Gravity residual anomalies and geothermics in Latium region (Central Italy). (pp. 269-270)

GORSHKOV, A. P.; GAVRILENKO, G. M.; SELIVERSTOV, N. I.; SCRIPKO, K. A. - Geologic structure and fumarolic activity of the Esmeralda submarine volcano. (pp. 271-298)

CATALDI, R.; FERRARA, G. C.; FUNICELLO, R.; LOVARI, F. - A new case history of geothermal exploration in volcanic areas : the latera field (Northern Latium, Italy). (pp. 299-300)

BENCINI, A.; MARTINI, M.; PICCARDI, G. - New investigations on thermal manifestations of S. Miguel (Azores). (pp. 301-312)

EXCURSION GUIDES FOR THE FIELDS TRIPS

MARTINS, J. Ávila - Excursion guide for field trip V1 : ‘Island of São Miguel’. (pp. 315-328)

SELF, Stephen - Excursion guide for field trip V2 : ‘Island of Terceira’. (pp. 329-342)

MACHADO, Frederico - Excursion guide for field trip V3 : ‘Islands of Fayal and Pico’. (pp. 343-349)

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  • Proceedings of the Symposium on the Activity of Oceanic Volcanoes : Preface
    Publication . Machado, Frederico, org.
    This Symposium was held at the Azores University, in Ponta Delgada, from 4 to 9 August, 1980. […].
    1982-07Journal article Open access Show more
  • Mt. St. Helens, Washington : initial eruptive events and morphologic changes
    Publication . Bryan, Wilfred B.
    After a week of increasing seismic activity, on March 27, 1980, Mt. St. Helens erupted ash and steam to a height of some 2000 m above the new summit crater. This eruption broke a 125-year period of dormancy for this volcano, which had become a popular scenic attraction and center d outdoor recreational activity in the south western corner of the state of Washington. The U.S. Geological Survey hastily called in experts from Denver, Menlo Park, and the Hawaiian volcano observatory, and geologists and volcanologists converged on the mountain from all over the world. Toward the middle d April the frequency of eruptions declined, and local newspapers and television stations confidently reported that the eruptions were over, and that scientists were packing up and leaving. However, the U.S. Geological Survey continued to monitor a bulge on the north flank of the volcano, which grew outward at up to 2 m per day. Small phreatic eruptions took place again from May 7 to May 14, while growth of the bulge continued at a nearly constant rate. On the morning of May 18, a major eruption destroyed the summit and north flank of the mountain. In intensity and volume of material involved, this eruption appears to be equivalent to the 79 a.d. eruption of Vesuvius that destroyed Pompeii. Although the remote location of Mt. St. Helens prevented major loss d life, about 60 people are known dead or remain unaccounted for as a result of this eruption. This note summarizes observations d eruptive activity and morphologic changes in the volcano up to the eruption of May 18. Reference data include both aerial and ground based still photography and sketches, and 16 mm mode film taken from a U.S. Geological Survey observation camp about 15 km northwest d the mountain. Additional background data and details of eruptions and compositions of eruptive products through, August 1980, are given by Hoblitt et al., 1980.
    1982-07Journal article Open access Show more
  • CANAS, José A. (1982). Motion of the plates as function of the low-q zones beneath spreading centers. "Arquipélago. Série Ciências da Natureza", 3: 39.
    Publication . Canas, José A.
    Fundamental-mode Rayleigh waves generated by several earthquakes situated along great circle paths between pairs of seismograph stations on the American and European coastal regions and on Atlantic islands have been analyzed to obtain anelastic attenuation coefficients. Inversion of the attenuation data yield a model for the Mid-Atlantic Ridge. The mean results obtained in this study are: (1) A strong low-Q zone is situated in the upper mantle beneath the bottom of the lithosphere (2) the bottom of the Asthenosphere is situated at a depth of around 250 km. Comparison of the above results with earlier studies in the Pacific Ocean suggest that the velocity of plate motion is slower when attenuation coefficients and internal friction values are smaller and vice versa.
    1982-07Journal article Open access Show more
  • Scales of recent submarine volcanism
    Publication . Avdeiko, G. P.
    Submarine volcanic activity is confined to (1) rift zones of mid-ocean ridges (MOR) and transform faults, (2) hot spots (HS) and belts of hot spots («hot lines »), (3) systems of island arcs (IA) and (4) marginal seas (MS). Volcanic activity may occur on the oceanic flanks of deep sea trenches and marginal swells between trenches and the ocean floor. Rift zones of MOR exhibit the deep-sea fissure eruptions of low-potassium oceanic tholeiites with some variations of mineralogical and chemical compositions. They produce pillow and ropy flows, volcanic cones generally being not formed. As a result of these eruptions, more than 1 X 10¹⁰ t of lava per year pour out on the ocean floor. […].
    1982-07Journal article Open access Show more
  • Magnetic properties of some tholeiitic basalts dredged from the Gulf of California, Mexico
    Publication . Urrutia-Fucugauchi, J.
    This study is based on dredged samples collected from the mouth of the Gulf of California, a young opening oceanic basin. The samples are distributed between the East Pacific Rise crest and the Baja California continental slope. Ages are assigned on their position relative to magnetic anomalies and bathymetric profiles. Results from (1) non-destructive measurements, e.g. NRM intensity and direction, initial susceptibility, magnetic anisotropy and viscosity effects; (2) semi-destructive measurements, e.g. ARM acquisition and AF demagnetization of NRM and ARM; and (3) destructive measurements, e.g. viscous-partial TRM acquisition, are presented. Geochemical results of major and trace elements, including REE, are also presented. The samples show increasing alteration effects and enrichment of light-REE with distance away from the rise crest. Among the results we may mention: (1) the intensity pattern does not conform that usually expected for profiles normal to spreading centers; (2) low temperature weathering is of considerable importance, and its effects correlate well with time; (3) viscous effects at high temperatures (up to 200-300° C) are important in controlling the intensity pattern; and ( 4) magnetic anisotropy may constitute an alternative feature for determining orientation of dredged basalts.
    1982-07Journal article Open access Show more
  • Observed ground deformation during the Krafla eruption of March 16, 1980
    Publication . Tryggvason, Eysteinn
    The Krafla volcano has been monitored with continuously recording tiltmeters and seismometers and frequent geodetic measurements since the beginning of the present episode of activity in 1975. The inflation-deflation sequence of the volcano showed striking regularity in 1977 and 1978 but it became more erratic in late 1979 with slow inflation interrupted by small deflations. The eruption of March 16, 1980 was preceded by rapid deflation which started at 15:15 (GMT) and intense volcanic tremor started simultaneously. The subsidence became very rapid at about 16:00, about three times more rapid than had been seen in any previous subsidence event. The eruption was first seen at about 16:20, but it may have started 10 to 20 minutes earlier. It lasted until about 22h that same night. The deflation of the volcano ceased at about 03h next morning, March 17, and a new inflation started within a few hours. Tilt observations indicate that roughly 30 x 106m3 of magma left the Krafla magma chamber, but only some 10 % of this carne to the surface as very fluid basaltic lava. New fissures extended through the Krafla volcano over a distance of a:bout 21 km and the widening od' the fissure zone was about 1.5 m.
    1982-07Journal article Open access Show more
  • Seismic activity and rifting in the Krafla fault swarm in NE-Iceland
    Publication . Brandsdóttir, Bryndís; Einarsson, Páll
    The Krafla volcano in the rift zone of NE-Iceland has been going through a series of inflation-deflation cycles since 1975. Magma accumulates beneath the volcano during slow inflation periods and is injected laterally into the Krafla fault swarm during deflation events. Each deflation event has a characteristic pattern of seismic activity. It typically begins with continuous volcanic tremor and the tremor amplitude is dependent on the rate of deflation. Earthquake activity increases shortly after the deflation starts and the epicentral area is soon extended from the caldera region, along the fault swarm to the north, the south or both. The propagation speed of the seismic activity is highest in the beginning, but decreases with decreasing deflation rate and increasing length of the epicentral zone. Typical speed is 0.5 m/s, but may reach values as high as 1.2 m/s. […].
    1982-07Journal article Open access Show more
  • Why do long rift zones develop better in Hawaiian volcanoes : a possible role of thick oceanic sediments
    Publication . Nakamura, Kazuaki
    Rift zones are one of the characteristic features of Hawaiian volcanoes. They are long narrow zones of flank fissure eruptions but are distinct from ordinary flank eruption sites on po1ygenetic volcanoes in that eruptions, and therefore dike intrusions, occur repeatedly at the same general place for a long time and thus cause a considerable distance of horizontal spreading. This spreading should somehow be accommodated and the direction of the minimum compressive stress should remain the same after accommodation in order for a new dike to intrude in the same orientation. The Krafla spreading events in Iceland between North American and European plates revealed that the process of the lithospheric spreading is similar to that observed for Hawaiian volcanic activities, including rift zone eruptions. Accreting plate boundaries may be understood as consisting of chain of linear rift zones and their source polygenetic centers where the magma supplied from the asthenosphere is temporarily .stored. Horizontal spreading caused by repeated dike intrusions has been accommodated in the case of the accreting plate boundaries by the lateral separation of lithosphere over astenosphere. In the case of Hawaii sliding of the volcanic edifice over deep sea sediments may be the analogous mechanism such as appears to have occurred during the 1975 Kalapana earthquake which was anticipated by SWANSON et al. (1976) as one of the repeated events as the east rift zone has continuously dilated. Lack of rift zones in otherwise similar Galapagos shields which sit over the young ocean floor with higher relief is consistent with this view.
    1982-07Journal article Open access Show more
  • Submarine pyroclastic rocks of the La Palma «Ophiolite» complex
    Publication . Staudigel, S.; Schmincke, H.-U.
    The basement of La Palma (Canary Islands) consists of plutonic and hypabyssal intrusive and a submarine series, 2.5 km thick. Pyroclastic rocks increase in thickness upwards in the section and dominate at the top where they are several 100 meters thick. The clastic rocks in the pillow-dominated section are well bedded to cross-bedded hyaloclastites forming layers generally < 2 m thick, and thicker beds (up to 5 m) of coarse breccias which range from incipiently fractured pillows, that came to rest nearly in situ, to coarse, well sorted breccias deposited some distance from their source. Clastic rocks in the upper section are massive to poorly bedded, dominantly lapilli- to sand-sized whit clasts, being generally highly vesicular and larger fragments being reddish oxidized displaying shapes and vesicularity intermediate between pillows and sub-aerial scoria. […].
    1982-07Journal article Open access Show more
  • Le Capelinhos (Faial, Açores) vingt ans après son eruption : le modele eruptif ‘Surtseyen’ et les anneaux de tufs hyaloclastiques
    Publication . Camus, Guy
    En août 1978, vingt ans après son éruption le Capelinhos était amputé par l'érosion marine et éolienne de plus de la moitié de sa surface initiale. Les coupes observables dans les falaises permettent de corréler les phases d'1activilté observées lors de l'éruption et les facies des produits ainsi que leur disposition.
    1982-07Journal article Open access Show more