Showing papers in "Bulletin of Volcanology in 1969"
TL;DR: Mayon Volcano, southeastern Luzon, began a series of explosive eruptions at 0900 April 21, 1968, and by May 15 more than 100 explosions had occurred, at least 6 people had been killed, and roughly 100 square km had been covered by more than 5 cm of airfall ash, blocky ash flows, and a lava flow as discussed by the authors.
Abstract: Mayon Volcano, southeastern Luzon, began a series of explosive eruptions at 0900 April 21, 1968, and by May 15 more than 100 explosions had occurred, at least 6 people had been killed, and roughly 100 square km had been covered by more than 5 cm of airfall ash, blocky ash flows, and a lava flow. All material crupted was porphyritic augite-hypersthene andesite.
112 citations
109 citations
TL;DR: In this paper, a simple model based on the hypothesis of sea floor spreading can account for the main features of two major high heat flow anomalies in the eastern Pacific; the broad band of high values along the crest of the East Pacific Rise and the large concentration of high value centered on the Galapagos Rift Zone.
Abstract: A simple model based on the hypothesis of sea floor spreading can account for the main features of two major high heat flow anomalies in the eastern Pacific; the broad band of high values along the crest of the East Pacific Rise and the large concentration of high values centered on the Galapagos Rift Zone. Using the same model to interpret both the surface shape of the midocean ridges and the heat loss of the entire ridge system, the calculated elevation is found to be comparable, though smaller than, that observed for the ridges and the heat dissipated by crustal production along the axis of the entire ridge system is shown to be approximately 15% of the total heat loss through the oceans.
86 citations
TL;DR: Santiaguito, an extrusive domal complex in southwestern Guatemala has recently exhibited renewed domal growth, as much as 50 meters vertically in the first twelve months of growth as mentioned in this paper.
Abstract: Santiaguito, an extrusive domal complex in southwestern Guatemala has recently exhibited renewed domal growth, as much as 50 meters vertically in the first twelve months of growth. Synchronous with this activity, near the other end of the complex 1.3 km distant, there are pyroclastic eruptions. Ninety percent of the extensive hot lumarolic emission at Santiaguito is concentrated near the active pyroclastic vent, although numerous other lumaroles are found including a group of particularly hot vents associated with the current dome extrusion. Description and tabulation of chemical and mineralogical characteristics of sublimates and condensed gas from fumaroles at eight localities on the mountain illustrate the essential similarity and also the minor differences. The differences are in many instances related to volume of gas, the amount of rainwater dilution, and amount of oxidation of the gases along their path.
84 citations
TL;DR: Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km2 as mentioned in this paper, and the rhyolites originated by melting of granitic crustal rocks.
Abstract: Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km2. The rhyolites originated by melting of granitic crustal rocks.
57 citations
TL;DR: In this article, a description of an explosion crater area in the eastern Rift Valley of Northern Tanzania is given, which includes maar-type explosion craters, tuff rings and tuff cones, the location of which is controlled by minor faults on the floor of the Rift Valley.
Abstract: A description is given of an explosion crater area in the eastern Rift Valley of Northern Tanzania. The features comprise maar-type explosion craters, tuff rings and tuff cones, the location of which is controlled by minor faults on the floor of the Rift Valley. In some tuff rings and cones biotite and pyroxene are common, and olivine-biotite pyroxenite is common amongst the ejected blocks. Other blocks are of ijolitic types and spinel harzburgite. The associated lavas are olivine nephelinites and olivine melilitites, which are the sodic analogues of the katungite and ugandite found in the explosion crater area in the western Rift Valley in South-West Uganda.
52 citations
TL;DR: In this article, the results of geological, geochemical and isotopic investigations in the Hengill thermal area in Iceland are presented, which may be regarded as typical of the Icelandic high temperature areas.
Abstract: The results of geological, geochemical and isotopic investigations in the Hengill thermal area in Iceland are presented. This area may be regarded as typical of the Icelandic high temperature areas.
51 citations
TL;DR: The relationship of heat flow to age of the basement rocks has been studied for USA and Canada, Australia and India as mentioned in this paper, and it is found that heat flow values for all continents studied show a definite correlation with age the relatively high heat flow being associated with younger basements.
Abstract: The relationship of heat flow to age of the basement rocks has been studied for USA and Canada, Australia and India. In areas of sedimentary basins the ages of the cores obtained from the metamorphic or igneous basement were used for such correlation. It is found that heat flow values for all continents studied show a definite correlation with age the relatively high heat flow being associated with younger basements. Such correlation when fully established will enable us to correlate heat flow values with geology and ages of tectonic events which have occurred in the earth’s crust.
50 citations
TL;DR: The Miocene sequence of felsic extrusive rocks of about 1000 m total thickness on Gran Canaria is divided into three units: a lower unit of trachytic rhyolites (lavas, composite flows, ignimbrites) characterized by a phenocryst assemblage of anorthoclase (Or15-20, wt%), clinopyroxene, hypersthene, and Fe/Ti-oxides), with minor quartz and aegirine.
Abstract: The Miocene sequence of felsic extrusive rocks of about 1000 m total thickness on Gran Canaria is divided into three units:
a)
A lower unit of trachytic rhyolites (lavas, composite flows, ignimbrites) characterized by a phenocryst assemblage of anorthoclase (Or15–20, wt%), clinopyroxene, hypersthene (amphibole substituted for both in ignimbrites), and Fe/Ti-oxides. The commonest groundmass minerals are anorthoclase and alkali-amphibole, with minor quartz and aegirine.
b)
A middle unit of comenditic and pantelleritic ignimbrites characterized by anorthoclase (Or20–32) and amphibole. Phenocryst minerals restricted to individual flows are Fe/Ti-oxides (several comendites), clinopyroxene, biotite, and sphene. The commonest groundmass minerals are anorthoclase and Tiaegirine, with lesser katophorite, arfvedsonite and quartz.
c)
An upper unit of trachvtic and phonolitic ignimbites and lava flows (normative ne rarety exceeding 10%) with nepheline phonolite lava flows becoming increasingly abundant upwards. The ignimbrites have mostly anorthoclase (Or30-04), and biotite, with rarer Fe/Ti-oxides, hornblende, and clinopyroxene. The commonest groundmass minerals are anorthoclase, aegirine, and alkali-amphiboles, and in some flows nepheline.
46 citations
TL;DR: A dacitic lava flow with a volume of about 24 km3 is described in this article, which is the largest of three lava flows which were erupted in the youngest phase of volcanism.
Abstract: A dacitic lava flow with a volume of about 24 km3 is described. This flow is the largest of three of this type which were erupted in the youngest phase of volcanism in one part of the Andes of northern Chile. The majority of volcanoes erupted during this phase are more andesitic in composition and are made up of small flows and pyroclastic materials.
36 citations
TL;DR: Tectonique as mentioned in this paper describes a fosse centrale etroite visible in the NNW of the Afar region of the Levante, which is conditioned by des fissures de tension ouvertes and des failles normales de direction NNW.
Abstract: Tectonique — Du 15° au 13° parallele, l’apex septentrional de l’Afar est conditionne par des fissures de tension ouvertes et des failles normales de direction NNW. Un graben a fosse centrale etroite est nettement visible sur plusieurs dizaines de km au NNW du lac Giulietti. Ensuite il est cache sous les appareils volcaniques de la Chaine de l’Erta-Alc qui jalonnent l’emplacement de son fosse central. Au-dela, dans la Plaine de Sel, la trace de ce fosse est marquee par l’alignement d’accidents divers (domes de sel, sources carboniques, crateres d’explosion). Au nord de la Plaine de Sel enfin, la Chaine de l’Alid se trouve exactement dans l’alignement du graben.
TL;DR: The Garibaldi Complex is one of a chain of predominantly silicic volcanic cones along the centre of the Main Ethiopian Rift, which form part of the Pleistocene-Recent Aden Series (Mohr, 1962a) as mentioned in this paper.
Abstract: The Garibaldi Complex is one of a chain of predominantly silicic volcanic cones along the centre of the Main Ethiopian Rift, which form part of the Pleistocene-Recent Aden Series (Mohr, 1962a) The present form of the Complex is largely a result of silicic conebuilding episodes, between which ignimbrites were erupted and areas collapsed to form calderas, and to a lesser extent of recent basalt eruptions Comparisons are made with other areas of caldera collapse and attention drawn to the possible relationship between caldera complexes and plutonic ring structures
TL;DR: Inclusions consisting of clinopyroxene, amphibole, Fe-Ti oxides and apatitc are abundant in the Roque Nublo volcanics, a unit of Late Tertiary age that is widespread on Gran Canaria Island as discussed by the authors.
Abstract: Inclusions consisting of clinopyroxene, amphibole, Fe-Ti oxides and apatitc are abundant in the Roque Nublo volcanics, a unit of Late Tertiary age that is widespread on Gran Canaria Island. The unit includes alkalic basalts and breccias. Mafic minerals in several inclusions and in one basalt host have been analysed with the electron microprobe.
TL;DR: In this article, a phreatic explosion occurred in the Larderello geothermal region for the first time in the year 1282 and the causes of these explosions are discussed.
Abstract: Phreatic explosion craters are described for the Larderello geothermal region for the first time. A phreatic explosion occurred in the year 1282. The description given by a contemporary chronicler, probably the first written description of such a phenomenon, is reported. The causes of these explosions are discussed.
TL;DR: More than two hundred new analyses of basaltic rocks from the Canary Islands are presented in this paper, showing that the earlier successions have similar variation trends throughout the archipelago; these trends represent all the intermediate types between basic differentiates (oceanites, ankaramites) and more salic differentiates.
Abstract: More than two hundred new analyses of basaltic rocks from the Canary Islands are presented. The available data show that the earlier successions have similar variation trends throughout the archipelago; these trends represent all the intermediate types between basic differentiates (oceanites, ankaramites) and more salic differentiates (trachy-basalts, hawaiites). In the more recent volcanic series, the study shows that there is a magmatic diversification with different variation trends in the Eastern than in the Central Canary Islands. In the latter the alkaline character becomes stronger in the successive periods of volcanic activity which have been established in each island. In the Eastern islands the basaltic evolution is, on the contrary, towards basaltic rocks with tholeiitic affinities.
TL;DR: In this paper, the mineralogical, textural and chemical features of the dunite, peridotite, pyroxenite and gabbroic inclusions present in the Quaternary basalts of the Canary Islands are discussed.
Abstract: This paper deals with the mineralogical, textural and chemical features of the dunite, peridotite, pyroxenite and gabbroic inclusions present in the Quaternary basalts of the Canary Islands.
TL;DR: A great sequence of hydrothermally altered and tectonically disturbed lavas and breccias is exposed in the erosional cirques of Piton des Neiges volcano, Reunion as discussed by the authors.
Abstract: A great sequence of hydrothermally altered and tectonically disturbed lavas and breccias is exposed in the erosional cirques of Piton des Neiges volcano, Reunion. These rocks are cut by intense swarms of minor intrusives and are overlain by a carapace of younger lavas which date back at least 2 m.y. The older lavas and breccias are believed to have been formed by submarine eruption of basalt magma during the pre-emergent growth stages of the volcano. It is suggested that their subsequent elevation to 2000 m. above sealevel is due to the thrusting of oceanic crust from the north-east, associated with movements along NE-SW fractures in the western Indian Ocean floor.
TL;DR: On the island of Pantelleria (Channel of Sicily) several layers of particular ignimbrites have been found and their properties can be explained only by admitting a great fluidity of the deposited material.
Abstract: On the Island of Pantelleria (Channel of Sicily) several layers of particular ignimbrites have been found. Their properties can be explained only by admitting a great fluidity of the deposited material. Such a low viscosity is abnormal for sodarhyolitic or sodatrachytic melts and demonstrates that the temperature must have been exceptionally high, as it is possible only in the case of contact anatexis.
TL;DR: A cluster of well-preserved recent volcanoes in the northern Bayuda Desert make up a more or less continuous field some 520 km2 in area surrounded by a number of isolated centres of eruption as discussed by the authors.
Abstract: A cluster of well-preserved recent volcanoes in the northern Bayuda Desert make up a more or less continuous field some 520 km2 in area surrounded by a number of isolated centres of eruption. The volcanoes are numerous but small; up to 400 m in height and 0.35 km2 in volume. Most of them are simple composite volcanoes with a pyroclastic cone skirted by a small lava field erupted from the same vent after explosive eruptions had ceased. In a few instances, however, the cone was eviscerated by more violent eruptions, leaving a deep explosion crater. The lavas are all nepheline-normative alkali basalts and contain a variety of xenocrysts and xenoliths from at least three different sources. The distribution of the recent volcanoes was partly controlled by large granitic ring-intrusions of the Basement Complex country rocks. These intrusions belong to the Younger Granite association of late Precambrian or Lower Palaeozoic age and represent a volcanic-intrusive episode widespread in northern Africa. The complexes are composed of cale-alkaline and peralkaline granites and syenites and a related plexus of dyke swarms.
TL;DR: Karroo (Triassic-Jurassic) sediments and lavas occupy a N.N.E-trending trough known as the Tuli Syncline 230 km in length by 45 km wide along the southern margin of Rhodesia as mentioned in this paper.
Abstract: Karroo (Triassic-Jurassic) sediments and lavas occupy a N.N.E.-trending trough known as the Tuli Syncline 230 km in length by 45 km wide along the southern margin of Rhodesia. The structure is fault bounded, especially on the north, and comprises a sequence of gently inward dipping lava flows cut by numerous E-W and N.N.E. striking dolerite dykes. The igneous rocks have been subdivided on the basis of mineralogy and chemistry into a stratigraphic sequence of limburgites near the base, olivine basalts and upper augite-plagio-clase-phyric basalts. In addition, rare shoshonite and absarokite types occur. Twentyfour new silicate analyses are comparable to those from rocks in the neighbouring Nuanetsi Province of Rhodesia, and show strong affinities to the northern province Karroo basalts of southern Africa as defined by Cox,McDonald andHornung (1967).
TL;DR: The late Mesozoic-Tertiary basaltic province of the Aden traps covering many thousands of square miles of south-west Arabia, exhibits a great variety of rocks and structures, which are illustrated in this account by descriptions of three contrasting regions as discussed by the authors.
Abstract: The late Mesozoic-Tertiary basaltic province of the Aden traps covering many thousands of square miles of south-west Arabia, exhibits a great variety of rocks and structures, which are illustrated in this account by descriptions of three contrasting regions.
1)
NearDhala there is more than 3,000 metres of olivine basalt picrite basalt and trachyte, with interbedded agglomerate and ignimbrite, penetrated by a variety of dykes, which include basalt, trachyte and quartz porphyry.
2)
Musaymir, 20 miles SSW of Dhala, has near horizontal non-olivine basalt and trachyte lavas, with interbedded ignimbrite, and numerous dykes. Of the latter basaltic types have a NW trend and acidic types a NE trend. Nearby is an eroded volcanic vent from which olivine gabbro has been collected.
3)
TheRadfan Mountains are marginal to the volcanic province and are partly built of the Cretaceous Tawila Sandstone Group, the interest being in a WNW dyke swarm of non-olivine basalt and dolerite.
TL;DR: In this article, the authors present a bref historique sur l'emploi des different methodes geophysiques for the recherche des forces endogenes en Italy.
Abstract: L’auter fait tout d’abord un bref historique sur l’emploi des differentes methodes geophysiques pour la recherche des forces endogenes en Italie. La prospection geothermique (etude de la repartition des T° et gradients de T°) apparut paradoxalement assez tardivement et fut experimentee d’abord a faible profondeur (moins de 2 m). En 1960 sur la demande de la Societe Larderello les techniciens de la C.M.P. executerent pour la premiere fois dans la zone de Larderello des mesures systematiques a profondeur plus elevee (une trentaine de metres). Devant les resultats favorables obtenus, ce type de prospection fut ensuite etendu a la region du Monte Amiata sur une surface de 500 km2 et a toute la region de Larderello sur une surface de 1800 km2. L»suteur expose brievement la technique utilisee dans les mesures du gradient de temperature et presente les eartes obtenues. La mise en evidence d’une serie d’anomalies a plus de 2°/10 m sur le Monte Amiata a permis de delimiter le champ productif de Piancastagnaio et de decouvrir celui de Poggio Nibbio. A Larderello la carte des gradients a montre que la courbe 2°/10 m englobe les zones d’exploitation et qu’il n’existe pas d’autres champs en dehors de ceux actuellement en production; seules quelques apophyses des champs connus peuvent encore faire l’objet d’une nouvelle exploitation. L’anomalie regionale du gradient (superieure a 0,50°/10 m) couvre une surface superieure a 200 km2 sur le Monte Amiata et a 1200 km2 a Larderello. La prospection electrique du Monte Amiata a permis de dessiner l’allure structurale des calcaires, qui sont le magasin des fluides chauds, sous leur converture argileuse, mettant en evidence deux systemes d’accidents de direction NE-SO et NO-SE. Ces accidents limitent plusieurs structures relevees dont certaines correspondent aux anomalies thermiques. L’ordre de grandeur de la temperature au toit des calcaires a pu etre fixe par comparaison des donnees structurales et thermiques. L’allure du mur de la couverture volcanique a egalement ete determinee et l’on a pu constater une coincidence entre certains accidents NO-SE au mur du volcanique et les accidents au toit des calcaires. Enfin il est apparu que les champs geothermiques correspondent a une anomalie regionale negative de la gravite qui contraste avec les structures relevees des calcaires au droit de ces champs. Cette anomalie est certainment d’origine profonde et pourrait etre en relation avec la presence d’une racine sialique.
TL;DR: In this paper, the authors summarized the geochemical and petrogenetic aspects of an investigation of late Tertiary to Recent volcanic rocks in the Amboseli area of southern Kenya.
Abstract: The paper summarizes the geochemical and petrogenetic aspects of an investigation of late Tertiary to Recent volcanic rocks in the Amboseli area of southern Kenya.
TL;DR: The performance of Old Faithful has been remarkably stable for the past 100 years as mentioned in this paper, and the principle change has been the gradual developmnt of a bimodal character to the frequency distribution curve for the intervals between eruptions.
Abstract: The performance of Old Faithful has been remarkably stable for the past 100 years. Rainfall and earthquakes have had little influence on its eruption cycle, although the Hebgen Lake Earthquake of 1959 caused a sudden lengthening of the long interval between eruptions. The principle change has been the gradual developmnt of a bimodal character to the frequency distribution curve for the intervals between eruptions.
TL;DR: In this article, the results of heat flow studies made in different parts of India including Kolar Gold Field, Cuddapah basin, Singhbhum thrust zone, Aravalli mountain system of Precambrian age, Godavary valley of Mesozoic age and Cambay basin of Cenozoic ages are discussed.
Abstract: Results of heat flow studies made in different parts of India including Kolar Gold Field, Cuddapah basin, Singhbhum thrust zone, Aravalli mountain system of Precambrian age, Godavary valley of Mesozoic age and Cambay basin of Cenozoic age are discussed. Heat flow has been found to be low in the southern part of the Preambrian shield. Relatively higher values have been obtained along the northeastern (Singhbhum) and the northwestern parts of the shield (Aravallies). High heat flow has been found along the southeastern part of the Godavary valley and the Cambay basin. The correlation of heat flow with geology and tectonic history in the respective areas is discussed.
TL;DR: In this article, Rittmann demontre que le " ns" (sodasilite) est du au transport gazeux de substances pneumatophiles provenantes d'un magma basaltique alcalin and cedees au magma anatectique au contact.
Abstract: L’exces de sodium dans les hyalopantellerites pose un probleme pas encore resolu definitivement malgre les efforts d’eminents specialistes. A l’aide d’une serie de nouvelles analyses de differents echantillons d’une meme coulee, l’auteur, en accord avec les vues deA. Rittmann, demontre que le « ns » (sodasilite) est du au transport gazeux de substances pneumatophiles provenantes d’un magma basaltique alcalin et cedees au magma anatectique au contact. Pendant la crystallisation, le « ns » reste dans le bain residuel et s’accumule en etat disperse moleculairement dans la croute vitreuse des coulees sodarhyolitiques, denominee « hyalopantellerites » parH. S. Washington.
TL;DR: The Permian volcanic deposits col'ering an extensive area southeast of Lake Singkarak, Central Sumalra, have been mapped in detail and studied in relation to the structural development of the pre-Tertiary Sumatra orogene.
Abstract: The Permian volcanic deposits col'ering an extensive area southeast of Lake Singkarak, Central Sumalra, have been mapped in detail and studied in relation to the structural development of the pre-Tertiary Sumatra orogene. During the Permian time, Central Sumatra was occupied by aa elongated sea basin in which thick sequences of bathyal and neritic sediments were deposited. Pelitic sediments dominated, but at the same time volcanic activity started in this area. The volcanic products comprise mainly ftows of hornblende and augite andesites whit their tuffs. In some parts of southern sumatra the volcanic activity lasted till cretaceous ume. The main phase of foiding took place about 120 m'y. ago accompanied by an emplacement of granitic rocks. After an uplift in younger Cretaceous time, the area was strongly attacked by erosion. The regional geologic history of Sumatra revealed clearly a divergent behaviour from the classical concept of magmatic evolution in an orogenic belt as demonstrated by the dominantly andesitic charebter of the geosynlinal volcanism Other examples of volcanism associated with geosynclinal subsidence, possessing an andesitic rather than a basaltic character. could also be observed in the Tertiary Sunda mountain system of Sumatra. The Indonesian examples and similar occurrences of andesitic volcanism during a geo-sysnclinal subsidence in other parts of the world, show that much work still will have to be done in order to gain a better understanding regarding the relationship between volcanism and orogenesis.
TL;DR: The petrological and geochemical aspects of the ultramafic and basic plutonic rocks of Betancuria Massif are examined in this paper, where wehrlite, pyroxenite, olivine-gabbro and gabbro formed by magnesium-rich olivines, clinopyroxene and plagioclase.
Abstract: The petrological and geochemical aspects of the ultramafic and basic plutonic rocks of Betancuria Massif are examined. The rocks consist of gradational varieties of wehrlite, pyroxenite, olivine-gabbro and gabbro formed mainly by magnesium-rich olivine, clinopyroxene and plagioclase. The Complex exhibits structures and textures characteristic of layered igneous rocks;i.e., banding, layering, lamination, etc...; rocks are therefore considered as cumulates or magmatic sediments.
TL;DR: The Star Mountain rhyolite as discussed by the authors is the largest known rhyolitic mass to have been emplaced as a liquid flow rather than as a '' froth flow'' or nuee ardente.
Abstract: The Star Mountain rhyolite covers 500 square miles in the Davis Mountains, 100 miles east of El Paso, Texas. It appears to be the largest known rhyolitic mass to have been emplaced as a liquid flow rather than as a « froth flow » or nuee ardente. That it was emplaced as a liquid is shown by the lineation of phenocrysts, the vesicular and autobrecciated zones, baking of underlying tuffs, and by the complete absence of shard structures and evidence for welding. Three flow units with an aggregate thickness of 800 feet can be distinguished on the basis of field, chemical, and petrographic criteria. With the exception of some vesicular zones the rock is either finely crystalline and massive, or glassy and brecciated. Minor structures indicate that the flow of each unit was highly irregular.
Enel1
TL;DR: In this paper, Enel avait traces for le developpement des ressources endogenes sur le territoire italien, on avait inclu des etudes geologiques, des prospections geochimiques et geophysiques ayant le but de completer la recherche geothermique dans la region du Monte Amiata (Toscane).
Abstract: Dans le cadre des programmes que l’ENEL avait traces pour le developpement des ressources endogenes sur le territoire italien, on avait inclu des etudes geologiques, des prospections geochimiques et geophysiques ayant le but de completer la recherche geothermique dans la region du Monte Amiata (Toscane).