Showing papers by "University of Iceland published in 1977"

Current rifting episode in north Iceland

Abstract: A major rifting episode is now occurring in north Iceland. This started on 20 December 1975, with a basaltic eruption, an exceptionally intense earthquake swarm and movement on an 80-km segment of the plate boundary. Inflation and deflation of the Krafla caldera indicate upwelling of magma and injection into the rift zone. Historical records show that similar episodic rifting occurs in this region every 100–150 yr.

Extension of the geomagnetic polarity time scale to 6.5 m.y.: K-Ar dating, geological and paleomagnetic study of a 3,500-m lava succession in western Iceland

Abstract: More than 400 successive lavas in Borgarfjordur, western Iceland, have been subjected to paleomagnetic and K-Ar age analysis. Volcanism in the region was virtually continuous between about 7.0 and 2 m.y. ago, during which time more than 3,500 m of volcanics and interbedded sediments accumulated. Regression analysis of the K-Ar age and aggregate thickness data demonstrates that the rate of growth of the lava pile was remarkably uniform at 730 m/m.y. throughout the whole period. The magnetostratigraphic and K-Ar data indicate a nearly complete record of the geomagnetic polarity history and extend the polarity time scale based upon data from subaerial volcanic rocks to about 6.5 m.y. ago. The boundaries of polarity epoch 5 are shown to be 5.34 and 5.83 m.y. Epoch 6 lies between about 6.54 and 5.83 m.y. ago, during which time three normal polarity events are recognized. The ages determined for the polarity-interval boundaries in this study confirm recent estimates derived from analyses of marine magnetic anomalies using sea-floor–spreading assumptions. The results show that it is possible to obtain reliable K-Ar ages on lavas that have undergone zeolite facies metamorphism at temperatures up to about 150°C by careful selection of samples that are well crystallized and have their original high-temperature mineralogy preserved. A revised estimate of 5.2 ± 0.1 m.y. is proposed for the age of the Miocene-Pliocene boundary.

Hot Groundwater Systems in Iceland Traced by Deuterium: Paper presented at the Nordic Hydrological Conference (Reykjavik, Iceland, Aug-Sep, 1976)

Abstract: This paper summarizes the result obtained for hydrothermal systems in Iceland, by using deuterium and oxygen-18 as natural tracers. The deuterium content of a single sample of a local cold spring or river, except those rivers fed by considerable amount of glacier melt water, can be used to estimate the mean deuterium concentration of precipitation in the corresponding locality. Furthermore the deuterium content of the last winter layer, collected on Icelandic glaciers in spring before the melting season, is practically identical to the mean value of the corresponding annual precipitation. These facts have been used to draw a detailed map showing the amount of deuterium in precipitation over the whole country. Deep ice core studies show that the deuterium content of precipitation in each place has remained more or less unchanged during the last 8000 years. Measurements of both deuterium and oxygen-18 in the groundwater have confirmed that all groundwater in Iceland is originally meteoric and that the deuterium content of the thermal water does not change on its way through the bed-rock. The deuterium content of water discharging from hot springs or drill holes is often very different from the deuterium content of local precipitation. On the other hand, by comparing results obtained with the deuterium map, it is often possible to find where this water has fallen as rain and to trace its underground flow path. Deuterium measurements have been made on water from nearly all geothermal areas in the country. The results are drawn up together in one picture, which shows the origin and flow paths of most of the hot groundwater systems in Iceland. Finally it has been possible to give som idea of the age of the thermal groundwater, i.e. the time past since precipitation. The thermal water is obviously of varying ages. The »youngest« water seems only to be a few decades old, whereas the »oldest« appears to be from the last glaciations.

Prevalence of hypodontia and malformations of permanent teeth in Iceland

Abstract: This study was performed to elucidate the prevalence of hypodontia and congenital malformations of permanent teeth in Iceland. Computer analysis was done on the basis of results from examining 1,116 children (521 boys and 595 girls), or about 9.5 % of all schoolchildren in Reykjavik in stages DS 3 (canines and premolars erupting) and DS 4 (canines and premolars fully erupted) of dental development at the time of the study. The age range was mainly from 8–16 years. The prevalence of congenitally missing teeth (second and third molars excluded) was 6.7 % in boys and somewhat higher, 8.9 %, in girls, 7.9 % for both sexes combined. On the average, each child was missing 1.9 teeth. In the girls, the most commonly absent teeth were the mandibular second premolar (55 %), the maxillary second premolar (19 %), and the maxillary lateral incisors (18 %). In the boys the figures were 51 %, 18% and 10%, respectively. Malformation of permanent teeth, mainly in the form of pegshaped maxillary laterals, was also less common in the boys, 1.3 % against 3.0 % in the girls, and 2.2 % for both sexes combined. Among Icelandic children hypodontia and/or congenital malformation of permanent teeth were found in 9.1 %.

Upper Miocene and Pliocene geomagnetic secular variation in the Borgarfjordur area of Western Iceland

Abstract: Summary. A total of 362 successive lava flows, which were extruded at a regular rate between t = 6.7 and 1.6 Myr in the Borgarfjordur area of Western Iceland, have been subjected to palaeomagnetic study. In contrast to the result of a study by Wilson & McElhinny of palaeomagnetic data from a long sequence of lava flows in Eastern Iceland, there does not exist any long-term increase of geomagnetic inclination in Western Iceland between t = 7 and 3 Myr which, as they show, would produce a change in the distance to the associated virtual geomagnetic poles (VGP’s) from greater than the geographic co-latitude to less than the co-latitude (or, with respect to the site, from ‘far side’ of the geographic pole to ‘near-side’ of the .geographic pole). Instead the geomagnetic inclination is less than that required for an axial dipole field, providing ‘far-side’ VGP positions for all data groups. The mean VGP positions are almost identical for four successive polarity epochs (two of reversed polarity, and two of normal polarity), consistent with reversal of the main dipole being accompanied by reversal of the nondipole field. SF, the angular standard deviation of groups of VGP positions, is used as an expression of palaeosecular variation of the magnetic field. It is shown to be almost constant throughout the 5-Myr period, suggesting that standing and drifting non-dipole fields have not combined to produce strong secular variation which is in principle possible in high latitudes. This conclusion is weakened by the suspicion that the conventional exclusion of data from lavas with low-latitude VGP positions has discriminated against the discovery of high palaeosecular variation rates.

The ultrastructure of early visna lesions.

Abstract: The ultrastructure of visna, a slowly progressive meningo-encephalomyelitis of sheep, was studied in animals sacrificed one month after intracerebral inoculation of visna virus. The major pathological changes, representative of those seen during the first year after infection, consist of inflammation and minor focal destructive lesions of grey and white matter. The inflammatory infiltrates, both subependymal and perivascular as well as of the choroid plexus, were composed mainly of lymphocytes and macrophages with varying numbers of plasma cells. The demyelination seen was of the secondary or Wallerian type. There was no evidence of primary demyelination. Visna virions were not seen in any of the CNS material studied. The ultrastructural findings are compatible with the view that lesions in visna may be induced by a cell-mediated immune response. However, changes characteristic of an autoimmune reaction to myelin antigens were not observed.

An epidemiologic study of dental space anomalies in Icelandic schoolchildren.

Abstract: This study was performed mainly to determine the prevalence of space anomalies with regard to the various stages of dental development in Icelandic schoolchildren. The sample consisted of 1,641 randomly selected children (791 boys and 850 girls), making up 9.5 % of the children attending all primary and secondary schools in Reykjavik during the school year 1972–73. In most of the frequencies of the different space anomalies boys showed a higher prevalence than girls. In both sexes there was often a significant difference from one stage of dental development to another. The results were compared with those reported for other ethnic groups.

A Prospective Comparative Study of Clinical and Histological Characteristics in Icelandic and Danish Patients with Gastric Ulcer, Duodenal Ulcer, and X-Ray Negative Dyspepsia: I. Design and Clinical Features

Abstract: Iceland (IS) and Denmark (DK) are ethnically, culturally, and economically closely related Nordic countries, but gastric cancer is much more frequent in Iceland, and other differences in the occurrence rates of gastric diseases are also suspected. Therefore a cooperative study was initiated comparing Icelandic and Danish patients with gastric ulcer (GU), duodenal ulcer (DU), and X-ray negative dyspepsia (XND) as regards clinical features, external factors of possible importance for gastritis and cancer, gastroscopic appearance, and histological gastric mucosal changes. The project lasted one year and comprised 93 Icelandic and 88 Danish patients. A large number of comparisons showed a high degree of similarity between Icelandic and Danish patients. Significant differences were found in tobacco consumption (DK > IS), duration of symptoms in XND (IS > DK), whereas the position ratio of GU (IS IS) showed non-significant trends. Significant difference was found...

The deflecting wrinkle on the teeth of Icelanders and the mongoloid dental complex.

Abstract: Three local populations from Northeast Iceland are surveyed for the occurrence of the deflecting wrinkle of the metaconid on second deciduous and first permanent lower molars. The trait occurs more frequently on dm2 than on M1, and no sexual dimorphism is found, as expected. However, the frequencies are clearly within those predicted by the Mongoloid dental complex for Mongoloid populations. It is therefore suggested that the inclusion of the deflecting wrinkle in the Mongoloid dental complex be re-evaluated, and the racial diagnostic value of the trait taken with reservation.

Confirmation of central volcanoes off the Icelandic coast

Abstract: THE Icelandic shelf and slope region occupies much of the transition zone between the complex Icelandic hot spot and more uniform ocean-ridge areas to the north and south. This transition zone is relatively little known geologically, but in this communication we summarise some recent observations on the nature of its basement. It is well known1 that the shelf is generally narrower off the eastern half of Iceland than off its western half. This is most obvious south of Iceland, where the shelf width changes suddenly at the eastern volcanic zone; the insular slope is also steepest off south-eastern and north-eastern Iceland. Recent geophysical surveys1,2 in the southern and south-eastern shelf area have indicated the presence of an abrupt basement scarp now covered by sediments, 5–14 km inside the bathymetric shelf break (Fig. 1). This scarp is at least 1 km high and only a few km in mean width. No such basement scarp is indicated in comparable surveys conducted so far off western Iceland1–3; north-east of the island, detailed data is not yet available.

Experimental Visna in Icelandic lambs.

Abstract: Icelandic lambs were inoculated intracerebrally with visna virus at 10 days of age and sacrificed 22–25 days after infection. Virus was isolated from all 5 inoculated animals, and pronounced periventricular lesions, typical of early visna, were seen in the 3 lambs with the most widespread infection. The response to the infection was very similar to that seen previously in adult Icelandic sheep. In addition, 2 uninoculated lambs housed with the injected animals and sacrificed at the same time also became infected.

At leve på en vulkan

Abstract: Thorarinsson, S.: At leve pa en vulkan. Geografisk Tidsskrift 76: 1–13. Kobenhavn, juni 1. 1977. Disasters during Icelands history caused by the four damaging factors of volcanic eruption, tephra, ...

Sequential file processing in fortran IV

Abstract: The standard I/O facility for sequential disk/tape file handling in a Fortran IV IBM 360/370 Disk Operating System environment has some marked shortcomings, the most serious of which is that blocking of records is not provided for. This paper describes SAMFOR4 (Sequential Access Method in Fortran IV), a set of Fortran callable subprograms and a file declaration facility that enables the Fortran programmer to access and create ‘standard’ sequential files. Thus inter language compatibility of files is obtained. A manyfold increase in effectiveness may also be achieved.