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The geology and geophysics of Lake Tarawera, New Zealand: Implications for sublacustrine geothermal activity
No full textThe Okataina Volcanic Centre is a large caldera system in the Taupo Volcanic Zone, New Zealand, which includes the Haroharo caldera, where the geothermally active Lake Tarawera is located at its southwestern boundary. Here, we show the results of high-resolution bathymetric mapping of the lake floor combined with gravity, magnetic and heat-flow surveys carried out over the lake, constrained by geochemical sampling. Our combined data elucidate the detailed geometry of the SW structural margin of the Haroharo caldera bisecting Lake Tar-awera, and the relationship with the regional faults related with the Taupo Volcanic Zone rift.In this context, the spatial distribution of heat-flow in Lake Tarawera appears controlled by fluid-focusing permeable zones associated with the structural lineaments and by peripheral, gravity-driven circulation of meteoric water associated with cooling of highly permeable rhyolite domes around the lakeshore. The structural boundary of the Haroharo caldera provides first-order control of heat-flow in the lake, with WNW striking normal faults to a lesser degree. An estimated total conductive output of similar to 5.3 MW escaping through the floor of Lake Tarawera is refracted by the thick layer of sediments, providing an impermeable layer to the convection of fluids, which in turn diminishes heat output compared to other lakes in this region.Our results contribute to modelling of hydrothermal circulation at the Okataina Volcanic Centre, and when integrated with data from the other lakes and the terrestrial geothermal output, it will contribute to determine the global geothermal output at this caldera system. The relationships to eruptive history and structural setting are the key to modelling similar geothermal system of other silicic calderas worldwide
Discovery of active hydrothermal venting in Lake Taupo, New Zealand
No full textThe Horomatangi geothermal system of Lake Taupo, New Zealand, is a sub-lacustrine equivalent of subaerial
geothermal activity nearby in the Taupo Volcanic Zone (TVZ). The setting of this system is rare within the TVZ as it
is directly associated with an individual volcanic feature, that of the 1.8 ka Taupo eruption vent. Two distinct
hydrothermal vent areas, named Te Hoata and Te Pupu, have been discovered during dives with the submersible
Jago. Venting of gases was seen at both sites and hot water (up to 45‡C) discharges at the Te Pupu site. Dilute water
samples have concentrations of SO4, Cl, Na and SiO2 above ambient lake water values. Gas samples have
compositions similar to other TVZ geothermal systems. Gas geothermometers indicate the existence of a hightemperature
hydrothermal environment beneath the lake with reservoir temperatures in excess of 300‡C. Chimney
structures were found at the Te Pupu site. They are up to 30 cm tall and mineralized by an ‘epithermal’ suite of
elements, including S, Hg, As, Sb and Tl. The walls of the chimneys are largely composed of diatoms and strands of
silicified filamentous bacteria embedded in an amorphous silica groundmass. Bacterial mats are commonly associated
with the gas vents and also occur at two hot springs. Close to the vents, commonly perched on top of dead chimneys
and/or exposed outcrops, are dense assemblages of what are probably a new species of sponge of the genus
Heterorotula. The sponges host a notably diversified, associated invertebrate fauna and represent a previously unseen
biomass on the lake floor. The sponges appear to have bored into the mineralized chimneys
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Discovery of active hydrothermal venting in lake Taupo, New Zealand: results from the Jago submersible dives
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