142 research outputs found
The viscosity of magmatic silicate liquids: A model for calculation
A simple model has been designed to allow reasonably accurate calculations of viscosity as a function of temperature and composition. The problem of predicting viscosities of anhydrous silicate liquids has been investigated since such viscosity numbers are applicable to many extrusive melts and to nearly dry magmatic liquids in general. The fluidizing action of water dissolved in silicate melts is well recognized and it is now possible to predict the effect of water content on viscosity in a semiquantitative way. Water was not incorporated directly into the model. Viscosities of anhydrous compositions were calculated, and, where necessary, the effect of added water and estimated. The model can be easily modified to incorporate the effect of water whenever sufficient additional data are accumulated
Carbon isotope study on Celtic graphite-tempered archaeological ceramics from the South Transdanubian region (Hungary)
Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean
Author Posting. © Nature Publishing Group, 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 453 (2008): 1236-1238, doi:10.1038/nature07075.Roughly 60% of the Earthâs outer surface is comprised of oceanic crust formed by volcanic
processes at mid-ocean ridges (MORs). Although only a small fraction of this vast volcanic
terrain has been visually surveyed and/or sampled, the available evidence suggests that
explosive eruptions are rare on MORs, particularly at depths below the critical point for
steam (3000 m). A pyroclastic deposit has never been observed on the seafloor below 3000
m, presumably because the volatile content of mid-ocean ridge basalts is generally too low
to produce the gas fractions required to fragment a magma at such high hydrostatic
pressure. We employed new deep submergence technologies during an International Polar
Year expedition to the Gakkel Ridge in the Arctic Basin at 85°E, to acquire the first-ever
photographic images of âzero-ageâ volcanic terrain on this remote, ice-covered MOR. Our
imagery reveals that the axial valley at 4000 m water depth is blanketed with
unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele),
covering a large area greater than 10 km2. At least 13.5 wt% CO2 is required to fragment
magma at these depths, which is ~10x greater than the highest values measured to-date in
a MOR basalt. These observations raise important questions regarding the accumulation
and discharge of magmatic volatiles at ultra-slow spreading rates on the Gakkel Ridge (6-
14 mm yr-1, full-rate), and demonstrate that large-scale pyroclastic activity is possible
along even the deepest portions of the global MOR volcanic system.This research was
funded by the National Aeronautics and Space Administration, the National Science Foundation,
and the Woods Hole Oceanographic Institution
Fluidal pyroclasts reveal the intensity of peralkaline rhyolite pumice cone eruptions
This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present and future) through which several of the authors are supported. In addition, Clarke was funded by a NERC doctoral training partnership grant (NE/L002558/1).Peralkaline rhyolites are medium to low viscosity, volatile-rich magmas typically associated with rift zones and extensional settings. The dynamics of peralkaline rhyolite eruptions remain elusive with no direct observations recorded, significantly hindering the assessment of hazard and risk. Here we describe uniquely-preserved, fluidal-shaped pyroclasts found within pumice cone deposits at Aluto, a peralkaline rhyolite caldera in the Main Ethiopian Rift. We use a combination of field-observations, geochemistry, X-ray computed microtomography (XCT) and thermal-modelling to investigate how these pyroclasts are formed. We find that they deform during flight and, depending on size, quench prior to deposition or continue to inflate then quench in-situ. These findings reveal important characteristics of the eruptions that gave rise to them: that despite the relatively low viscosity of these magmas, and similarities to basaltic scoria-cone deposits, moderate to intense, unstable, eruption columns are developed; meaning that such eruptions can generate extensive tephra-fall and pyroclastic density currents.Publisher PDFPeer reviewe
Toward the fabrication of extruded microstructured bioresorbable phosphate glass optical fibers
Reply [to âComment on âOxygen isotope partitioning among the minerals in igneous and metamorphic rocksââ]
THE MIXING PROPERTIES OF MELTS AND GLASSES IN THE SYSTEM NAALSI3O8-KALSI3O8 - COMPARISON OF EXPERIMENTAL-DATA OBTAINED BY KNUDSEN CELL MASS-SPECTROMETRY AND SOLUTION CALORIMETRY
The apparent differences between heats of mixing determined by solution calorimetric measurements on quenched samples in the system NaAlSi3O8-KAlSi3O8 and heats of mixing determined at high temperatures by Knudsen cell mass spectrometry are caused by thermal effects related to the glass transition. When these effects are allowed for, the calorimetric data and Knudsen cell measurements are in good agreement. © 1985
Thermodynamic Analysis of Quartz and Cristobalite Solubilities in Water at Saturation Vapor Pressure
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