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  • 1
    Electronic Resource
    Electronic Resource
    Magma movements in Etna volcano associated with the major 1991–1993 lava eruption: evidence from gravity and deformation (1995)
    Springer
    Bulletin of volcanology 57 (1995), S. 451-461 
    Details
    ISSN: 1432-0819
    Keywords: Key words Microgravity ; Ground deformation ; Etna ; Eruption precursors ; Dyke injection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The 1991–1993 eruption was probably the largest on Mt. Etna for 300 years. Since then the volcano has entered an unusually quiescent period. A comprehensive record of gravity and ground deformation changes presented here bracket this eruption and give valuable insight into magma movements before, during and after the eruption. The gravity and deformation changes observed before the eruption (1990–1991) record the intrusion of magma into the summit feeder and the SSE-trending fracture system which had recently been active in 1978, 1979, 1983 and 1989, creating the feeder dyke for the 1991–1993 eruption. In the summit region gravity changes between 1992 and 1993 (spanning the end of the eruption) reflect the withdrawal of magma from the conduit followed more recently (1993–1994) by the re-filling of magma in the conduit up to pre-eruption levels. In contrast, in the vicinity of the fracture zone, gravity has remained at the 1991–1992 level, indicating that no withdrawal has occurred here. Rather, magma has solidified in the fracture system and sealed it such that the 1993–1994 increase in magma level in the conduit was not accompanied by further intrusion into the flanks. Mass calculations suggest that a volume of at least 107  m3 of magma has solidified within the southeastern flank of the volcano.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00300989
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  • 2
    Electronic Resource
    Electronic Resource
    Calibration shifts in a LaCoste-and-Romberg gravimeter: comparison with a Scintrex CG-3M (1999)
    Oxford BSL : Blackwell Science Ltd
    Geophysical prospecting 47 (1999), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The reliability and ruggedness of LaCoste-and-Romberg gravity meters has meant that their use has extended over recent years from gravity mapping to the investigation of small gravity changes (〉 10 μGal) with time. When using the instrument at the limit of its capability, limitations become apparent. Some instruments drift more than others and some are prone to excessive tares. However, with regular servicing these problems are minimized. Here we demonstrate clear evidence for calibration changes of the order of 1000 ppm for LaCoste-and-Romberg meter G513, which, for gravity differences of over 50 mGal, represents a highly significant induced error of over 50 μGal. Data collected over 15 years using nearly 4000 mGal of the 7000 mGal range of the instrument illustrates that long periods of stability may be interspersed with periods lasting several months while the calibration changes by up to 0.1%. This is comparable with the calibration drift of a new Scintrex CG-3M instrument, although the process causing the change may not be the same.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1999.00118.x
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  • 3
    Electronic Resource
    Electronic Resource
    A Contribution to Precision Microgravity Data Analysis Using Lacoste and Romberg Gravity Meters (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 97 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The precision quoted for published microgravity surveys varies widely. This paper attempts to quantify the sources of error on a single gravity difference measurement using LaCoste and Romberg instruments. A combination of external effects (Earth tides, noise), reader effects (technique and field practice) and instrumental effects (tares, thermal drift, calibration) are shown to produce a maximum (worst case) error, for a single reading, of approx. 23 μgal and a minimum (best case) error of approx. 7μgal. Single difference measurements have corresponding errors of approx. 33 and 10μgal, respectively. Evidence is presented to demonstrate the importance of thermal and mechanical tares which are best removed from field data by isolating step functions using repeat readings rather than by (always) assuming linear drift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb00503.x
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanisms of magma eruption and emplacement at Mt Etna between 1989 and 1992 (1993)
    [s.l.] : Nature Publishing Group
    Nature 361 (1993), S. 439-441 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] At a late stage during the explosive activity from the southeast crater (10 September-6 October 1989), two prominent fissures developed, one erupting to the northeast2 and the second, a non-erupting fissure, extending 7 km towards the south-southeast. Seismic3'4, soil gas emanations5, thermal ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/361439a0
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Global outlooks (1996)
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 684-684 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] FOR those of us who came to study Earth sciences during the 1980s, it is hard to imagine a time when the theory of 'plate tectonics' did not exist. It is perfectly appropriate to describe the development of the theory during the 1960s as the great Earth-science revolution. Before then, the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/383684b0
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  • 6
    Electronic Resource
    Electronic Resource
    Energy budget analysis for Poás crater lake: implications for predicting volcanic activity (1989)
    [s.l.] : Nature Publishing Group
    Nature 339 (1989), S. 370-373 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Figure 1 depicts a model of the sub-surface geological structure of Poas volcano derived mainly from extensive gravity surveys combined with inferences from surface geology8'9. A narrow cylindrical magma feeder pipe is thought to penetrate an ancient caldera structure, ~4km across, now filled with ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/339370a0
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  • 7
    Electronic Resource
    Electronic Resource
    Gravity changes as a precursor to volcanic eruption at Poás volcano, Costa Rica (1989)
    [s.l.] : Nature Publishing Group
    Nature 342 (1989), S. 902-905 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The last major eruption at Poas was in 1953, when phreatic activity culminated in the growth of a 30-m-high pyroclastic cone and the formation of an inner crater, both within the old summit crater. Since then, a hot crater lake has absorbed any fluctuations in heat output7 from the magma feeder ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/342902a0
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  • 8
    Electronic Resource
    Electronic Resource
    Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua (1998)
    Springer
    Bulletin of volcanology 59 (1998), S. 345-355 
    Details
    ISSN: 1432-0819
    Keywords: Key words Masaya ; Santiago ; Pit ; Structure ; Microgravity ; Magma ; Gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Persistent activity at Masaya Volcano, Nicaragua, is characterised by cycles of intense degassing, lava lake development and pit crater formation. It provides a useful site to study the processes which govern such activity, because of its easy accessibility and relatively short cycles (years to decades). An understanding of the present activity is important because Masaya is visited by large numbers of tourists, is located close to major cities and has produced voluminous lavas, plinian eruptions and ignimbrites in the recent past. We provide structural and geophysical data that characterise the "normal" present state of activity. These indicate that the ongoing degassing phase (1993 to present) was not caused by fresh magma intrusion. It was associated with shallow density changes within the active Santiago pit crater. The activity appears to be associated predominantly with shallow changes in the pit crater structure. More hazardous activity will occur only if there are significant departures from the present gravity, deformation and seismic signatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050196
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  • 9
    Electronic Resource
    Electronic Resource
    Gravity and elevation changes at Askja, Iceland (1993)
    Springer
    Bulletin of volcanology 55 (1993), S. 362-371 
    Details
    ISSN: 1432-0819
    Keywords: Microgravity ; Ground deformation ; Tilt ; Magma injection ; Caldera unrest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Ground tilt measurements demonstrate that Askja is in a state of unrest, and that in the period 1988–1991 a maximum 48±3 μrad tilt occurred down towards the centre of the caldera. This is consistent with 126 mm of deflation at the centre of the caldera with a 2.5–3.0 km depth to the source of deformation. The volume of the subsidence bowl is 6.2x106 m3. When combined with high precision microgravity measurements, the overall change in sub-surface mass may be quantified. After correction for the observed elevation change using the free air gradient of gravity measured for each station, the total decrease in mass is estimated to be less than 109 kg. A small residual ground inflation and net gravity increase in the southeastern part of the caldera may be caused by dyke intrusion in this region. The minimum dimensions of such an intrusion or complex of intrusions are 1 m width, up to 100 m deep and up to several hundred metres thick.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301147
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    Paper (German National Licenses)
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