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Rymer, H.
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Rymer, H.
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- PublicationRestrictedBalancing bulk gas accumulation and gas output before and during lava fountaining episodes at Mt. Etna(2015-12-10)
; ; ; ; ; ;Carbone, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Zuccarello, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Messina, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Scollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Rymer, H.; 3The Open University, Milton Keynes, UK; ; ; ; We focus on a sequence of 9 lava fountains from Etna that occurred in 2011, separated by intervals of 5 to 10 days. Continuous measurements allowed to discover the occurrence of gravity decreases before the onset of most fountaining episodes. We propose that the gravity changes are due to the pre-fountaining accumulation of a foam layer at shallow levels in the plumbing system of the volcano. Relying on the relationship between amount of gas trapped in the foam and amount of gas emitted during each episode, we develop a conceptual model of the mechanism controlling the passage from Strombolian to lava fountaining activity. Gas leakage from the foam layer during the late stages of its accumulation increases the gas volume fraction at upper levels, thus inducing a decrease of the magma-static pressure in the trapping zone and a further growth of the foam. This feedback mechanism eventually leads to the collapse of the foam layer and to the onset of lava fountaining. The possibility to detect the development of a foam layer at depth and to set quantitative constraints on the amount of trapped gas is important because of the implications for forecasting explosive eruptions and predicting their intensity.714 52 - PublicationRestrictedThe effect of inertial accelerations on the higher frequency components of the signal from spring gravimeters(2010-08)
; ; ; ; ; ;Carbone, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Zuccarello, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Saccorotti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Rymer, H.; The Open University, Department of Earth and Environmental Sciences, Walton Hall, Milton Keynes, MK7 6AA, UK ;Rapisarda, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; ; Experimental and theoretical studies have shown that, due to the magma/gas dynamics in the upper part of a volcano’s plumbing system, gravity changes can develop over periods between a few tens of seconds and several hours. The mass transport, implied by certain fast-evolving volcanic processes, also constitute the source mechanism of seismic waves with frequencies over the lower limit of the seismic band. These seismic waves could affect the measuring system of spring gravimeters, that are increasingly used as continuously running devices to monitor and study active volcanoes. As a consequence, under some circumstances, the signal from a continuously running spring gravimeter will be the combination of the gravity field component and the inertial acceleration component, the latter due to the ground motion. In such cases, the inertial acceleration must be separated from the gravity signal to assess the amount of mass redistributed during the studied process. To achieve this separation, the frequency response curve of the spring gravimeter to inertial accelerations must be calculated, since it is not supplied by manufacturers. In this paper, we present a method to retrieve the above curve, using simultaneous recordings during the transit of teleseismic waves, of a LaCoste & Romberg D gravimeter and a Nanometrics Trillium 40 broadband seismometer, whose frequency response curve to ground acceleration is known a-priori. The use of teleseismic waves is particularly useful for our purpose since teleseisms are not associated with a local mass redistribution; the gravimeter will thus be affected only by the ground motion, making the above calculation possible. Our results show that, because of the instrumental damping, the effect of the inertial acceleration is reduced in the output signal from the gravimeter to 0.5 and 0.1 of its original value, at frequencies between 0.02 and 0.07 Hz, respectively. The robustness of the calculated frequency response curve is proven using independent simultaneous signals from gravimeter and broadband seismometer.258 31 - PublicationRestrictedUnrest at the Campi Flegrei caldera (Italy): a critical evaluation of source parameters from geodetic data inversion(2006)
; ; ; ;Gottsmann, J.; Institute of Earth Sciences bJaume AlmeraQ, CSIC, Lluı´s Sole´ Sabarı´s s/n, Barcelona 08028, Spain ;Rymer, H.; Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom ;Berrino, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; We have analysed the deformation documented during unrest at the Campi Flegrei caldera, Italy, between 1981 and 2001. Via inverse modelling, we constrain the location, geometry and size of the source responsible for the continuing period of surface deformation.We present a critical re-evaluation of results from previously published models and for the first time invert post-1994 data to infer source parameters. Our evaluation is based on constraints from additional horizontal displacement data, mechanical properties of the country rocks, effects of volcanic surface loading and on other geophysical and geochemical observations. We invert leveling and tide-gauge data for a spherical point (Mogi-model) source, a penny-shaped crack and finally a prolate spheroid. Despite the good qualities of fit of both the Mogi-model and the penny-shaped source to the vertical displacement data, our critical evaluation of the implied source properties forces us to reject these models. We propose instead a vertical prolate spheroid located about 800 m East of Pozzuoli at a depth of 2.9 km (95% confidence bound 2.0 to 4.2 km) with an aspect ratio of 0.51 (95% bounds 0.37–0.69) as a more appropriate source model. This model best accounts for the criteria employed and the observed deformation between 1981 and 2001. Combined with results from the inversion of gravity change data (1982–1984) for the spheroidal source, we infer a hybrid nature of the source including both magmatic and hydrothermal components.178 29 - PublicationRestrictedToward continuous 4D microgravity monitoring of volcanoes(2008-12)
; ; ; ; ; ; ;Williams-Jones, G.; Simon Fraser University, Department of Earth Sciences, Burnaby,British Columbia, Canada ;Rymer, H.; The Open University, Department of Earth and Environmental Sciences, Volcano Dynamics Group, Walton Hall, Milton Keynes ;Mauri, G.; Simon Fraser University, Department of Earth Sciences, Burnaby,British Columbia, Canada ;Gottsmann, J.; University of Bristol, Department of Earth Sciences, Bristol, U. K. ;Poland, M.; Hawaiian Volcano Observatory, United States Geological Survey, Hawaii National Park, Hawaii, U.S.A. ;Carbone, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; ; ; Four-dimensional or time-lapse microgravity monitoring has been used effectively on volcanoes for decades to characterize the changes in subsurface volcanic systems. With measurements typically lasting from a few days to weeks and then repeated a year later, the spatial resolution of theses studies is often at the expense of temporal resolution and vice versa. Continuous gravity studies with one to two instruments operating for a short period of time (weeks to months) have shown enticing evidence of very rapid changes in the volcanic plumbing system (minutes to hours) and in one case precursory signals leading to eruptive activity were detected. The need for true multi-instrument networks is clear if we are to have both the temporal and spatial resolution needed for effective volcano monitoring. However, the high cost of these instruments is currently limiting the implementation of continuous microgravity networks. An interim approach to consider is the development of a collaborative network of researchers able to bring multiple instruments together at key volcanoes to investigate multitemporal physical changes in a few type volcanoes. However, to truly move forward, it is imperative that new low-cost instruments are developed to increase the number of instruments available at a single site. Only in this way can both the temporal and spatial integrity of monitoring be maintained. Integration of these instruments into a multiparameter network of continuously recording sensors is essential for effective volcano monitoring and hazard mitigation.287 29 - PublicationRestrictedNew geophysical insight into the dynamics of Stromboli volcano (Italy)(2012)
; ; ; ; ;Carbone, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Zuccarello, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Montalto, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Rymer, H.; The Open University, Department of Earth and Environmental Sciences, Walton Hall, Milton Keynes, MK7 6AA, UK; ; ; A 56-hour gravity sequence, recorded in the crater area of Stromboli volcano, is presented. Data were acquired during a period of “normal” strombolian activity. High-frequency gravity anomalies (up to 20 microGal; T = tens of seconds) are observed. Comparison with independent data reveals that these changes reflect the response of the gravimeter excited by seismic waves during strombolian explosions. Correlated changes in the energy distribution over time appear in the continuous wavelet transforms of gravity and RMS-tremor, but over different scales, corresponding to periods centered at about 50 and 25 minutes, for gravity and tremor, respectively. We infer that the rate of fresh magma supply to the shallow feeding system controls the energy distribution over time of the coupled components in gravity and RMS-tremor signals. In particular, the gravity signal (with an average amplitude of 1-2 microGal) could be induced by temporary accumulations, at shallow depth, of the volatiles discharged by quiescent degassing. Changes in the rate of explosions from the summit craters correlate with changes in the amplitude of the coupled gravity and volcanic tremor oscillations, implying that, even though the slug-genesis process behind the explosions occurs at deeper levels, it is also controlled by the rate of gas-rich magma supply from below. Negative gravity anomalies of about 20 microGal, over intervals of some hours, are also observed, separated by intervals of about 24 hours. They could be induced by increases in magma vescicularity in the uppermost part of the conduit plexus, a view supported by (i) changes in the time/space distribution of tremor amplitudes and (ii) increases in spattering activity from a summit vent, both occurring during the development of the negative gravity anomalies. The processes behind mild Strombolian explosions do not trigger measurable gravity changes. Nevertheless, the slug ascent before a major explosion could induce a precursory gravity signal.491 35