On the interpretation of gravity variations in the presence of active hydrothermal systems: Insights from the Nisyros Caldera, Greece

Gottsmann, Joachim; Rymer, Hazel; Wooller, Luke

doi:10.1029/2005gl024061

Cited by 24 publications

(23 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Nisyros has shown some signs of activity over the last decades, and a moderate-size explosive eruption could happen anytime (Lagios et al 2005;Papadopoulos et al 1998). Hydrothermal explosions also pose a serious threat due to unstable degassing processes (Gottsmann et al 2005(Gottsmann et al , 2007.…”

Section: Discussionmentioning

confidence: 99%

Characterization of tephra deposits with limited exposure: the example of the two largest explosive eruptions at Nisyros volcano (Greece)

et al. 2011

View full text Add to dashboard Cite

Explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize. In fact, the determination of physical parameters such as column height, mass eruption rate, erupted volume, and eruption duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected. We have applied and compared different modeling approaches for the characterization of the two main tephra deposits, the Lower Pumice(LP) and Upper Pumice (UP) of Nisyros volcano, Greece, which are exposed only within 5 km of the probable vent. Isopach and isopleth maps were compiled for two possible vent locations (on the north and on the south rim of the caldera), and different models were applied to calculate the column height, the erupted volume, and the mass eruption rate. We found a column height of about 15 km above sea level and a mass eruption rate of about 2×10^7 kg/s for both eruptions regardless of the vent location considered. In contrast, the associated wind velocity for both UP and LP varied between 0 and 20 m/s for the north and south vent, respectively. The derived erupted volume for the south vent (considered as the best vent location) ranges between 2 and 27×10^8 m3 for the LP and between 1 and 5×10^8 m3 for the UP based on the application of four different methods (integration of exponential fit based on one isopach line, integration of exponential and power-law fit based on two isopach lines, and an inversion technique combined with an advection–diffusion model). The eruption that produced the UP could be classified as subplinian. Discrepancies associated with different vent locations are smaller than the discrepancies associated with the use of different models for the determination of erupted mass, plume height, and mass eruption rate. Proximal outcrops are predominantly coarse grained with ≥90 wt% of the clasts ranging between −6phi and 0phi. Theassociated total grainsize distribution is considered to result from a combination of turbulent fallout from both the plume margins and the umbrella region, and as a result, it is fines-depleted. Given that primary deposit thickness observed on Nisyros for both LP and UP is between 1 and 8 m, if an event of similar scale were to happen again, it would have a significant impact on the entire island with major damage to infrastructure, agriculture, and tourism. Neighboring islands and the continent could also be significantly affected

show abstract

Section: Discussionmentioning

confidence: 99%

Characterization of tephra deposits with limited exposure: the example of the two largest explosive eruptions at Nisyros volcano (Greece)

et al. 2011

View full text Add to dashboard Cite

show abstract

“…The source parameters ͑size, position, amount and density of the redistributed mass, etc.͒ are then retrieved by fitting observed and calculated data through an appropriate inversion scheme. Many studies have proved that this approach can supply unique insights into the processes that lead to unrest ͑e.g., Battaglia et al, 2003b;Berrino, 1994;Bonafede and Mazzanti, 1998;Branca et al, 2003;Charco et al, 2007c;Currenti et al, 2007;Eggers, 1987;Fernández et al, 2001b;Furuya et al, 2003b;Gottsmann et al, 2005;Jachens and Roberts, 1985;Jousset and Okada, 1999;Okubo et al, 1991;and Rymer, 1994͒. Major shortcomings of this approach are that the wrong model might be used to fit the observed data because different elastic models can produce similar effects, and that the simplifications ͑e.g., the assumption that the crust is a homogenous, isotropic, elastic medium͒ that make analytical models tractable can yield misleading volcanological interpretations.…”

Section: Discussionmentioning

confidence: 99%

4D volcano gravimetry

Gottsmann²,

et al. 2008

View full text Add to dashboard Cite

Time-dependent gravimetric measurements can detect subsurface processes long before magma flow leads to earthquakes or other eruption precursors. The ability of gravity measurements to detect subsurface mass flow is greatly enhanced if gravity measurements are analyzed and modeled with ground-deformation data. Obtaining the maximum information from microgravity studies requires careful evaluation of the layout of network benchmarks, the gravity environmental signal, and the coupling between gravity changes and crustal deformation. When changes in the system under study are fast ͑hours to weeks͒, as in hydrothermal systems and restless volcanoes, continuous gravity observations at selected sites can help to capture many details of the dynamics of the intrusive sources. Despite the instrumental effects, mainly caused by atmospheric temperature, results from monitoring at Mt. Etna volcano show that continuous measurements are a powerful tool for monitoring and studying volcanoes.Several analytical and numerical mathematical models can beused to fit gravity and deformation data. Analytical models offer a closed-form description of the volcanic source. In principle, this allows one to readily infer the relative importance of the source parameters. In active volcanic sites such as Long Valley caldera ͑California, U.S.A.͒ and Campi Flegrei ͑Italy͒, careful use of analytical models and high-quality data sets has produced good results. However, the simplifications that make analytical models tractable might result in misleading volcanological interpretations, particularly when the real crust surrounding the source is far from the homogeneous/isotropic assumption. Using numerical models allows consideration of more realistic descriptions of the sources and of the crust where they are located ͑e.g., vertical and lateral mechanical discontinuities, complex source geometries, and topography͒. Applications at Teide volcano ͑Tenerife͒ and Campi Flegrei demonstrate the importance of this more realistic description in gravity calculations.

show abstract

“…Two preliminary data sets ͑corrected for Earth tide, ocean loading, instrument drift, atmospheric pressure, and temperature variations͒ collected in 2006 and 2007 showed periodic changes on the order of 60-90 Gal over approximately 26 hours. This raises the possibility that discrete 4D gravity surveys can be significantly affected by the time at which a given measurement is made because these short-term changes are of the same magnitude as those observed in our annual surveys ͑Williams- Gottsmann et al, 2005͒. However, the lack of a secondary meter to constrain nonvolcanic signals currently limits unambiguous interpretations.…”

Section: Masaya Volcano Nicaraguamentioning

confidence: 73%

Toward continuous 4D microgravity monitoring of volcanoes

et al. 2008

View full text Add to dashboard Cite

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 months͒ have shown enticing evidence of very rapid changes in the volcanic plumbing system ͑minutes to hours͒ 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.

show abstract

On the interpretation of gravity variations in the presence of active hydrothermal systems: Insights from the Nisyros Caldera, Greece

Cited by 24 publications

References 16 publications

Characterization of tephra deposits with limited exposure: the example of the two largest explosive eruptions at Nisyros volcano (Greece)

Characterization of tephra deposits with limited exposure: the example of the two largest explosive eruptions at Nisyros volcano (Greece)

4D volcano gravimetry

Toward continuous 4D microgravity monitoring of volcanoes

Contact Info

Product

Resources

About