Toward continuous 4D microgravity monitoring of volcanoes

Abstract

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.

4D volcano gravimetry

“…Using continuous gravity measurements helps to overcome these drawbacks and reduces the exposure of personnel in active areas during paroxysmal ͑potentially dangerous͒ activity. ͑See also Williams-Jones et al, 2008.͒ For attaining appropriate precision with continuously running gravimeters, an ideal site is easily accessible ͑for checking the instrumentation frequently͒ and has small microseismic disturbance and very small temperature and pressure variations ͑Torge, 1989͒. Nevertheless, on an active volcano, the instruments are placed where there is the greatest chance of detecting meaningful gravity changes, which might only be close to an active crater ͑Branca et al, Carbone et al, 2008͒.…”

Insights into shallow magmatic processes at Kīlauea Volcano, Hawaiʻi, from a multiyear continuous gravity time series

“…Unfortunately, continuous gravity monitoring is a considerable challenge. First, gravimeters are expensive, so permanent deployments at volcanoes are relatively few in number [ Williams‐Jones et al ., ]. Continuous gravity has been used to track changes in volcanic activity at only a few sites, most notably Merapi (Indonesia) [ Jousset et al ., ], Etna [ Carbone et al ., ], and Kīlauea [ Carbone and Poland , ]; instruments have also been deployed at Vesuvius (Italy) [ Berrino et al ., ], and Soufrière Hills Volcano (Montserrat) [ Hautmann et al ., ], and have been used to study hydrothermal activity at Nisyros (Greece) [ Gottsmann et al ., ].…”

Monitoring the volcanic unrest of El Hierro (Canary Islands) before the onset of the 2011–2012 submarine eruption

“…The geochemical analysis of gases released by the ascending magma can be also useful to forecast a possible eruption [ Tedesco , 1995]. Many other techniques have been tested in the last decades as potential monitoring tools, like gravimetry [ Carbone et al , 2007; Williams‐Jones et al , 2008] or geomagnetism [ Zlotnicki and Le Mouel , 1988; Zlotnicki , 1995], both able to provide information about magma migration.…”