CONTINUOUS GRAVITY MONITORING OF PERSISTENTLY ACTIVE VOLCANOES: THE HURDLES AND POTENTIAL BENEFITS

Four-dimensional or time-lapse microgravity monitoring has been used effectively on volcanoes for decades to characterize the mass and/or density changes in subsurface volcanic systems. However, with measurements typically lasting from a few days to weeks and then repeated a year or more later, the spatial resolution of these studies is often at the expense of temporal resolution and vice versa. When used in conjunction with GPS networks and InSAR, it is nevertheless possible to more accurately model the precursory signals leading to changes in volcanic activity. Continuous gravity studies with one to two instruments operating for a short period of time (days to months) have recently shown enticing evidence of very rapid changes (minutes to hours) in the shallow volcanic plumbing system of Masaya and Kilauea volcanoes and in one case, at Mt Etna, precursory signals leading to eruptive activity were detected. The need for true multi-instrument gravity networks is clear if we are to have both the temporal and spatial resolution needed for effective volcano monitoring. However, the high cost and logistical difficulties of installing these instruments is currently limiting the implementation of continuous microgravity networks. Until new low-cost instruments are developed, an interim approach is the development of a collaborative network of researchers able to bring multiple instruments together at a few type volcanoes to investigate multitemporal physicochemical changes in their shallow plumbing systems.