On endogenous and exogenous factors controlling the behaviour of the Lusi eruption (Java, Indonesia)

The Lusi eruption started on Java Island on the 29^th of May 2006, almost two days after a M6.5 earthquake struck Yogyakarta. More than 16 years later, Lusi is still erupting clasts, mud, oil, and surges of thermogenic methane and mantle-derived CO₂. Lusi features a geysering behaviour, and its flow rate currently averages 50.000 m³/day with peaking up to 180.000 m³/day during the early phases of the eruption. Previous investigations revealed that at 4.5 km depth, Lusi is connected with the neighbouring volcanic complex that is fueling the eruption site. Observations also show that since 2006, Lusi’s behaviour has been periodically perturbed by seismic events and possibly by neighbouring volcanic eruptions. However, it remains unclear if/how other factors may influence Lusi’s eruptive behaviour. We use a statistical approach comparing flow rate records against a multiparametric database accounting for peak ground velocities and accelerations, tidal phases, Pressure and Temperature atmospheric variations, Geodetic monitoring (subsidence and inflation of the edifice), and faulting. A preliminary investigation of the relationship between daily flow rate and peak ground motion imposed by regional and teleseismic earthquakes shows that large amplitude seismic waves are often associated with increasing the flow rate at Lusi. Results can be fit by a power law. Geodetic monitoring shows a sudden increase in subsidence following major ground accelerations imposed by nearby seismic events and eruptions of neighbouring volcanic systems. Similarly, these events are also consistent with fresh extended fractures around Lusi and/or major breaching and deformations of the tall embankment walls surrounding the eruption site. When considering daily variations and using a higher resolution catalogue accounting for the fluid temperature of Lusi, we find that external factors such as local P/T and tidal events can alter the local temperature of the fluids emitted at the Lusi site.

Our results reveal that multiparameter monitoring represents a valuable approach to understanding the dynamics controlling the activity and the evolution of active eruption sites. Results could be useful in identifying potential precursors.