A Tale of Two Reservoirs: Kı̄lauea’s April-May 2015 Events

Abstract:

The existence of multiple magma reservoirs beneath Kı̄lauea’s summit area is well known, but in May 2015, we had the unique opportunity to observe an instance of rapid magma exchange between reservoirs.

The series of events began on April 22, with rapid inflation of the shallow (~1.5 km below the surface) reservoir near Halema‘uma‘u (HMM) Crater in Kı̄lauea Caldera. Inflation continued, at an exponentially decaying rate, for more than a week, while the lava lake within the vent in HMM rose about 40 m, overtopping its rim and spilling onto the crater floor. Inflation was accompanied by elevated seismicity in the caldera and especially in the upper East Rift Zone (UERZ). For a little more than a week after deformation rates slowed, the lava lake put on a spectacular show for hordes of appreciative onlookers, while intense seismicity kept Hawaiian Volcano Observatory staff on alert. On May 11, borehole tiltmeters began recording rapid deflation of the HMM reservoir, as lake level began to drop and earthquakes in the south caldera increased in rate and magnitude. Within a day, inflation in the south caldera was clear from tilt, GPS and InSAR data. The visual pattern of deformation and simple inverse modeling are consistent with the south caldera magma reservoir—a complex feature often imaged in the past, especially by leveling and InSAR—as the main source of this deformation. Inflation in the south caldera proceeded at an exponentially increasing rate for about 5 days. During this time, the lava lake level continued to drop to about 20 m below pre-April 22 levels, and seismicity in the UERZ waned. Our preliminary modeling suggests that the volume lost from the HMM reservoir and lava lake is comparable to that gained in the south caldera.

This event provides a rare glimpse of rapid magma transfer between two subcaldera magma storage bodies, raising new questions about how these reservoirs are connected and offering the potential to further elucidate the geometry of Kilauea’s summit magma storage system.