Did Excessive Rainfall Contribute to the Onset of the 2018 Kīlauea Activity?

On 3 May 2018, a fissure eruption marked the onset of the 62^nd episode of the current east rift zone eruption of Kīlauea (HI, USA). Prior to this, pronounced inflation was observed between Nov 2014 and June 2017 at the summit of Kīlauea ( 120 mm yr^-1: a strong indicator of dyke intrusion). However, between July 2017 and May 2018, the inflation rate at the summit decreased markedly ( 20 mm yr^-1), suggesting that the upwelling of magma had slowed somewhat.

For an intruding dyke to reach the surface and manifest as an eruption, a critical driving force must be maintained. Stalled intrusions can result from a reduction of this force (e.g. due to a reduction in magma flux) or by the dyke encountering a stratigraphic layer with contrasting mechanical properties. Similarly, a stalled or stalling intrusion can be reactivated by a reinvigoration of the upwelling magma pressure or by a local reduction in the effective stress around the dyke tip. These mechanisms have both been proposed to explain various intrusive events at Kīlauea.

Effective stress can decrease as a function of rainfall infiltration into the edifice and a consequent increase in interstitial pore pressure around the dyke tip. Intriguingly, the current episode of activity at Kīlauea was preceded by a highly anomalous rainfall pattern. NASA/JAXA Tropical Rainfall Measuring Mission and Global Precipitation Measurement mission data indicate that the period immediately preceding the onset of activity is the only timeframe where total rainfall exceeded the long-term average for 5 consecutive months.

Hydromechanical coupling is thought to contribute to many geological phenomena, including volcanic activity. Moreover, it has been previously shown that extreme rainfall may contribute to slip events in the fault system beneath Kīlauea (Cervelli et al., 2002). It is similarly possible that prolonged heavy rainfall through the first trimester of 2018 influenced effective stress around the dyke tip, facilitating or quickening its ascent to the surface. Diffusion models indicate that pressure changes on the order of MPa at a few km depth could result from recorded rainfall. We suggest that the anomalous rainfall leading up to the current fissure activity at Kīlauea was an important but hitherto overlooked contributing factor.