Evolution of dike opening during the March 2011 Kamoamoa fissure eruption, Kilauea Volcano, Hawai'i

The 5-9 March 2011 Kamoamoa fissure eruption along the east rift zone of Kilauea Volcano, Hawai'i, followed months of pronounced inflation at Kilauea summit. We examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar (InSAR) data set in combination with continuous GPS data. We solve for distributed dike displacements using a whole Kilauea model with dilating rift zones and possibly a deep decollement. Modeled surface dike opening increased from nearly 1.5 m to over 2.8 m from the first day to the end of the eruption, in agreement with field observations of surface fracturing. Surface dike opening ceased following the eruption, but subsurface opening in the dike continued into May 2011. Dike volumes increased from 15, to 16, to 21 million cubic meters (MCM) after the first day, eruption end, and 2 months following, respectively. Dike shape is distinctive, with a main limb plunging from the surface to 2-3 km depth in the up-rift direction toward Kilauea's summit, and a lesser projection extending in the down-rift direction toward Pu'u 'O'o at 2 km depth. Volume losses beneath Kilauea summit (1.7 MCM) and Pu'u 'O'o (5.6 MCM) crater, relative to dike plus erupted volume (18.3 MCM), yield a dike to source volume ratio of 2.5 that is in the range expected for compressible magma without requiring additional sources. Inflation of Kilauea's summit in the months before the March 2011 eruption suggests that the Kamoamoa eruption resulted from overpressure of the volcano's magmatic system.