Using seafloor geodesy to monitor volcanic collapse on the south flank of Kilauea Volcano, Hawaii

A four-year seafloor geodetic study to measure vertical deformation on the submerged south flank of Kilauea volcano was conducted to monitor volcanic collapse oil the active Hilina slump. The Hilina slump is a hazardous feature that has been the site of significant deformation, major earthquakes with ground cracking and associated tsunami in the past and will likely be so in the future. Monitoring current deformation on the seafloor has extended the geodetic measurements on the volcano. Because the majority of Kilauea is submerged, offshore measurements are important. I describe the techniques used to collect and process the data and present the results of this first seafloor geodetic monitoring study on Kilauea.; A new technique was developed to collect campaign-style pressure sensor measurements on the seafloor in a geologically active area. Measurements were collected on three research cruises. The effects of density, tide, atmospheric pressure, sea surface height and tilting of the sensors during data collection were accounted for when converting the pressures into depths of a series of seafloor monuments. The depths were compared from year to year using two different methods to calculate the vertical deformation on the seafloor. Results revealed a pattern of significant uplift of up to 9.0 +/- 2.4 cm/year on the midslope bench region of the Hilina slump and no significant vertical deformation seaward on the outer bench.; Extensive modeling of the data yielded a series of best-fit models. These models were compared with previous models to either affirm or refute them. Previous models that required the offshore portion of the decollement to be locked have been refuted and a shallow fault source has been rejected as the main source generating the observed vertical deformation signal. Models requiring significant seaward slip on a deep decollement fault plane due to volcanic spreading have been affirmed. Our model requires a locked outer bench and significant seaward slip of 25.0 to 28.1 +/- 7.3 cm/year on the offshore portion of the decollement fault plane that continues between 24.8 and 27.0 +/- 0.5 km from the rift zone.