Sea-level rise and vertical land motion on the Islands of Oahu and Hawaii, Hawaii

Abstract

Sea-level rise is a highly publicized issue in the Hawaiian Islands because it is one of the main drivers for coastal hazards. In our study, multiple geodetic and in situ datasets are integrated to investigate the sea-level rise and vertical land motion on the islands of Oahu and Hawaii, Hawaii. The rates of relative sea-level changes are derived from the tide-gauge stations in the Hawaiian Islands, however the station located at Kawaihae, Hawaii presents a much higher trend than other stations. Our analysis shows that the questionable trend results from the sudden movement of the equipment on land, which is caused by a pair of earthquakes. After adjustment, we arrive at a revised and more consistent relative sea-level trend at this station. Our study shows that Oahu is vertically ‘stable’ (i.e., near-zero vertical land movement within uncertainties), and the relative sea-level change is dominated by the absolute sea-level change. However, the island of Hawaii was subsiding at −3.3 ± 0.9 mm/year before 1973 and changed to −1.2 ± 0.2 mm/year after 1975, which may relate to seismic activities and where relative sea-level change is attributed to both absolute sea-level change and vertical land motion. The difference in relative sea-level change between the islands of Oahu and Hawaii is due to the difference in vertical land motion rather than steric sea-level change. In addition, the ocean-mass components are the predominant factors that influence the long-term trends of absolute sea level on the islands of Oahu and Hawaii.