REVIEW AND ANALYSIS OF LATE HOLOCENE COASTAL DYNAMICS AT UPOLU, SAMOA

Sāmoa is believed to have been colonized by small and isolated groups (Burley and Addison 2015; Cochrane et al. 2013) due to the lack of suitable coastal plains (Rieth et al. 2008). Here we argue that late Holocene coastal dynamics were a dominating factor in the limited accommodation space for permanent settlement along Sāmoan coasts. Reconstruction of the late Holocene sea-level history for ʻUpolu Island, Sāmoa is further complicated due to local morphological factors such as differential subsidence rates with distance from volcanic load at the neighboring Savaʻi Island, and the influence of tsunami and storm surge in both building and eroding the sedimentary architecture of the coastal plain (Dickenson 1998; Richmond et al. 2011). A series of auger cores taken along the coastal plain of Satitoa, eastern ʻUpolu reveals a subsurface carbonate sand envelope that extends as far as ~200 m inland from the modern coastline. Dated coral clasts allow us to infer that the carbonate package may have formed as early as 1899-2103 yr BP and prograded seaward as sea-level retreated. A high resolution digital elevation model was used to reconstruct subsurface coastal stratigraphy relative to mean sea-level. Cored carbonate sands were analyzed for grain size and composition was compared to modern beach and lagoon sand to determine the origin of sediment. As sea-level continues to rise into the future, narrow, high island coastal areas may once again be threatened by limited suitable environments.