A Century of Change in Mid-Ocean Atoll Islands: Funafuti Atoll, Tuvalu

Abstract

The low lying nature of reef islands and small net area has caused concern for reef islands due to the threats of rising sea level from sea level rise. The main purpose of this research was to analyse the morphological change of reef islands over a period of increasing sea levels from 1896 to 2011 (115 years) in Funafuti Atoll, Tuvalu. The analysis was conducted using a range of geospatial data including 1896 Geologic Surveys, aerial photographs collected between 1943 and 2005 and GPS collected during a site visit in February 2011. To analyse changes, the datasets were imported into a Geographic Information System (GIS) and overlaid to calculate a change. The types of island changes analysed were: the change in net island area, positional change in island centroids on the atoll rim, characteristic planform adjustments and the spatial differences in change within the atoll. Results from the analysis of the 28 uninhabited reef islands in Funafuti Atoll show that over the 115 year timeframe, 72% of islands recorded an increase in area, 4% recorded little to no change and 28% decreased in area. The islands which increased in area were predominantly Type I islands located on the eastern (high energy)atoll rim, while the islands which decreased in area were primarily Type III, located on the western (low energy) atoll rim. In total, 11 characteristic planform adjustments were observed within Funafuti Atoll with some of these adjustments far more substantial than the net area change seen. At long timescales (115 years), islands appear to be relatively stable, with a trend of increasing area. However, analysis over the shorter time periods (e.g. 1971 – 1984) has shown that these islands are highly variable over shorter timescales. High energy events, such as Hurricane Bebe, have shown to be important drivers of change; while the anticipated decline in island area due to sea level rise has not been apparent over the 115 year timeframe.