New Geochemical Diagnostic Methods Point to Pumice Rafts as the Most Likely Source for Niue Soils1

The origin of soils on Niue Island, an uplifted South Pacific former atoll, has long been a subject of debate because the soils are highly radioactive. A new assessment of proposed sources shows that content in the soils of major elements such as Fe and Al rules out erosion of the carbonate buildup or pristine aragonite coral. Subaerial volcanic ash has been previously argued to be a major source and according to a newly employed diagnostic ratio of Fe2O3/Al2O3 it is confirmed as a definite minor contributor. Fe2O3/Al2O3 ratios offer evidence that the most likely major soil precursor is pumice rafted periodically from neighboring seamounts or from the volcanically active Tongan Trench. Pumice raftings likely contributed to the soil formation of other uplifted atolls having configurations similar to Niue Island.