Distribution of Drift Pumice as an Indicator for Pollutant Distribution and Sediment Transport in New Caledonia

In 2008 and 2010, felsic drift pumice was collected from a total of 40 beaches around the main island of New Caledonia, Southwest Pacific. This island is enclosed by a barrier reef lagoon whose 2008 designation as a UNESCO World Heritage Site brought attention to the ongoing environmental degradation caused by a century of open cast nickel mining. This type of mining is notorious for producing voluminous fine grained waste sediment that clogs rivers and bays, and may compromise the lush biodiversity of the lagoon. This study examines the use of exotic drift pumice as a visual marker of sediment transport in and around the lagoon. The frequent, voluminous pumice eruptions in the Southwest Pacific provide ample source material that is somewhat durable, highly transportable in water, and easy to collect and analyze. Geochemical and mineralogical analyses were used to identify the source of the pumice in order to map the transport vector across the open ocean and into the lagoon. Pumice characteristics (abundance, angularity, and maximum clast size) were used in conjunction with beach parameters (width, composition, distance from the reef, etc.) to identify at risk coastal areas exhibiting elevated fluvial input in conjunction with reduced marine influence.