SUBMARINE DISCHARGE AND THE ANCIENT INHABITANTS OF EASTER ISLAND

Hydrogeologically, Rapa Nui (Easter Island, Chile) is one of the least understood islands in Polysnesia. There are no surface streams, the soils are highly permeable, and the water table sits far below the surface of the island. One of the many mysteries of Rapa Nui is how the ancient inhabitants survived with so few sources of freshwater. Although impossible, some historic European accounts report the natives actually drank seawater.

The scarcity of freshwater suggests that water resources may have been a constraining factor in settlement growth, patterning, and distribution. Fieldwork was conducted to identify terrestrial sources of freshwater and compare them to early settlement distribution. These data consist of images and GPS locations for observable surface water features located in the interior of the island and field measurements of GPS locations, temperature, and salinity to identify areas of submarine groundwater discharge (SGD) along the coast. Often co-located with areas identified as having SGD are prehistoric catch basins (puna) and historic makeshift pump wells, although there exists many more coastal seeps than there are puna or wells. The limited number of interior surface water features, periods of drought, the permeable aquifer, and the existence of puna along the coast of Rapa Nui lead us to conclude that coastal seeps are an important source of freshwater that would have been available to prehistoric inhabitants of Rapa Nui.