Rurutu reconsidered: the development of Makatea topography in the Austral islands

Abstract

The islands of the southern Cook and Austral groups in the South Pacific exhibit astonishing differences in geology and topography, even between closely adjacent islands of similar ages. Some are sea-level atolls, others have low fringes of Pleistocene raised reefs, and others substantial rims of elevated mid-Tertiary limestones, locally known as makatea. On some islands the relief of the makatea is subdued, but on others it is dominated by eroded volcanics, sea-level swamps, and vertical limestone walls. Sixty years ago there was great controversy over whether the makatea of Rurutu represented a reef-growth or an erosional topography. Using insights from Mangaia in the southern Cooks we argue that the makatea relief of Rurutu is of erosional origin, and we identify why the Paparai Valley - seen as a key area in the old arguments, even though none of the protagonists had seen it - holds a key to the great inter-island differ- ences which exist in makatea topography in this part of the Pacific.