Z. Geomorph. N.F. Suppl.-Vol. 131 43-57 Berlin. Stuttgart May2003 Interpreting features of carbonate geomorphology on Niue Island, a raised coral atoll P.Terry and P. D. Nunn with 9 figures and 1 table Summary. Remote Niue Island in the south-westPacific is an isolated high carbonate island,formed by the uplift of a coral-capped submarine volcano overthe past 500000years. The distribution of various bedrock lithologies reveals the island's atoll origin, with in situ coral and algal limestones forming a c.70m elevated rim (former atoll reef), enclosing a c.35m central depression underlain by cementedcalcareous and fossiliferous sands (former lagoon floor). Much of the latter was dolomitised by interaction with hypersaline brine as slow emergence cut off the atoll lagoon from the sea.Major featuresof the carbonate geo- morphology are a basin-and-rim structure, steep-walled coastalchasms and well-developed cavesystems with abundant speleothems. This paper examines the origin of these features, highlights problems with their interpretation and proposes some new ideas.Uplift, subma- rine landslides and marine erosion,and the effectsof solution, are superimposed on an atoll terrain controlled by Quaternary emergence and tectonism. Introduction Although there are a large number of both wholly carbonate and makatea-type (composite) carbonate/volcanic islands in the humid tropical South Pacific, there has beenlessattention given to Oceania in the karst literature than elsewhere. The work by aLLIER (1975) on the Trobriand Islands of PapuaNew Guinea, STRECKER et al. (1986) on Santo island in Vanu- atu, and MONTAGGIONI et al. (1985) on Makatea in French Polynesia arenotableexceptions. This is in part a function of the remoteness and difficulty of access for research of most of the small 'outer' islands of the South Pacific. This study describes some featuresof the carbonate geomorphology of Niue Island, an emerged atoll lying 19°5, 169°W in the central SW Pacific (Fig. 1). Niue consists of a Quaternary carbonate cap which grew as an atoll reef on top of a Miocene-age submarine volcano founded in the oceanic crust of the Pacific Plate.This is a useful location to exam- ine featuresof insular limestone geomorphology in the humid tropics for the following rea- sons: (1) Niue is one of the world's largestuplifted coral atolls with a land area of 259 km2, and has a maximum thickness of 68 m of limestone abovesea level and more than 500 m below sea level. The expanseand thickness of porous coralline limestone gives a large 0044-2798/03/0131-0043 $ 3.75 @ 2003 Gebriider Borntraeger, 0-14129 Berlin. 0-70176 Sruttgart