Almost-atoll of Aitutaki: reef studies in the Cook Islands, South Pacific
Biodiversity Conservation
Available Online
Gibbs, P.E.
,
Stoddart D.R.
1975
Rarotonga and Aitutaki form the summits of separate volcanic masses rising from depths of 4000 m, at which depth the cones are 45-55 km in diameter (Summerhayes and Kibblewh 1966, 1967).The lower slopes of the cones average 15-25 increasing to 30 in the upper 750 m and becoming very steep the surface reef is approached. The Mauke-Aitutaki line of islands is thought to be of early Tertiary age: the surface volcanics are much eroded, with a subdued topography, or are capped with limestones (Wood, 1967; Wood and Hay, 1970). On Rarotonga, where the relief is much stronger (maximum altitude 640 m), radiometric ages of 2.3-2.8 million years date the 1 as Pliocene (Tarling, 1967). Mangaia, with a cap of Oligoce Miocene limestones, must be much older (Marshall, 1927). Evi dence from the deep-sea drilling programme indicates that th ocean floor in the area of the southern Cooks is Paleogene (22.5-65 million years) in age (Winterer, 1973), thus provid a maximum age for the islands. It is probable that the gross history of the Cooks resembles that of other, better-known reef-capped Pacific volcanic cones known to have been initia in the early Tertiary.
