Easter island comprises three major volcanoes, Poike a simple strato-volcano, Rano Kau which is of similar size but with a caldera at its summit, and Terevaka which is the largest and most complex of the three. In addition there are about seventy minor eruptive centres. The lavas constitute an alkali-basalt-trachyte-soda-rhyolite series but the acid members are of very restricted development. There is evidence that the parasitic tuff cone of Rano Raraku has had a more complicated history than previous reports have suggested. Although no volcanic activity has ever been reported, some of the lava flows appear to be of very recent origin.