contains the Vaipaee valley. The second caldera, included in the eastern half of the first, reaches 857 meters at Mount Hitikau, the highest point on the island. Its diameter is about 5 km and its age is estimated to be between 2.9 and 2.8 million years old. It contains the Hane and Hokatu valleys. The island then underwent another volcanic period in the southwest (Tepeopo scoriaceous volcano and Tahoatikihau Hawaiian volcano) dated around 1.6 - 1.4 Ma. This shows a long geological activity compared to the other islands, at least 1.5 Ma. Tahoatikihau crater contains a fossil lava lake. At the western end of the island there are several sea caves. Flora The vegetation of the plateaus of Ua Huka is poorer than that of the other Marquesan islands. Especially the northwestern part of the island, corresponding to the outer side of the large crater. Unlike the plateaus and hills, the valleys have a much more exuberant vegetation, similar to that of the other islands of the archipelago. This diversity has been enhanced by the creation of the Papuakeikaa arboretum near Vaipaee. This unique achievement in Polynesia brings together more than a thousand species of trees from all over the world, including one of the largest collections of citrus trees in the world (almost three hundred varieties). It is intended to serve as a reserve for the reforestation of the island. The impoverishment of the vegetation is largely due to domestic animals introduced by man, which have then been reintroduced into the wild. Goats, pigs and horses have largely destroyed the vegetation. Ua Huka proudly calls itself the "Island of Horses", but the serious damage they have caused is hidden. In the valleys there are small remnants of the original rainforest, consisting of Hibiscus tiliaceus, Piper latifolium and Metrosideros and Weinmannia. In the humid and shady areas of the narrow gorges grow lush masses of moss and ferns. In the west of the island, the rainforest changes to a drier forest, composed mainly of hibiscus, pandanus, guavas and glochidion. In the lower areas of the large valleys, coconut and breadfruit trees have been planted. There is still a remnant of Pisonia grandis in the lower reaches of Hane Bay. The short valleys of the north coast are almost devoid of vegetation, and the upper parts of the mountains are even arid and desert-like. Fauna Because of the sparse vegetation, there