Geography of the Marquesas Islands
The Marquesas Islands are the island group farthest from any continent in the world, lying between 400 and 600 miles (600 and 1,000 km) south of the equator and approximately 1,000 miles (1,600 km) northeast of Tahiti. They fall naturally into two geographical divisions: the northern group, consisting of Eïao, Hatutu (Hatutaa), Motu One, and the islands centered on the large island of Nuku Hiva: Motu Iti (Hatu Iti), Ua Pou, Motu Oa and Ua Huka, and the southern group of Fatu Uku, Tahuata, Moho Tani (Motane), Terihi, Fatu Hiva and Motu Nao (Thomasset Rock), clustered around the main island of Hiva `Oa.
With a combined land area of 1,274 km² (492 sq. miles), the Marquesas are among the largest island groups of French Polynesia, Nuku Hiva being the second largest island in the entire territory, after Tahiti. With the exception of Motu One, all the islands of the Marquesas are of volcanic origin.
In contrast to the common perception of lush tropical vegetation that goes culturally hand-in-hand with the appellation "Polynesia", the Marquesas are remarkably dry islands. Although the islands lie within the tropics, they are the first major break in the prevailing easterly winds spawned from the extraordinarily dry (from an atmospheric perspective) Humboldt Current. The annual rainfall is generally around 1,270 millimetres (50 in), but this average is misleading because of very high variability. In La Niña years, rainfall can decline to less than 500 millimetres (20 in), whilst in El Niño years when the ocean warms it can reach 2,800 millimetres (110 in). Unlike the rest of French Polynesia, most rain falls during the cooler months, with May to July usually the wettest and November the driest.
Because of their exceptionally variable climate, the islands are subject to extreme drought and flood conditions. Only those which reach highest into the clouds (generally, above about 2,500 feet above sea level) have reliable precipitation. This has led to historical fluctuations in water supply, which factor has played a crucial rôle in the sustainability of human populations in certain sections of the various islands throughout the archipelago. This is especially evident in the low historical population of Ua Huka (maximum elevation 2,812 ft.) and the intermittent inhabitability of Eiao (maximum elevation 1,890 ft.).