Tupua'i is located just north of the
Tropic of Capricorn. The island is at the centre of the Austral Islands, located 195 km from
Ra'ivāvae, 210 km from
Rurutu, 700 km from
Rapa Iti and 640 km south of Tahiti. It consists of two former sets of volcanic peaks on Mount Taita'a (), which are separated by the collar of Huahine (). Its area is , surrounded by a large lagoon, the largest of the Austral Islands. The coral reef that surrounds it in effect creates a lagoon of , an area almost double that of the island. It sometimes reaches wide. Its depth is low, resulting in a characteristic turquoise or jade color. For a large part, its depth is around . However, it can reach up to in some parts of the Southeast. The waters are constantly replenished by a strong, fairly constant ocean current, which helps preserve the lagoon habitat and the health of the coral reef. The generally cooler waters and, until recently, very low pollution have also helped sustain this environment. Many small streams run through the island, though they often empty into swamps rather than the sea. These swamps represent a fairly large portion of the island. Only the river Vaiohuru has any real flow. Eight offshore
motu surround the main island (with an additional 0.4 km2; 100 acres): • Motu One (also known as
îlot de sable (Sandly Islet) in the North) • Motu Rautaro • Motu Toena • Motu Roa (also called Motu Tāpapatava'e) • Motu Mitihā (originally Motiha'a) • Motu 'Ōfa'i (also called
îlot caillou (Rock Island)) • 'Iri'iriroa • Îlot plat (Flat Island) The islets above are listed clockwise from the north of the island. The last two islands are often submerged and hence not visible. The motu 'Ōfa'i is itself the only island that has not formed through coral because it is composed of
basalt, hence its name. It is also the only volcanic outcrop on the island, aside from the main island. ==Climate==