Tutuila
- ISS004-E-6769
- 22 January 2002
- 20:14 UTC
Tutuila lies near the centre of the Samoan archipelago, situated 70 km southeast from Upolu and 110 km west from the Manu'a Islands group of Ofu-Olosega and Ta'ū. It is the largest of the islands that make up the US unincorporated territory of American Samoa; the smaller units that make up the territory are all located to the north and east: Ofu (95 km east), Olosega (100 km to the east), Ta'ū (110 km to the east east), Rose Atoll (258 km to the southeast) and Swains Island (355 km to the north).
The island has an elongated form, measuring 31 km in length with widths varying from 11 km in the southwest to 2 km in the centre and east, covering an area of 135 km². The interior is heavily eroded with steep slopes, sharp ridges, ravines and valleys, formed from the coalescence of five ancient volcanoes once active along a number of southwest to northeast trending rift zones. Of these now inactive volcanic centres the Pago volcano is the most dramatic: the western side of its 9 km wide collapsed caldera almost bisects the island and forms Pago Pago harbour on the south-central coast of the island — creating one of the largest natural harbours to be found in the South Pacific region. Overlooking the harbour the tall 'Alava ridge marks the northern head wall of the caldera. The tallest peaks of Tutuila form a central spine to the island, rising to a height of 654 m at Matafao Peak (near the centre of the island), 523 m at North Pioa Mountain and 491 m at Mt. 'Alava.
The most extensive area of flat land is the cliff-lined Tafuna Plain of the southwest coast, where the shallow and muddy Pala Lagoon (Nu'uuli Pala) and the island's airport are located (both features are visible on the right side of the above image). The Tafuna Plain is the most recent volcanic feature on the island.
The coastline of Tutuila is generally rugged with steep slopes and low cliffs, headlands and small bays. From the coast an extensive shallow bank extends around the island covering an area of some 300 km² with depths of less than 60 m, before dropping nearly 5,000 m to the ocean floor.
Offshore from Tutuila are a number of smaller islands, islets and rock formations. Of these, the 1.6 km² island of Aunu'u — located 1 km off the southern coast of the eastern end of the island — is the largest (see large size image).
image: earth sciences and image analysis laboratory, nasa johnson space center
