Kiritimati
- ISS004-E-6253
- 16 January 2002
- 20:58 UTC
Kiritimati (formerly known as Christmas Island) is the largest member of the Line Islands. The island is located within the intertropical convergence zone, just north of the equator, lying around 3,300 km east from Tarawa in the Gilbert Islands and 2,500 km south from Honolulu. Its nearest neighbour in the Line chain is the atoll of Tabuaeran, 285 km to the northwest. Kiritimati is by far the largest of the Line Islands and also has the largest land area (321 km²) of any atoll in the world. It measures approximately 70 km in length with a maximum width of 36 km.
This ancient atoll has lost most of the classical atoll features and today consists of a large, flat, island with a shallow tidal lagoon opening on the northwestern side. A narrow reef platform extends up to 120 m from the shoreline around the entire island.
From Vaskess Bay (at lower left in the above image), the coast of Kiritimati sweeps around the lagoon and past South West Point in a narrow finger of land towards the lagoon entrance at Benson Point. Across the Cook Island and South passages is Bridges Point and the settlement of London. Between Benson Point and Bridges Point sits the the 3.5 ha island of Motu Tabu — an important area for breeding seabirds, as well as being home to one of the islands' few remaining stands of Pisonia grandis. The northern side of the lagoon heads in a northwesterly direction towards North West Point before turning eastwards to Manning Point and onto North East Point. From North East Point the coast turns abruptly southwards, forming the Bay of Wrecks, ultimately connecting to the Southeast Peninsula.
The Southeast Peninsula is an approximately 35 km long 'panhandle' structure, which like the rest of the island, has many land-locked lagoons. In this image they are largely rust-coloured and run along the centre of the peninsula. The north coast (top) of the peninsula has Kiritimati's highest point above sea level — where the coastal dunes reach a height of 13 m. The peninsula averages about 10 km across.
The lagoon of Kiritimati has a highly complex structure and is generally very shallow with numerous coral patches, banks and sand bars. The more open and deeper waters of the lagoon's western sections are lined by lagoon flats and lagoon dunes, particularly on the northern side (see North West Point image). The lagoon changes in nature as one moves eastwards, becoming a shallow maze of interconnected pools, coralline ridges and islands. This area of interconnecting lakes in the interior is thought to have formed as a reticulate lagoon, with its reefs flourishing between 4,500 and 1,500 years ago, when sea levels were up to 1 m higher than present. In total, the lagoon complex covers 160 km² in area.
The interior of Kiritimati, like its lagoon, is a maze of land and water. Here, there are hundreds of land-locked shallow lagoons (darker bodies of water in the image), that often exhibit reddish, brown and orange colors. These are of varying salinities with many of them being extremely hypersaline.
The shallow ponds of Kiritimati are mainly filled by periodic heavy rainfalls. When the normally dry conditions resume, heavy rates of evaporation lead to the development of hypersaline conditions. Within the ponds deposits of evaporitic minerals (such as carbonates, calcium sulphate and halite) are laid down in thick microbial mats that line the bottoms of the ponds. It is these evaporite deposits and heavy bacterial growth that lend the ponds their broad range of colours.
Kiritimati is an internationally significant habitat for seabirds, with up to 20 species breeding on the island. Although numbers have declined in recent years, the island still has highest species diversity and largest bird population of any oceanic island in the world — up to 6 million birds can be on Kiritimati during the peak of the breeding season — including 3-4 million pairs of Sooty Terns (Sterna fuscata).
Vegetation on the island consists of tall and dwarf scrub, grassland and herb communities, as well as large areas that have been turned over to coconut plantation.
Synonyms: Christmas Island
image: earth sciences and image analysis laboratory, nasa johnson space center
