Northwestern Hawaiian Islands
The Northwestern Hawaiian Islands (sometimes referred to as the Leeward Islands) are the westernmost
islands of the Hawaiian Archipelago. They run in a straight northwesterly line from the main Hawaiian
Islands stretching for around 1,900 km across the North Pacific. They consist of 10 groups of islands,
atolls, shoals and reefs. From east to west they include: Nihoa, Necker Island,
French Frigate Shoals, Gardner Pinnacles,
Maro Reef, Laysan Island,
Lisianski Island, Pearl & Hermes Atoll,
Midway Atoll, and Kure Atoll. In total there are 33 islands
and islets amongst the Northwestern Hawaiian Islands; all are small and have a combined land area of roughly
14 km².
Volcanic in origin, the Northwestern Hawaiian Islands once emerged high above sea level as a chain of shield volcanoes in the same way that the main Hawaiian Islands do today. However, these ancient volcanoes have slowly slipped back into the sea as a result of a sagging of the ocean floor and the ongoing forces of erosion.
The islands are the central grouping of chain of seamounts that form the 6,000 km long Hawaiian-Emperor chain — one of the main ocean floor topographical features of the northern Pacific. The main Hawaiian Islands to the southeast are the youngest members of the chain — some of these are volcanically active and thus still actively growing. The Emperor Seamounts to the northwest are, by contrast, all completely submerged "dead" seamounts. They form the oldest members of the chain, with ages ranging from around 35 to 80 million years. The Northwestern Hawaiian Islands occupy the middle-ground in terms of age and topography, ranging in age from the 7.2 million year old Nihoa at the southeastern end of the chain to Kure Atoll at the northwestern end which is estimated to be around 30 million years old.
The Northwestern Hawaiian Islands are an extremely important group of remote ocean ecosystems that provide habitat for numerous endangered species. More than 14 million Pacific seabirds, including most of the world's Laysan Albatross (Diomedea immutabilis) and Black-footed Albatross (Diomedea nigripes) return to the Northwestern Hawaiian Islands to breed. 17 other species of seabirds also nest in the islands. As well as prolific bird populations these islands are also critical habitats for Green Turtles (Chelonia mydas), Hawksbill Turtles (Eretmochelys imbricata), Leatherback Turtles (Dermochelys coriacea) and the highly endangered Hawaiian Monk Seal (Monachus schauinslandi). Under water too, the islands are extremely important: they are home to around 60-70% of the US's coral reefs, with a total reef habitat cover of around 11,000 km². These reef environments, although not as diverse as other Pacific reefs, contain a high number of endemic species — up to a quarter are thought to be unique to the islands.
Many of these fragile reefs and islands experienced extensive damage in the late 19th and early 20th centuries by the activities of guano mining and hunting, and by the introduction of alien species; many species unique to the islands became extinct or critically endangered. Today, most of the islands are protected as a system of strict wildlife refuges. Recently, the waters and submerged lands of the islands (except Midway, which forms the Midway National Wildlife Refuge) were protected as part of the new Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve — protecting an area in the region of 340,000 km².