Kauai (kou´wī´), circular island (1990 pop. 51,177), 549 sq mi (1,422 sq km), 32 mi (52 km) in diameter, N Hawaii, separated from Oahu island to the southeast by Kauai Channel. Lihue (1990 pop. 5,536) is the largest town and Nawiliwili Harbor the chief port; most of the island's people live along the coast. Geologically, Kauai is the oldest of the Hawaiian Islands. It was formed by now extinct volcanoes; Kawaikini (5,170 ft/1,576 m high) and Waialeale (5,080 ft/1,548 m high) are the tallest peaks. High annual rainfall has eroded deep valleys in Kauai's central mountain mass. Waimea Canyon (2,000–3,000 ft/610–915 m deep; c.10 mi/16 km long) resembles a miniature Grand Canyon. The northeastern slopes of Waialeale, one of the wettest spots on earth, receive an annual average rainfall of 450 in. (1,143 cm). Tourism is the main industry.
An independent Polynesian kingdom when visited by English Capt. James Cook in 1778, Kauai became part of the Kingdom of Hawaii in 1810. The first major attempt at agricultural development in Hawaii occurred there with the establishment of a sugar plantation in 1835; sugar production ceased in 2009. In Sept., 1992, Hurricane Iniki, the strongest hurricane to hit the Hawaiian islands in the century, devastated the island.