The 8 major and 124 minor islands that make up the State of Hawaii were formed by volcanic eruptions. Mauna Loa, on the island of Hawaii, is the world's largest active volcano, at a height of 13,675 ft (4,168 m). Kilauea, on the eastern slope of Mauna Loa, is the world's largest active volcanic crater: beginning on 24 May 1969, it spewed forth 242 million cu yards (185 million cu m) of lava, spreading over an area of 19.3 sq mi (50 sq km). The longest volcanic eruption in Hawaii lasted 867 days. Further indications of Hawaii's continuing geological activity are the 14 earthquakes, each with a magnitude of 5 or more on the Richter scale, that shook the islands from 1969 to 1979; one quake, at Puna, on Hawaii in 1975, reached a magnitude of 7.2.
Hawaii, Maui, Kauai, and Molokai are the most mountainous islands. The highest peak in the state is Puu Wekiu (13,796 ft/4,208 m), on Hawaii; the largest natural lake, Halulu (182 acres/74 ha), Niihau; the largest artificial lake, Waiia Reservoir (422 acres/171 ha), Kauai; and the longest rivers, Kaukonahua Stream (33 mi/53 km) in the north on Oahu and Wailuku River (32 mi/51 km) on Hawaii. While much of the Pacific Ocean surrounding the state is up to 20,000 ft (6,100 m) deep, Oahu, Molokai, Lanai, and Maui stand on a submarine bank at a depth of less than 2,400 ft (730 m).