Hawaii Island, often called the Big Island, is almost twice as large as the rest of the islands combined. Roughly triangular in shape, it extends 150 km (93 mi) from north to south and 122 km (76 mi) from east to west. The island is a huge mountainous mass dominated by two great volcanic peaks, Mauna Loa and Mauna Kea. In addition to its great bare lava beds and barren ash-covered slopes, which cover much of the island, Hawaii has large areas of tropical rain forests, numerous waterfalls, and great stretches of rolling grasslands.
Hawaii Volcanoes National Park, established in 1916 on southern Hawaii Island, Hawaii, contains two active volcanoes, Mauna Loa and Kilauea. Mauna Loa, the world's largest volcanic mass, towers 4,170 m (13,680 ft) above sea level. Its summit crater, Mokuaweoweo, has walls rising to about 180 m (600 ft); eruptions occur here and from the fissures and newer craters that have formed on the slopes of the mountain. Kilauea projects from the eastern slope of Mauna Loa; it rises 1,247 m (4,090 ft) above sea level. The east rift of Kilauea has been erupting continuously since 1983. Kilauea's crater covers more than 10 sq km (4 sq mi) and is the largest active volcanic crater in the world. Its vast inner pit, Halemaumau, is sometimes called the "House of Everlasting Fire." The park's varied landscape includes the Kau Desert on the arid leeward (eastern) slope of Kilauea and a luxuriant tree fern forest on its moist windward (western) slope. Hawaii Volcano Observatory (established 1911) is on the rim of Kilauea Crater. Until 1961, Hawaii Volcanoes National Park was combined with Haleakala National Park on Maui Island as Hawaii National Park. Area, 84,861 hectares (209,695 acres).