About 30-40 vents have been identified. Most cinder cones on Oahu are quite large, over high and up to wide. Some of the lava flows filled deep valleys cut into the older Koʻolau volcano and displaced streams that previously ran through these valleys; for example, water passing over a lava flow in Kamanaiki Valley forms a waterfall. Together with sediments coming down from the mountains and coral reef growth, the deposits of the Honolulu Volcanics have formed the coastal plain on which the city of Honolulu and military installations are built.