Kao is an island and stratovolcano in the Haʻapai island group of Tonga. It lies about 6 km north of Tofua island and reaches 1,030 m above sea level, the highest point in Tonga. The date of its last eruption is unknown. Although Kao does not display fresh-looking lava flows, it is likely very recent in origin due to the absence of deep gullies or high sea cliffs. The slopes of the island rise at angles exceeding 35 degrees to the summit, which has a series of small volcanic craters.