Kao is a small volcanic island in the South Pacific and part of the island nation of Tonga. It is located in the eastern Haapai group and 3.4 km northeast of the larger neighboring island Tofua. Kao is about 5 km long, 3 km wide and has an area of 11.6 km ². The island consists of a steeply rising out of the sea and volcanic cone with a height of approximately 1,030 m ( 1,046 m) the highest point in Tonga.
An eruption of the volcano has not been documented. However, since there are no signs of advanced erosion, must the volcano geologically to have been active until recently. The lower slopes are forested Kaos, the upper part against bare.
The only somewhat flatter area of the island in the southwest, there is also the settlement Topuefio. However, there are no permanent residents, according to 2006 census.