Niuafo'ou is the most northerly island in the kingdom of Tonga.The island is located in the southern Pacific Ocean between Fiji and Samoa, 574 km north of Tongatapu island group and 337 kilometers northwest of Vava'u. It is still an active volcano. The island ring encloses two lakes. The larger, Vai Lahi, is a crater lake 23 metres above sea level, 4 kilometres wide, and 84 metres deep. The lake contains three islands and a submerged island that appears when the water level drops. Vai Lahi is separated from the smaller Vai Si'i by a desolate landscape of sand hills. The island is covered by forest on the inner walls of the crater lake, and on the island's eastern and western slopes.