The largest, Vai Lahi, is 23m above sea level, 4km wide, and 84m deep. It has three islands plus a low one which appears when the water level drops. Vai Lahi is separated from the smaller Vai Mata aho by a wasteland of sand hills and opines. The inner walls of the main Crater Lake and the eastern slopes north of Tongamama o have dense forest. Forest is also growing slowly over the lava-covered western slopes.
Coastal vegetation is found on the entire southern coast.
All the rest of the island has coconut palms, trees and mixed agriculture. Niuafo ou has been an active volcano for thousands of years. It is a most unusual volcano because there have been two types of eruptions. Explosions from the craters in the Caldera produce magma. This is surface material carried down by subduction and remelted.