Its largest and most populated island, [[Tongatapu]], on which the capital city of Nuku'alofa is located, covers 257 square kilometers (99 sq. mi.). Geologically the Tongan islands are of two types: most have a limestone base formed from uplifted coral formations; others consist of limestone overlaying a volcanic base. | Its largest and most populated island, [[Tongatapu]], on which the capital city of Nuku'alofa is located, covers 257 square kilometers (99 sq. mi.). Geologically the Tongan islands are of two types: most have a limestone base formed from uplifted coral formations; others consist of limestone overlaying a volcanic base. |