Tawi-Tawi Island in the context of "Sulu archipelago"

The Sulu Archipelago (Tausug: Kapū'-pūan sin Sūg; Sulat Sūg: كَفُوْءْفُوْأَنْ سِنْ سُوْݢْ‎; Filipino: Kapuluan ng Sulu) is a chain of islands in the Pacific Ocean, in the southwestern Philippines. The archipelago forms the northern limit of the Celebes Sea and southern limit of the Sulu Sea. The Sulu Archipelago islands are within the Mindanao island group, consisting of the Philippines provinces of Basilan, Sulu, and Tawi-Tawi; hence the archipelago is sometimes referred to as Basulta, derived from the first syllables of the three provinces.

The archipelago is not, as is often supposed, the remains of a land bridge between Borneo and the Philippines. Rather, it is the exposed edge of small submarine ridges produced by tectonic tilting of the sea bottom. Basilan, Jolo, Tawi-Tawi and other islands in the group are extinct volcanic cones rising from the southernmost ridge. Tawi-Tawi, the southernmost island of the group, has a serpentine basement-complex core with a limestone covering. This island chain is an important migration route for birds.