Why is Yap Island geologically different from most other islands in the Federated States of Micronesia?

Yap Island is geologically distinct from most other islands in the Federated States of Micronesia because it is continental in its geologic composition, having been formed by folds in the Earth’s crust.1

While many other islands in the region are volcanic or low-lying coral atolls, Yap's structure is fundamentally different. It is situated west of the Andesite Line, a significant geological boundary in the Pacific that separates continental-type islands—which are rich in andesite and often feature sedimentary rocks—from the oceanic islands to the east, which are primarily composed of basalt.2