How were most of the islands of American Samoa formed?

With the exception of the coral atolls, the islands of American Samoa were formed by volcanic activity occurring within the past seven million years. These volcanic origins result in interiors that are high and rugged, with the main island of Tutuila rising steeply above deep inlets. While volcanic processes created the majority of the landmasses, coral reefs are common at the extremities of the islands, and the territory also includes coral atolls such as Rose Atoll and Swains Island.12