Geology of National Park of American Samoa
The National Park of American Samoa is largely made up of shield volcanoes which were created on one of the Pacific Plate hot spots, emanating progressively from the west to the east. This means that the islands to the east are the youngest, namely Ofu and Ta’u, and are still “works in process” – they are still being built. The largest and oldest of the islands is Tutulia, which is possibly around 1.4 million years old.
The islands of the National Park of American Samoa aren’t solitary volcanoes, each island is not just one volcano, instead they’re a series of shield volcanoes which overlap and were created from the basalt lava flow. These volcanoes probably first emerged during the Pliocene Epoch and were then heavily eroded so all that’s now left are exposed outcrops and plugs. The youngest of the islands in National Park of American Samoa, Ta’u, is actually what’s left when a shield volcano from the Holocene days collapsed, hence the 3000 feet sea cliffs towards the northern side, examples of some of the highest and steepest escarpments to be found anywhere in the world.
The volcanoes within the National Park of American Samoa haven’t been active lately, although the hot spot which still remains below them does give the odd indication of being active, a submarine eruption was recorded as recently as 1973.