The field appears to consist of some central younger lava flows which are surrounded by older lava flow fields. Based on the thickness of manganese, palagonite and sediment cover on lava flows, it appears that younger flows are 10,000-1,000 years old, while the older flows may be over 10,000-100,000 years old; in general the thickness of manganese crusts is comparable to these found on Mauna Loa, Kilauea and Loihi rocks. Another age range cited in the literature is 14,000-20,000 years ago. It is possible that magma ascended to the surface mainly in areas where the lithosphere has anomalous properties and is more likely to crack rather than to flex; this would explain why the vents of the South Arch volcanic field coincide with Cretaceous seamounts.