illustration of the upper layers of the earth showing subduction zone and narrowing ocean basin
The ocean closes as a continent with thick crust approaches the subduction zone.
Permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this website. Digital assets without any copyright restrictions are public domain.
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.