The mostly submarine Vestmannaeyjar volcanic system is the southernmost and youngest volcanic center of the Eastern Volcanic Zone that cuts across E-central Iceland. It consists of a roughly 30 x 40 km group of basaltic islands and submarine cones occupying a shallow shelf off the S coast of Iceland, and was the site of two of Iceland's most noted 20th-century eruptions. The island of Surtsey grew from the ocean floor during 1963-67. The island of Heimaey, 20 km to the NE, was the site of eruptions in 1973, during which lava flows partially overran the town of Vestmannaeyjar and threatened its harbor. Twenty-two postglacial eruption sites are known, and all ten subaerial vents on Heimaey are of Holocene age.