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