Surtsey Island was formed in an eruption below sea-level. On November 14 1963 the eruption had reached the surface of the Atlantic Ocean, south of the Westmann Islands, of which Surtsey is now the southernmost island. The eruption started about 130 meters (430 feet) below sea level. The eruption lasted until 5 June 1967, when the island reached its maximum size of 2.7 km2 (1.0 sq mi). Since then, wind and wave erosion have caused the island to steadily diminish in size. The most recent survey (2007) shows the island's maximum elevation at 155 m (509 ft) above sea level.
The beginning. Photo: Þorleifur Einarsson.
The Surtsey eruption is among the longest eruptions to have occurred in Iceland in historical times. Explosive phases characterized the Surtsey eruption in the beginning, and due to the rapid cooling effects of the sea, the hot magma transformed into tephra (volcanic ash). The tephra production was tremendous, and an island had already been formed the day after – on November 15. By the end of January 1964, the new island’s elevation was 174 m, or over 300 m above the sea floor where it had all begun.
The lava flowing into the ocean. Photo: Sólarfilma.
At the end of May 1965, a new eruption seemed to be taking place at the bottom of the ocean 0.6 km east-northeast of Surtsey, and on May 28 an island could be seen. This island was called Syrtlingur, and explosion eruptions occurred there until the beginning of October 1965. The tiny island was quickly broken down by the ocean and had disappeared completely by October 24, 1965.
One of the very first photos by Hermann Kjartansson.
Another small island, Jólnir, was formed during Christmas 1965, in an eruption on the sea floor 0.9 km to the southwest of Surtsey. Its fate was similar to Syrtlingur. The eruption ended in June 1967. The island is still closed to all but scientist who study how life develops on an uninhibited island.
Páll Stefánsson was allowed to go to Surtsey in 2008.
The undersea vents that produced Surtsey are part of the Vestmannaeyjar submarine volcanic system, part of the Mid-Atlantic Ridge. Vestmannaeyjar also produced the famous eruption of Eldfell on the island of Heimaey in 1973.
A short video in French of the eruptions in Surtsey in 1963 and Heimaey in 1973 can be seen below: