The Surtsey eruption is among the longest eruptions to have occurred in Iceland in historical times. The first sign of an eruption came early in the morning of November 14, 1963, at a site approximately 18 km southwest of Heimaey, the largest of the Vestmannaeyjar (Westman Islands). The eruption is believed to have commenced a few days earlier on the sea floor, at a depth of 130 m. 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 eruption activity moved to the northwest on February 1, 1964, where tephra erupted from young Surtur (Surtungur) until the beginning of April. From December 28, 1963, to January 6, 1964, a submarine eruption was evident in a location approximately 2.5 km east-northeast of Surtsey. A ridge some 100 m high formed on the sea floor. It was given the name Surtla but never grew to become an island, as did Surtsey.
On April 4, 1964, a lava eruption commenced in the western crater on Surtsey. The lava flowed mainly to the south and east and formed a broad lava shield that was, in the end, 100 m thick at the crater. On May 17, 1964, the lava eruption from this crater ceased. By that time Surtsey had grown in area to 2.4 km². 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. Syrtlingur reached a maximum area of 0.15 km², but it did not remain in existence for long. The tiny island was quickly broken down by the ocean and had disappeared completely by October 24, 1965.
Another small island, Jólnir, was formed during Christmas 1965, in an eruption on the sea floor 0.9 km to the southwest of Surtsey. This island was in many respects very similar to Syrtlingur. It was about 70 m high and reached an area of approximately 0.3 km². Jólnir was seen to erupt for the last time on August 10, 1966, and it had disappeared into the depths of the sea by the end of October that same year.