GENERAL INFORMATION

The Surtsey Eruption 1963-1967

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.

On August 19, 1966, a lava eruption began anew on Surtsey, this time from new craters in the eastern tephra crater; i.e., in old Surtur. Lava flowed from these craters to the east and southeast until the beginning of June 1967, when the Surtsey eruption ceased. From December 1966 until January 1967 there were also eruptions in five different locations in the eastern tephra crater, but lava flow was limited.

When the eruptions had come to an end in June 1967, they had lasted for over three and a half year. The area of the island was 2.7 km² at this time. A total of 1.1 km³ of volcanic products arose from the Surtsey eruption, of which 60-70% were tephra and 30-40% lava.

In many respects the Surtsey eruption is comparable to eruptions that led to the formation of hyaloclastite (palagonite) mountains in Iceland during the Ice Age. Similarities have been observed between Surtsey and table mountains (tuyas). After witnessing the Surtsey eruption, scientists have argued that the Vestmannaeyjar, with the exception of the northernmost part of Heimaey, were formed in similar submarine eruptions as Surtsey.

The core of Surtsey is variably coarse tephra that was formed in explosive eruptions. Above sea level the tephra formed two crescent-shaped craters in the centre of the island. The base of the lava in Surtsey is, to a large extent, made of breccia, which was formed by rapid cooling and marine erosion as the lava flowed into the sea. The eruptions occurred in a total of eight locations on the island. It then follows that under the surface is a net of dikes by which the lava was brought to the surface.

A small ness was formed on the northernmost part of Surtsey. This is a coastal formation that receives material from the lava fields broken down by the ocean on the southern part of the island. The prevailing wind directions ensure that the eroded material is deposited on the northern leeside of the island.

 

See a slideshow of the Surtsey eruption

(author: Sveinn P. Jakobsson – sjak@ni.is)

- last updated 06-May-2007