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Surtsey, Iceland Location: 63.4N, 20.3W Elevation: 174 m Last Updated: 16 April 2001 The Island of Surtsey. Photo by B. Edwards. Location of Surtsey. Map courtesy of U.S. Geological Survey. Location of the vents associated with the eruption of Surtsey. Surtla, Syrtlingur, and Jolnir are satellite vents that were active early in the eruption. Syrtlingur and Jolnir formed islands that were eroded away. Surtla grew close to but never above sea level (Kokelaar and Durant, 1983). From Moore (1985). Surtsey is a volcanic island and part of the Vestmannaeyjar submarine volcanic system. Vestmannaeyjar also produced the famous eruption of Heimaey (Eldfell). Surtsey is about 1.5 km in diameter and has an area of 2.8 square km. Surtsey is 33 km south of the main island of Iceland and 20 km southwest of Heimaey. The island is named for Surtur, a giant of fire in Icelandic mythology. Simplified geologic map of Surtsey. Dashed line shows 1991 shoreline. Simplified from Moore and others (1992). East-west cross-section to the two tuff cones of Surtsey. Simplified from Moore (1985). No vertical exaggeration. Surtsey is a classic example of the growth of a new volcanic island. Episodic eruptions began on November 8, 1963 and ended on June 5, 1967. The volcano grew from the sea floor, at a depth of 130 m, to sea level by November 15. During the first few days, eruptions were not explosive and probably consisted of gentle effusion of pillow lava. As the volcano grew towards sea level the water pressure decreased and activity became explosive. Surtsey's crater. Photo by B. Edwards. The early phases of the eruption were phreatomagmatic, caused by the interaction of magma and water. Explosions were closely spaced or steady jets, producing dark clouds of ash and steam shooting tens or a few hundred meters above the vent. At times, a column of ash and steam was carried 10 km above the growing island. A tuff ring was constructed by glassy tephra that was deposited by base surges and by fallout. This new island was unstable because it was made of unconsolidated tephra. On January 31, 1964, activity shifted 400 m to the northwest and phreatic eruptions continued at a new vent. As the eruption progressed, a new tuff ring developed that protected the vent from sea water. On April 4, 1964, this caused the activity to change from phreatomagmatic explosions to lava fountaining and the gentle effusion of lava flows. Lava flows extended the island to the south and protected the underlying tephra from wave erosion. This phase of the eruption ended on May 17, 1965. Surtsey was quiet for more than a year. On August 19, 1966, activity resumed at new vents at the older tuff ring on the east side of the island. More lava flows moved to the south partially overlapping the older flows. The eruption stopped on June 5, 1967. It had lasted a total of 3.5 years. About 1 cubic km of ash and lava had been produced with only 9% of it above sea level. The average temperature of the lava was 1140 C. Surtsey is made of alkali olivine basalt. Between 1967 and 1991, Surtsey has subsided about 1.1 m (Moore and others, 1992). The subsidence is probably the result of compaction of the volcanic material that makes the volcano, compaction of the sea-floor sediments under the volcano, and possibly downwarping of the lithosphere due to the weight of the volcano.
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