1973 Heimaey Eruption, Iceland

The 1973 eruption on Heimaey was also the second major eruption (the other being Surtsey) definitely know to have occurred in Vestmannaeyjar since the settlement of Iceland in the ninth century, although there is evidence of a submarine eruption in the archipelago in September 1896. ...

The 1973 eruption began just before 1 a.m., January 23, on the eastern side of Heimaey, approximately 1,100 yards from the center of town. A north-northeast-trending fissure rapidly opened to a length of about 1.25 miles, traversing the island from one shore to the other. Spectacular continuous lava fountains (curtain of fire) played in the initial phase of the eruption, but the activity soon consolidated to a small area along the fissure about one-half mile northeast of Helgafell. Also during the first 3 days, submarine volcanic activity occurred just offshore at the north and south ends of the fissure vent. Within 2 days a cinder-spatter cone rose more than 110 yards above sea level and was later named Eldfell or "fire mountain" by the official Icelandic place name committee. The output of lava and tephra (a collective term for fragmental volcanic materials initially airborne, such as ash and bombs) was estimated to be about 130 cubic yards per second. Within a few days after the eruption, strong easterly winds resulted in a major fall of tephra on the town of Vestmannaeyjar, completely burying homes close to Eldfell. By early February the tephra fall slackened markedly, but a massive lava flow approached the eastern edge of the town and threated to fill in the harbor of Iceland's most important fishing port. Also in early February submarine activity just north of the fissure severed an electric power cable and a water pipeline which supplied electrical power and water from the Icelandic mainland. ...

By the end of February the cinder-spatter cone was more than 200 yards high. The central crater of Eldfell fed a massive blocky (aa lava) flow which moved slowly but relentlessly toward the north, northeast, and east. By early May this flow as 10 to 23 yards high at its front, averaged more than 40 yards thick, and was as much as 110 yards thick in places. Its upper surface was littered with scoria (cinderlike fragments of dark cellular lava) and volcanic bombs, as well as large blocks from the main cone which broke off and were carried along with the flow. The largest block soon was dubbed "Flakkarinn" (The Wanderer). Some of these blocks of welded scoria were about 200 yards square and stood 20 yards above the general lava surface and were rafted more than 1,000 yards. Measurements made from a series of aerial photographs taken from the end of March to the end of April indicated that the lava was flowing as a unit about 1,000 yards long by 1,000 yards wide with an average speed of 3 to 9 yards per day.

As the flow advanced to the north and east, large blocks slumped from the cone on February 19 and 20 and moved toward the southeastern part of town. Also in late March a second large lava flow moved northwest on the west side of the main flow and covered many houses and the town powerplant.

By February 8, lava ejection dropped from about 130 cubic yards per second to 80 cubic yards per second; and by the middle of April to about 7 cubic yards per second. As noted before, easterly winds blew tephra over the town during the early stages of the eruption. By January 29, the thickness of tephra varied from less than 1 yard in the northwest part of town to more than 5 yards in the southeast part.

The eruption stopped in early July 1973; flowing lava was no longer visible, although hidden subsurface flow may have continued for a while. ... According to preliminary estimates about 300 million cubic yards of tephra were deposited on and adjacent to Heimaey. ...

The prolonged destruction related to the course of the eruption was twofold: the highly visible destruction of homes, public buildings and installations, commercial properties, and partial infilling of the harbor by tephra falls and lava flows; and the economic and social impact on the residents of Vestmannaeyjar, local commerce, and the national and international economy of Iceland.

Within 6 hours after the eruption began, nearly all of Heimaey's 5,300 residents had been evacuated safely to the mainland. This rapid evacuation was accomplished through the foresight of the Icelandic State Civil Defnese Organization, which had a continency evacuation plan ready for just such a disaster. The fishing fleet in port expediated the evacuation.

Homes and farmsteads close to the rift were soon destroyed by tephra burial or fire from lava bombs and flows. The heavy tephra fall caused severe property damage a few days after the onset of the eruption. Numerous homes were completely buried by tephra, set afire by glowing lava bombs, or overridden by the advancing front of lava flows. Although many structures collapsed from the weight of the tephra, dozens were saved by crews of volunteers who cleared the roofs of accumulated tephra and tacked corrugated iron "shutters" over the windows. ... By early May, some 300 buildings had been engulfed by lava flows or gutted by fire, and another 60 to 70 homes had been buried completely by tephra.