Heimaey, 22 January 1973

The Vestmann Islands rise above a submerged plinth of erupted materials that stretches southwestwards from the zone of contemporary volcanic activity in Iceland. Heimacy, the largest and oldest, covers only 16km2, and Surtsey, formed between 1963 and 1967, is now the second largest. All except the northern ridge of Heimaey, formed in the last ice age, were built above sea level during the past 10000 years. However, apart from a small submarine eruption in 1896, the archipelago had not recorded volcanic activity since the settlement of Iceland in AD 874 until Surtsey erupted. Heimaey is dominated by the northern ridge which shelters Vestmannaeyjar, the main settlement on the island. The rest of Heimaey forms a low plain rising southwards to two younger cinder cones, Saefell and Helgafell, which erupted just over 5000 years ago.

When Surtsey erupted, the people of Heimaey were worried that volcanic activity would spread along the fissures to their own island. They had to wait just less than a decade. At 01.55 on 23 January 1973, lava-fountains forming a brilliant vermilion curtain burst more than 200m into the air along an 1800m fissure on the eastern slopes of Helgafell. The eruption was preceded by some 30 hours of earth-tremors repeated with increasing intensity and frequency, which gave warning that magma was rising to the surface. On 24 January, the lava-fountains waned and a Strombolian eruption began which expelled ash, lapilli and bombs, while basalts flowed eastwards to form a delta in the sea. Next day, activity had focused on one vent at the northern end of the fissure, where ash and lapilh, ejected every 1-3 seconds, rapidly formed a cinder cone and also showered down on Vestmannaeyjar, whose outskirts were less than 1 km from the new volcano, Eldfell ("fire mountain"). On 26 January the cone was already 1 00m high, and hot ash set fire to some houses and crushed others under its weight in the eastern parts of the town. The fissure also lengthened to 3km with renewed lava-fountaining, 150m high, that enabled lava to flow in a more threatening direction towards the town. At first, both flows and fragments were discharged at high rates and were often accompanied by carbon dioxide. By 30january 1973, the cone already reached 185m, lava-flows had added 1 km2 to the east of the island, and 2 million m3 of ash had fallen on Vestmannaeyjar. On 19 February, the northern sector of the crater wall of Eldfell collapsed and the breach directed yet more lava towards the town. From late February 1973, however, the eruption waned. Initial lava discharge rates of 100m 3per second fell to 10m3 per second in March, and emissions became so feeble by April 1973 that the end of the eruption was hardly noticed. But the lava-flows were still proceeding through the town to the harbour, whose entrance was now only 30m wide. It was only saved by human intervention and the end of the eruption in spring 1973.

In a sense, Heimaey was lucky. If the fissure had opened 1km farther north, for instance, Surtseyan explosions would have occurred in the harbour entrance and probably obliterated the harbour, the fishing fleet, and the town as well. Evacuation would then have been very difficult, and casualties probably inevitable.

The Strombohan eruption that occurred (with a moderate spread of fragments and rather slowly moving lavas) was of the kind where human initiative was likely to be most successful. Nevertheless, the disaster was well handled, because those in charge knew what to do. Organization and forethought left little place for panic. The whole population of 5300 on the island was evacuated to temporary accommodation on the mainland within seven hours, using the 77 fishing boats sheltering in the harbour from a storm that luckily had just ceased. The sick and the old were moved by air. Then the cattle and the cars, US$l million worth of deep-frozen fish stored near the harbour, the money in the bank and municipal documents were transferred mainly to Reykjavik. A seven-person committee was set up to direct operations. The national bank released immediate funds for the evacuees, parliament increased taxes to pay for the expenses of the disaster, the government gave US$2 million, and more funds came in later from foreign governments and charitable institutions. From the onset of the eruption, only police and those with useful technical ability remained on the island, with suitable vehicles and equipment, although others were later allowed to return in organized groups to remove possessions from their threatened houses.

As the eruption developed, the dangers to be combatted were three-fold: poisonous gas, falling fragments, and lava-flows, which eventually assumed the greatest importance. Invisible, lethal, ground-hugging carbon dioxide swirled from the fissure and lurked in the cellars of Vestmannaeyjar for many days, often obliging those combatting the eruption to wear gas masks and avoid low-lying places.

The danger from falling fragments was more apparent in the first weeks of the eruption, when bombs and cinders damaged rooftops and broke windows, and hot ash often set fire to the houses and buried many others. The first palliative action undertaken, boarding up windows with metal sheets and shovelling ash from roof-top, could not keep pace with a prolonged eruption, although volunteers continued their efforts well into March. In the end, ash and lapilli burned and buried over 80 houses - and three-quarters of them were lost in the first week.

The first lavas flowed eastwards into the sea. If they had continued to flow in that direction, they would have created a few problems apart from warming the fish. But when the fissure lengthened on 26 January 1973 and part of the crater wall collapsed on 19 February, the lavas advanced on the eastern part of Vestmannaeyjar, threatening its harbour entrance, as well as the electric cables and the freshwater conduit from the mainland. The threat to the harbour was all the more important because Vestmannaeyjar was one of Iceland's major fishing ports, accounting for over one-eighth of its fish exports. Initial plans to bomb and breach the eastern flank of the crater, however, were abandoned because, if the west flank had also been disturbed, lava would have been directed straight to the town.

Early in February 1973, volunteers decided to pour sea-water onto the flow and consolidate its snout to slow down its advance. When this proved successful, the government sent out a ship in early March, whose pumps could dowse the lavas much more effectively. Powerful water pumps were then also dispatched from the United States and installed on land. Eventually, 20000m3 of lava was being congealed every hour and the flow stopped advancing. At the same time, ash was swept from the streets and compacted into barriers circumscribing the flow so that it could not spread westwards into Vestmannaeyjar. The preventive measures undertaken thus had some success. In fact, the lavas that reached into the harbour entrance and reduced its width to less than 30m now provide better protection for the fleet.

But it is important to put the success into perspective. The methods used would only be successful with a plentiful water supply on gentle slopes threatened by slowly moving lavas, and without danger from violent explosions. The costs of pumping sea-water and building cinder barriers were high, both in ten-ns of finance and human effort. But the people were determined to fight the volcanic onslaught on their lives. Nevertheless, in spite of all this endeavour, the electricity supply cable was cut, three of the five fish factories at the harbour were destroyed and the lava-flow alone claimed over 300 houses. The lava-flow was only halted, too, when the eruption was ending, when the flow had completed most of its advance, and when rates of discharge had already declined. But the lessons learned at Heimaey served as a basis for more difficult battles in the future. The damaged parts of the town have now been rebuilt and the population has almost reached its former total. Seismometers to register any rise of magma have been installed on the mainland and continuously recording tiltmeters have been set up on the island. Regular earthquake activity between Surtsey and Heimaey at a depth of about 20km, however, betrays the presence of magma that threatens more eruptions in the little archipelago.

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