Eldfell is a volcanic cone just over 200 metres (660 ft) high on the Icelandic island of Heimaey. It formed in a volcanic eruption, which began without warning on the eastern side of Heimaey, in the Westman Islands, on 23 January 1973. The name means Hill of Fire in Icelandic.
The eruption caused a major crisis for the island and nearly led to its permanent evacuation. Volcanic ash fell over most of the island, destroying around 400 homes, and a lava flow threatened to close off the harbour, the island's main income source via its fishing fleet. An operation was mounted to cool the advancing lava flow by pumping sea water onto it, which was successful in preventing the loss of the harbour.
After the eruption, the islanders used heat from the cooling lava flows to provide hot water and to generate electricity. They also used some of the extensive tephra, fall-out of airborne volcanic material to extend the runway at the island's small airport and as landfill on which 200 new houses were built.
Iceland is a region of frequent volcanic activity, due to its location astride the Mid-Atlantic Ridge, where the North American and Eurasian Plates are moving apart, and also over the Iceland hotspot, which greatly enhances the volcanic activity. It is estimated that a third of all the basaltic lava erupted in the world in recorded history has been produced by Icelandic eruptions.
The Vestmannaeyjar (Westman Islands) archipelago lies off the south coast of Iceland, and consists of several small islands, all formed by eruptions in the Holocene epoch. Heimaey, the largest island in the group and the only inhabited one, also contains some material from the Pleistocene era. The most prominent feature on Heimaey before 1973 was Helgafell, a 200 meters (650 ft) high volcanic cone formed in an eruption about 5,000 years ago.
The Vestmannaeyjar archipelago was settled in about 874 AD, originally by escaped Irish slaves belonging to Norse settlers on the mainland.These settlers gave the islands their name, Ireland being west of mainland Scandinavia. Although plagued by poor water supplies and piracy during much of its history, Heimaey became the most important center of the Icelandic fishing industry, having one of the few good harbors on the southern side of the country, and being situated in very rich fishing grounds.
The eruption begins
At about 20:00 on 21 January 1973, a series of small tremors began to occur around Heimaey. They were too weak to be felt by the residents of the island, but a seismic station 60 kilometres (37 mi) away, near the mainland, recorded over 100 large tremors between 01:00 and 03:00 on 22 January that appeared to be emanating from south of Heimaey. The tremors continued at a reduced rate until 11:00 that day, after which they stopped until 23:00 that evening. From 23:00 until 01:34 on 23 January, seven tremors were detected that grew shallower and more intense, while the epicenter moved closer to the town of Vestmannaeyjar. The largest tremor measured 2.7 on the Richter scale.
Small tremors are very common at plate boundaries, and nothing here indicated that they heralded a major eruption. The onset of the eruption was therefore almost entirely unexpected. At about 01:55 on 23 January, a fissure opened up on the eastern side of the island, barely a kilometre away from the centre of the town of Heimaey, approximately 200 metres (650 ft) east of Kirkjubær (Church farm), where the island's church had once been located.
The fissure rapidly extended from 300 metres to a length of 2 kilometres (1.2 mi), crossing the island from one shore to the other. Submarine activity also occurred just offshore at the northern and southern ends of the fissure. Spectacular lava fountaining 50 to 150 metres high occurred along the whole fissure, which reached a maximum length of about 3 kilometres (1.9 mi) during the first few hours of the eruption, but activity soon became concentrated on one vent, about 0.8-kilometre (0.50 mi) north of the old volcanic cone of Helgafell and just outside the eastern edge of the town.
During the early days of the eruption, the rate of lava and tephra emission from the fissure was estimated to be 100 cubic metres per second (3,500 cubic feet per second), and within two days, the lava fountains had built a cinder cone over 100 metres (330 ft) high. The name initially given to the new volcano was Kirkjufell (Church Mountain), owing to its proximity to Kirkjubær. This name was not adopted by the official Icelandic place-naming committee, who chose Eldfell (Fire Mountain) instead, despite local opposition. The fountains’ Strombolian eruptions continued until 19 February, depositing thick tephra over the northern half of the island and adding to the cone until it was 200 metres (660 ft) high. The eruption column that caused the air fall “occasionally rose to 9,000 metres (30,000 ft), or nearly to the tropopause”. Lava flows from the cone traveled north and east to produce a “continuously expanding lava delta” along the east coast of the island and into the harbor, where small explosions built up a diminutive island that was soon overtaken by the advancing delta.
The first lavas erupted by Eldfell had a mugearitic chemical composition but within a few weeks the volcano was erupting less fractionated lavas which had a hawaiitic composition.
By early May, the lava flow was between 10 yards (9.1 m) and 23 yards (21 m) in height. It averaged more than 40 yards (37 m) and in some places was as much as 110 yards (100 m) thick. The flow carried off large blocks from the main cone that had broken off, as well as volcanic bombs. "The viscosity of the lava fragments ejected by the blasts was, for basalt, relatively high. Very little spatter was produced and scoria bombs sometimes broke up explosively in flight (presumably due to rapid vesiculation), and by rapid impact on landing." The high viscosity led to a "massive, blocky ʻaʻā lava flow which moved slowly but relentlessly toward the north, northeast, and east."
Volcanic gases were collected from several locations. Gases collected at sea along the submerged part of active eruptive fissure were dominantly carbon dioxide and gases from cooling submerged lava flows were about 70 percent hydrogen. (Richard & James, 1983) Poisonous gas was found at low areas on the eastern part of Vestmannaeyjar. A wall was constructed between the vent and town to divert the gas, and a long trench was excavated for the steam to escape. However, none of these measures were completely effective. (Richard & James, 1983).
In the early hours of the eruption, the Icelandic State Civil Defence Organisation evacuated the entire population of Heimaey, having previously developed evacuation plans for an emergency such as this. The evacuation was necessary because lava flows were already moving slowly into the eastern side of town, and the whole of the small island was threatened by the likelihood of heavy ash fall.
Because of severe storms in the days before the eruption, almost the entire fishing fleet was in the harbour, a stroke of luck which greatly assisted the organisation of the rapid evacuation. The population was alerted to the situation by fire engines sounding their sirens, and gathered by the harbour with just the small amount of possessions they were able to carry. The first boats left for Þorlákshöfn at about 02:30, just half an hour after the start of the eruption.
Most of the population left the island by boat. Fortunately, the lava flows and tephra fall did not at first affect the island's airstrip (Vestmannaeyjar Airport), and a few people who were unable to travel by boat were evacuated by air—primarily the elderly and patients from the hospital. Planes were sent from Reykjavík and Keflavik to help speed the process. Within six hours of the onset of the eruption, almost all of the 5,300 people of the island were safely on the mainland. A few people remained to carry out essential functions and to salvage belongings from threatened houses. Cattle, horses and sheep on the island were slaughtered. On the mainland, friends, relatives and strangers offered shelter and housing. By the end of the day, all 5,300 people were spread around cities and towns on the mainland.