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.

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.

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.

[citation needed] The Vestmannaeyjar archipelago was settled in about 874 AD, originally by escaped Insular slaves belonging to Norse settlers on the mainland.

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.

[citation needed] 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.

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.

"[4] The high viscosity led to a "massive, blocky ʻaʻā lava flow which moved slowly but relentlessly toward the north, northeast, and east.

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.

[6] 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.

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.

[citation needed] By early February, the heavy tephra fall had abated, but lava flows began to cause serious damage.

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, and lava began to flow towards the harbour, a situation which caused serious concerns - if the harbour was blocked, the island's fishing industry would be devastated.

[citation needed] Efforts to mitigate the hazards presented by the accumulation of poisonous gas included the building of a large tephra wall to divert gases away from the town, and the digging of a trench to channel away the CO2 (carbon dioxide).

Lava flows had been sprayed with water in attempts to slow them in Hawaii and on Mount Etna, but these had been rather small-scale operations with limited success.

[citation needed] The pumping capacity was increased in early March, when a large chunk of the crater wall broke away from the summit of Eldfell and began to be carried along the top of the lava flow towards the harbour.

The chunk, dubbed Flakkarinn (The Wanderer), would have seriously threatened the viability of the harbour if it had reached it, and the dredging boat Sandey was brought in on 1 March to prevent its advance.

Sandey was able to spray up to 400 litres per second (105 US gallons per second) onto the advancing flow, and a network of pipes was laid on top of the lava to distribute the seawater over as wide an area as possible.

[citation needed] The work involved in laying pipes over an active lava flow was highly dangerous, with low visibility due to the extensive emission of steam.

[citation needed] The workers dubbed themselves 'The Suicide Squad', and managed to lay pipes up to 130 metres (430 ft) inward from the flow front, directly over the advance.

[citation needed] Sigurgeirsson called these protective measures "undoubtedly the most extensive that have ever been used in a volcanic eruption" and said that "had it not been for the cooling, the lava tongue [into the harbor] could be expected to…extend further along its direction of movement…for a whole month longer than it actually did.

In Europe, the eruption was one of the biggest news items while it continued, competing for front-page space with breakthroughs then being made in the Vietnam War peace talks in Paris.

[citation needed] Short-lived submarine activity was discovered by a fishing vessel on 26 May, about four kilometres (two nautical miles) northeast of Heimaey and 1 km (1⁄2 nmi) off the coast of the mainland.

[citation needed] In total, the volume of lava and tephra emitted during the five-month eruption was estimated to be about 0.25 km3 (330,000,000 cu yd).

[14] Also counter-intuitive, the forced displacement had a large positive causal effect on both the earnings and education for those who were younger than 25 years old at the time of the eruption.

[14] The insides of lava flows can remain at temperatures of several hundred degrees for many years due to the very low thermal conductivity of rock.

Each plant extracted energy from a square 100 metres (330 ft) on each side, by percolating water down into the hot parts and collecting the resulting steam.

Since then, its height has dropped by 18 to 20 metres (60 to 65 feet), due to slumping and compacting of the unconsolidated gravelly tephra as well as wind erosion.