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English: Eldfell is a composite 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 just outside the town of Heimaey on 23 January 1973. Its name means Mountain of Fire in Icelandic.

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 (35 miles) 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. [2] 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 miles), 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,[2] which reached a maximum length of about 3 kilometres (2 miles) during the first few hours of the eruption, but activity soon became concentrated on one vent, about 0.8 kilometre (0.5 mile) 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. [3] The eruption column that caused the air fall “occasionally rose to 9,000 metres (30,000 ft), or nearly to the tropopause”.[2] 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,[3] where small explosions built up a diminutive island that was soon overtaken by the advancing delta.[2] "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."[3] The high viscosity led to a "massive, blocky ʻaʻā lava flow which moved slowly but relentlessly toward the north, northeast, and east." [4]

more about the volcanic eruption en.wikipedia.org/wiki/Eldfell