Since then, wave erosion has caused the island to steadily diminish in size: as of 2012[update], its surface area was 1.3 km2 (0.50 sq mi).

[4] It was intensively studied by volcanologists during its eruption, and afterwards by botanists and other biologists as life forms gradually colonised the originally barren island.

Gradually, as repeated flows built up a mound of material that approached sea level, the explosions could no longer be contained, and activity broke the surface.

[5] The first noticeable indications of volcanic activity were recorded at the seismic station in Kirkjubæjarklaustur, Iceland from 6 to 8 November 1963, which detected weak tremors emanating from an epicentre approximately west-south-west at a distance of 140 km (87 mi), the location of Surtsey.

[6] That same day, people in the coastal town of Vík 80 km (50 mi) away noticed a smell of hydrogen sulphide.

[5] On 13 November, a fishing vessel in search of herring, equipped with sensitive thermometers, noted sea temperatures 3.2 km (2.0 mi) SW of the eruption center were 2.4 °C (4.3 °F) higher than surrounding waters.

[7] At 07:15 UTC on 14 November 1963, the cook of Ísleifur II, a trawler sailing these same waters, spotted a rising column of dark smoke southwest of the boat.

The violent explosions caused by the meeting of lava and sea water meant that the island consisted of a loose pile of volcanic rock (scoria), which was eroded rapidly by North Atlantic storms during the winter.

The loose pile of unconsolidated tephra would quickly have been washed away had the supply of fresh magma dwindled, and large clouds of dust were often seen blowing away from the island during this stage of the eruption.

[9] Three French journalists representing the magazine Paris Match notably landed there on 6 December 1963, staying for about 15 minutes before violent explosions encouraged them to leave.

[10] By early 1964, the continuing eruptions had built the island to such a size that sea water could no longer easily reach the vents, and the volcanic activity became much less explosive.

These resulted in a hard cap of extremely erosion-resistant rock being laid down on top of much of the loose volcanic pile, which prevented the island from being washed away rapidly.

[5] On 28 December 1963, submarine activity to the northeast of Surtsey began, causing the formation of a ridge 100 m (330 ft) high on the sea floor.

[11] In 1965, the activity on the main island diminished, but at the end of May that year an eruption began at a vent 0.6 km (0.37 mi) off the northern shore.

It was named Jólnir, and over the following eight months it appeared and disappeared several times, as wave erosion and volcanic activity alternated in dominance.

[13] Effusive eruptions on the main island returned on 19 August 1966, with fresh lava flows giving it further resistance to erosion.

The total volume of lava emitted during the three-and-a-half-year eruption was about one cubic kilometre (0.24 cu mi), and the island's highest point was 174 metres (571 feet) above sea level at that time.

It is estimated that about 0.024 km3 (0.0058 cu mi) of material has been lost due to erosion—this represents about a quarter of the original above-sea-level volume of the island.

In addition, complex chemical reactions within the loose tephra within the island have gradually formed highly erosion-resistant tuff material, in a process known as palagonitization.

[17] A classic site for the study of biocolonisation from founder populations, Surtsey was declared a nature reserve in 1965, while the eruption was still in progress.

[24] Birds first began nesting on Surtsey three years after the eruptions ended, with northern fulmar (Procellaria glacialis) and black guillemot (Cepphus grylle) being the first species to set up home.

An expedition in 2004 found the first evidence of nesting Atlantic puffins (Fratercula arctica),[25] which are abundant in the rest of the archipelago.

Although Surtsey lies to the west of the main migration routes to Iceland, it has become a more common stopping point as its vegetation has improved.

When a large, grass-covered tussock washed ashore in 1974, scientists took half of it for analysis and discovered 663 land invertebrate specimens, mostly mites and springtails, the great majority of which had survived the crossing.

The hut includes a few bunk beds and a solar power source to drive an emergency radio and other key electronics.