fresh lava flows giving it further resistance to erosion. The eruption rate diminished steadily, though, and on 5 June 1967, the eruption ended. The volcano has been dormant ever since. 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 above sea level at that time. Since the end of the eruption, erosion has seen the island diminish in size. A large area on the southeast side has been eroded away completely, while a sand spit called Norðurtangi (north point) has grown on the north side of the island. It is estimated that about of material has been lost due to erosion—this represents about a quarter of the original above-sea-level volume of the island. Its maximum elevation has diminished to . Recent development Following the end of the eruption, scientists established a grid of benchmarks against which they measured the change in the shape of the island. In the 20 years following the end of the eruption, measurements revealed that the island was steadily subsiding and had lost about one metre in height. The rate of subsidence was initially about per year but slowed to a year by the 1990s. It had several causes: settling of the loose tephra forming the bulk of the volcano, compaction of sea floor sediments underlying the island, and downward warping of the lithosphere due to the weight of the volcano. Volcanoes in the Vestmannaeyjar archipelago are typically monogenetic, and so the island is unlikely to be enlarged in the future by further eruptions. The heavy seas around the island have been eroding it ever since the island appeared, and since the end of the eruption almost half of its original area has been lost. The island currently loses about of its surface area each year. Future As a suspected part of the Iceland plume, this island is unlikely to disappear entirely in the near future. The eroded area consisted mostly of loose tephra, easily washed away. Most of the remaining area is capped by hard lava flows, which are much more resistant to erosion. 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. On Surtsey, this process has happened quite rapidly, due to high temperatures not far below the surface. Estimates of how long