Surtsey

The island of Surtsey in 1999

The future of Surtsey

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 slumping vertically and had lost about a metre in height. The rate of slumping was initially about 20 cm per year but slowed to 1–2 cm 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.[8]

The typical pattern of volcanism in the Vestmannaeyjar archipelago is for each eruption site to see just a single eruption, 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 its original area has been lost. The island currently loses about 10,000 square metres of its surface area each year.[9]

Other islands in the archipelago show the effects of centuries of erosion

However, the island is unlikely to disappear entirely in the near future. The eroded area consisted mostly of loose tephra, easily washed away by wind and waves. 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.[10]

While the island will undoubtedly get smaller yet, it will nonetheless probably persist for many centuries before being eroded away completely. An idea of what it will look like in the future is given by the other small islands in the Vestmannaeyjar archipelago, which formed in the same way as Surtsey several thousand years ago, and have eroded away substantially since they were formed.[9] In 2001, the Icelandic government submitted the island to be listed as a UNESCO World Heritage Site.[11]