One of the most iconic works of land art was the giant spiral-shaped jetty realised by Robert Smithson in 1970 on the north shore of the Great Salt Lake, in the desert of the American state of Utah. Some 5,000 tons of black basalt were needed to make this sculpture, which has since been subject to the changes and rigours of nature and the climate. The spiral, which turns anti-clockwise, has at times been submerged under the water and at others completely uncovered. Smithson’s own voice tells the story of the construction work.