expedition to assess the effects of climate change. In March 2022 a Royal Navy survey by HMS Spey, as part of an effort to update maritime charts regarding British Overseas Territories, found the island to be 1 mile (1.6 kilometres) south of its indicated position. The existing data dates to an aerial survey in 1937, indicating a calculation error when the chart was produced. Natural resources Since the introduction of aluminium-hulled long-boats in the 20th century, Pitcairners have made regular trips to Henderson to harvest the wood of miro and tou trees. Usually, they venture to Henderson once per year, but they may make up to three trips if the weather is favourable. Pitcairners carve the wood into curios for tourists, from which they derive much of their income. Geography Henderson Island is a raised coral atoll that, with Pitcairn, Ducie and Oeno islands, forms the Pitcairn Island Group. The nearest major landmass is the continent of South America, more than away. This coral limestone island sits atop a conical (presumed volcanic) mound, rising from a depth of roughly . Its surface is mostly reef-rubble and dissected limestone – an extremely rugged mixture of steep, jagged pinnacles and shallow sinkholes – and, except for the north end, the island is encircled by steep limestone cliffs up to high. There are three main beaches, on the northwest, north, and northeast shores, and the north and northwest beaches are fringed by reefs. The depression at the island's center is thought to be a raised lagoon. There is only one known potable water source, a brackish spring on the north shore exposed at half tide, rising from a crevice in flat rock, large surfaces of which compose the face of the beach. The surrounding ocean tidal range is about one metre at spring tide. Flora Apart from five species bordering the beaches, including coconut palms, the vegetation is undisturbed. Henderson Island is covered by 5–10 m tall tangled scrub forest, more thinly covered in the central depression. It has 51 native species of flowering plants, ten of which are endemic to the island. Dominant tree species include coconut palms, Pandanus tectorius, Thespesia populnea (miro), Heliotropium foertherianum, Cordia subcordata (tou), Guettarda speciosa, Pisonia grandis, Geniostoma hendersonense, Nesoluma st-johnianum, Hernandia stokesii, Myrsine hosakae, and Celtis sp. Fauna Birds The island is home to four extant endemic land bird species – the Henderson fruit dove, Henderson