Nature and geology of Porto Santo

The highest of the six islets (179 m), off Ponta da Calheta and some 500 m from the shore. Its name comes from lime: its reef limestones — fossil corals 15.2 million years old, carbonate deposits and undersea volcanic rocks 12 to 16 million years old, capped by dune sandstones — were tunnelled with galleries to make lime, an industry that employed a good part of the population in the 19th century; the galleries can be seen from Calheta beach. Geosite, Natura 2000 site PTPOR0001, marine core of the Biosphere Reserve and of the Marine Protected Areas Network: Cory's shearwaters, Bulwer's petrels and storm petrels nest here, and the LIFE project (2010–2015) eradicated its mice. A no-entry zone: landing requires IFCN authorisation; admire it from the sea, by kayak or boat from Ponta da Calheta, where a large cave opens in its flanks.

The nearest of the islets, 380 m off the south-eastern tip; also called Ilhéu do Farol or dos Dragoeiros. A 32 ha rock rising to 111 m, it carries the lighthouse lit in May 1901, the first seen by ships arriving from Europe. Two geosites: Pedra do Sol, a mega pillow lava with radial jointing among submarine flows, 12-to-16-million-year-old fossil limestones and coral reefs; and Cabeço das Laranjas, a heap of fossil calcareous algae — calcareous red algae 15 to 14 million years old — that look like oranges. Colonies of Cory's shearwaters and Bulwer's petrels, exclusive snails Hystricella turricula and Idiomela subplicata; its rabbits were eradicated by the LIFE project. Natura 2000 PTPOR0001, a no-entry zone: visits only with IFCN authorisation — admire it from Portela or by boat.

Facing Ponta da Canavieira at the western tip, a rocky triangle with high cliffs and a flat top (115 m). On its eastern side, Ponta da Chaminé hides a blowhole cave that sprays seawater in heavy swell; to the north, the Furna que Berra "roars" beneath the waves. Remarkable endemic fauna: the tarantulas Hogna biscoitoi and Hogna schmitzi, the snail Leptaxis nivosa, and nesting seabirds. A former lighthouse, now out of use, crowns the islet. Natura 2000 PTPOR0001 and Marine Protected Areas Network: access only with IFCN authorisation.

Since 2020 Porto Santo, its six islets and the island shelf down to 100 m depth have formed a UNESCO Biosphere Reserve: 27,310 hectares, 5,060 on land and 22,251 at sea. The terrestrial core zones are the Natura 2000 sites of Pico Branco (133 ha) and the islets, with the Terra Chã forest core; the marine core surrounds Ilhéu da Cal and Ilhéu de Cima. The reserve holds more than 1,600 terrestrial taxa, including some fifteen plants found only on the island, one of the richest land-snail faunas of any oceanic island (about 82 % endemic), seabird colonies, the monk seal and the loggerhead turtle. Tourism is the leading economic sector: the reserve bets on development compatible with conservation.

The highest point on the western side of the island (283 m), famous for its "piano": a set of almost perfect light-grey prismatic columns that in fact look more like organ pipes. They are lava, a volcanic rock split into prisms by the contraction stresses of magma cooling slowly inside a volcanic conduit; the former quarry that exposed them is geosite, listed as a property of regional value and geological heritage in the municipal master plan. The best vantage point is the Miradouro da Pedreira, close to the golf course and 144 m from the paved road; a footpath starts from the slopes where the São Pedro chapel stands, a 17th-century building altered in the 18th century whose pebble-paved churchyard depicts a caravel. Legend has it that the Ana Ferreira cave sheltered an illegitimate daughter of King João II.

On the north coast, Porto Santo's historic spring: its water, once held sacred, was said to be the purest on the island, and an 18th-century fountain still stands nearby. In the 19th century, together with Tanque and Fontinha, it was one of the island's only three springs. All around, pale sandstone cliffs carved by the wind: dune sandstones, biogenic carbonate sandstones piled up over the last two million years, the oldest about 31,000 years old. Four units separated by palaeosols, calcareous crusts ("laginhas de cal"), root casts and fossil land snails tell of former vegetated landscapes under prevailing northerly winds. Geosite, scientific heritage and a natural area of strongly restricted use, 25 m from the road with easy access. From the viewpoint: Ilhéu da Fonte da Areia and the north coast; this is also where the walk down to the Porto das Salemas pools begins.