Geography of El Hierro

El Hierro is the youngest and westernmost island of the Canary archipelago. It emerged from the ocean roughly 1.2 million years ago, when the other islands had long been built, and that geological youth can be seen across its landscape: steep slopes, lava fields barely touched by erosion, and a coastline dominated by cliffs and small coves. With an area of about 269 square kilometres it is the smallest of the seven main islands, reaching 1,501 metres at Pico de Malpaso. Its volcanic density is extraordinary: some 200 well-preserved cones have been counted, almost one per square kilometre, although only one historical volcano is recognised on land, Lomo Negro, at the western tip.

Geological studies of the western Canaries, such as those by Juan Carlos Carracedo and his collaborators on La Palma and El Hierro, describe the island as a textbook example of growth through volcanic rifts or ridges. El Hierro works in its entirety as an elongated ridge shaped "like a gabled roof", with three structural axes that give it its unmistakable three-pointed star silhouette, a singular case among the volcanic edifices and morphologies of the Canaries. The island edifice grew very rapidly, soon rising to some 2,000 metres in height, but its structure, built of thin lava flows and pyroclasts, proved weak: the relief became unstable and suffered three great gravitational landslides, one on each flank.

The most recent and spectacular of those collapses is the one that created El Golfo, between 20,000 and 15,000 years ago. That gigantic mass landslide decapitated the summit region and produced a bay surrounded by a steep amphitheatre 25 kilometres in perimeter and 5 kilometres wide; beneath the sea it left, like a claw mark, a valley 16 kilometres long descending to a depth of -2,000 metres, with the slipped material banked against the submarine slope. The sea pushed inland as far as the present villages of Tigaday and Los Llanillos, where some wells reveal ancient beaches fossilised by later eruptions. Lava flows subsequently refilled part of the depression, creating the fertile plain that today stretches at the foot of the great cliffs of the Golfo arc.

The volcanic vocation remains alive. In 2011 an intense seismic swarm alerted the population and the authorities, and in October of that year a submarine eruption began off La Restinga, in the Sea of Las Calmas, lasting into 2012. Because it occurred underwater, close to the southern coast, damage to infrastructure was minimal, although the episode significantly affected local fishing and tourism. The submarine volcanic edifice formed in that eruption is named Tagoro, and its seabed has become an international reference destination for scientific diving. The episode, studied by Carracedo and other researchers, provided new lessons on the growth of oceanic islands and on the management of volcanic crises.

Water and vegetation draw the other face of El Hierro's geography. The summits, well above the 900 metres needed to intercept the trade winds, capture moisture from the sea of clouds; yet the island is cut by numerous fractures and faults through which rainwater filters down to sea level, so that no significant aquifers exist at high elevations and water galleries must be dug near the coast. In that context the Garoé or Holy Tree of San Andrés gained universal fame: its leaves condensed the fog —the so-called horizontal rain— and supplied water to the ancient inhabitants; today an interpretation centre explains the phenomenon. The island's volcanic youth also accounts for the abundance of its pine forests.

The vegetation is completed by two emblematic landscapes: El Sabinar in La Dehesa, a wood of centuries-old junipers twisted by the force of the wind, and the humid laurel and evergreen forests of La Llanía, the Frontera rural park and the Mencáfete reserve, together with the Tibataje cliff, refuge of the endangered El Hierro giant lizard. At the southwestern tip, Punta de Orchilla —already shown on maps of Greek tradition and used as a reference by French navigation— was for centuries considered the prime meridian, the western limit of the known world; its lighthouse preserves that memory and gives El Hierro the nickname of Meridian Island.

Human geography is organised into three municipalities. Valverde, the capital, sits in the northern midlands, away from the coast, although its territory includes Puerto de La Estaca, which connects the island with Tenerife. Frontera covers the Golfo arc, with vineyards planted on volcanic sand in La Dehesa and the sanctuary of the Virgen de los Reyes. El Pinar de El Hierro combines the pine forests of the midlands with the volcanic southern shore, where La Restinga, the southernmost village, concentrates the diving centres. Natural pools such as Charco Azul or La Maceta punctuate the coast, and from the La Peña viewpoint, designed by César Manrique, the El Golfo valley unfolds below. UNESCO declared the island a Biosphere Reserve in 2000 and a Geopark in 2014.