Geography of Tenerife

Tenerife, the largest of the Canary Islands, covers some 2,034 km² in a roughly triangular outline: its longest side, about 81 kilometres, faces southeast, and the shortest, about 44, faces west. At its centre rises Mount Teide, which at 3,715 metres is the highest peak in Spain and the great organiser of the island's territory. Few geographies concentrate such a difference in elevation in so little space: barely a few dozen kilometres separate sea level from the high mountain, and that verticality explains almost everything else, from the distribution of rainfall to the location of crops and population.

The island emerged some 7.5 million years ago, and its volcanic activity was concentrated around three structural axes which, starting from the northeastern, northwestern and southern extremes, first formed a small sub-archipelago before converging at the centre. From that initial phase remain the ancient massifs of Anaga, Teno and Adeje, stacks of basaltic lava flows crossed by dense networks of dykes where Tenerife's oldest formations outcrop. Volcanism later shifted to the ridges: the great Pedro Gil ridge, a gable-roof-shaped edifice linking the Vega of La Laguna with the centre of the island, and the northwest ridge or Cumbre de Vilma, the zone of most recent volcanic activity.

At around 2,000 metres of altitude, in the widest part of the island, the Pedro Gil divide gives way to the broad depression of Las Cañadas, the headwall of a colossal landslide that occurred some 180,000 years ago, when a volcanic edifice exceeding 4,000 metres collapsed northwards. The resulting caldera is bounded to the south by an escarpment of about 17 kilometres whose highest point, Guajara, reaches 2,715 metres, the second-highest summit in the archipelago. The spine of the Roques de García separates two enclosures: in the western one extends the Ucanca plain, the largest sedimentary plain in the islands, and along the wall lie the small enclaves known as cañadas, ancient livestock passageways. Over this amphitheatre grew the Teide-Pico Viejo stratovolcano, which closes the depression to the north and makes it the highest and most extensive endorheic basin in Macaronesia.

Volcanism reaches into historical times. Since 1430 six eruptive episodes have been recorded: the Taoro eruption, in the Orotava Valley, preserved by Guanche oral tradition; the one observed in 1492 from Columbus's ships bound for the Indies; the 1704-1705 fissure that opened the volcanoes of Siete Fuentes, Fasnia and Montaña de las Arenas or Güímar; that of 1706, whose lavas destroyed Garachico and the island's only natural harbour; the Narices del Teide of 1798, nine vents opened on the slopes of Chahorra or Pico Viejo and described by Humboldt; and finally Chinyero, in 1909, whose ashes reached Puerto de la Cruz, more than 25 kilometres away.

The climate is the work of the trade winds. These regular northeasterly winds, laden with moisture, strike the northern slopes and form the sea of clouds, which settles roughly between 500 and 1,200 metres and stratifies the mountain into vegetation belts. Along the coastal strip grows the xerophytic zone of cardón and tabaiba scrub; above it, the thermophilous forest and, within the mist belt, the laurel forest and the fayal-brezal heath; above the sea of clouds, where conditions become drier and colder, stretch the pine forests — in Vilaflor pines older than the conquest survive — and on the summit the broom and exclusive species such as the Teide violet dominate. The south, on the leeward side, barely receives the trade wind: there the sea of clouds does not form nor does the laurel forest thrive, and the landscape is arid and sunny.

As an island of persistent volcanism, Tenerife is furrowed by deep, narrow ravines of linear course, very different from the broad valleys of the islands where erosion has worked longer. In Anaga, whose summits exceed 1,000 metres, and in Teno, erosion has carved true canyons such as those of Natero, Masca or El Carrizal, which drain between cliffs of more than 300 metres deserving of the name Los Gigantes. Later eruptions overflowed the northern cliffs of Teno and formed Teno Bajo, a gently sloping "isla baja". Something similar happened in the north: lava flows spilling into the sea from a 70-metre cliff pushed the coastline back some 500 metres along a kilometre and a half, creating the platform occupied today by Puerto de la Cruz.

The great gravitational landslides have also left two almost opposing horseshoe-shaped depressions: the Güímar Valley, opened towards the southeast around a million years ago when the flank of the Pedro Gil stratovolcano collapsed, and the Orotava Valley, formed half a million years later on the northern slope. Both were bounded by nearly vertical walls, with drops of some 300 to 400 metres above the floor, and were resurfaced by later lavas that gave them fertile soils. The Orotava Valley, a depression 10 to 20 kilometres on a side, became one of the most celebrated agrarian districts of the Canaries.

Human geography reproduces this natural architecture. On the Vega of La Laguna, once a lagoon and one of the island's few flat territories, sits the metropolitan area linking Santa Cruz de Tenerife, the capital, with San Cristóbal de La Laguna; the northern midlands concentrate traditional agriculture, today partly replaced by greenhouses, while the leeward coast hosts contemporary tourist development. Water has always been the key: decisive already for Guanche settlements, it was later sought through wells dug in the ravine beds and water galleries bored into the island's volcanic depths, a mining of water that sustained valleys, midlands and cities.