The Canary Islands

The archipelago of the Canary Islands is located between latitudes 29º 24’ 40ˮ N of Punta Mosegos (Alegranza) and 27º 38’ 16ˮ N of Punta de los Saltos (El Hierro) and between longitudes 13º 19’ 54ˮ W of La Baja (Roque del Este) and 18º 09’ 38ˮ W of Roque del Guincho (El Hierro). The archipelago is made up of seven larger (Tenerife, La Palma, La Gomera, El Hierro, Gran Canaria, Lanzarote and Fuerteventura) and much smaller islands (Alegranza, La Graciosa, Montaña Clara, Lobos, Roque del Este and Roque del Oeste). The lighthouse at La Entallada in Fuerteventura is less than 100 km from Cape Juby on the nearby African coast. The total area of the Canary Islands is 7,447 km2 and the total length of the coastline is 1,583 km. The highest point is Mt Teide in Tenerife and, at 3,718 m asl, it is also the highest in all Macaronesia.

The eastern islands of Lanzarote and Fuerteventura are the oldest, emerging around 16-22 million years ago (Ma), followed by the central islands of Gran Canaria, Tenerife and La Gomera, aged roughly between 8.5 and 14.5 Ma. La Palma is the oldest, at around 2 Ma, and El Hierro the youngest (1.1 Ma). The most recent submarine volcanic activity in the Canary Islands occurred in October 2011, just 2.5 km south of El Hierro. The eastern islands are the oldest and are therefore heavily eroded, with great expanses of undulating terrain composed of materials from old volcanic edifices. The central islands are extremely mountainous with many valleys and deep ravines. The westernmost islands are dotted with hundreds of recent volcanic cones, evidence that these islands are still under construction.

The subtropical maritime climate of the Canaries is influenced by the trade winds and the Gulf Stream in much the same as the other archipelagos of Macaronesia. The trade winds originate at higher latitudes and transport masses of cool damp air. A sea of clouds is formed when these air masses collide with the slopes of the most mountainous islands. As it passes through the Canaries, the Gulf Stream transports cold surface waters, thereby protecting the islands from the influence of the Sahara, the world’s largest desert.

Geologically, the Canaries are made up of a series of independent volcanic elevations (except for Lanzarote and Fuerteventura that form a single island block separated by La Bocaina Strait), which emerge from the ocean floor at more than 4,000 m depth. The islands are situated in an ocean-continent transition zone, over the oceanic crust whose age varies from 150 to 180 Ma (millions of years) and corresponds to the early stages of the opening of the Atlantic Ocean. Apart from the islands, there are several seamounts in the surrounding area, including those of La Concepción and Dacia, to the north of Lanzarote, and Amancay, between Gran Canaria and Fuerteventura.

The origin of the islands is still very much the subject of debate, but essentially there are three main hypotheses that have offered different explanations to how the archipelago was formed. The first points to a hot spot, a mantle plume beneath the earth’s crust and the source of all the magmas that formed the archipelago. Since this hotspot is in a fixed location in relation to the African tectonic plate, aligned from west to east, a chain of islands would gradually form, the youngest being towards the west. However, this idea is fraught with problems, and another two alternative hypotheses have emerged: the propagating fracture model and the theory of uplifted blocks. The first maintains that the archipelago emerged over the prolongation of a great ENE-WSW fracture, originating from south of the Atlas mountains, whose repeated activity from east to west generated the magmatism that gave rise to the Canary Islands. The second considers that the islands were formed by uplifted blocks, a result of an important system of reverse faults. Latterly, a consensus theory has appeared, based on several points from all three theories.

All the islands in the archipelago passed through similar stages during their formation, which is reflected in a series of stratigraphic volcano units. However, each series evolved at different times on each island and is only observable on three. These units are as follows: the basal complex and subaerial volcanism. The only visible basal complexes are in Fuerteventura (Betancuria massif), La Gomera (Vallehermoso caldera) and La Palma (Taburiente caldera). Basal complexes, where visible, are the oldest units of the islands. In Fuerteventura, the basal complex began to form on the ocean floor of the future island around 70 million years ago (Ma), a process that continued for 45 Ma until the final manifestations occurred around 25 Ma. In La Gomera, the unit evolved between 25 and 19 Ma and in La Palma, around 4 Ma. A common feature of basal complexes is that they are made up of plutonic rocks, submarine lavas, sediments and dense dike swarms. Subaerial volcanism developed after the submarine stage that led to the emergent areas of the islands. The second stratigraphic volcano unit gradually evolved thereafter, beginning with the shield-building stage around 20 to 15 Ma in the eastern islands and 2 Ma in La Palma and El Hierro. The remains of these shield volcanoes are the old basaltic series or tubular basalts from the Older Series. There then followed two volcanic cycles, known in the literature as the Intermediate and Younger Series, the latter culminating in the historical eruptions of the last 500 years. From a geochemical perspective, the volcanic rocks of the Canaries belong to the alkaline igneous suite, which is formed by a sequence of rocks whose composition evolves from under-saturated (represented by basalts) through intermediate (represented by trachybasalts) and finally to saturated or evolved forms (represented by trachytes and phonolites). Generally speaking, in the Canaries there are three types of materials with well-differentiated mechanical behaviours: 1) deposits of pyroclastic rain or ash, unwelded ignimbrites, pyroclastic surges, breccias and cinerites, 2) basaltic, trachytic and phonolitic lava flows, welded ignimbrites and autobrecciation, and 3) sedimentary formations. Pyroclastic materials (lapilli and scoria) are very common on all the Canary Islands and appear as small volcanic cones. Ignimbrites are unwelded and found most commonly on Tenerife and Gran Canaria in the shape of thick blocks (1-5 m). Basaltic lava flows are common throughout the archipelago, but Gran Canaria and Tenerife have the largest concentrations of trachytic and phonolitic lava flows. Finally, sedimentary formations are associated with intensely erosive processes, such as the debris avalanche deposits along the north coast of Anaga (Tenerife), or with arid periods accompanied by strong winds, such as the eolian sand deposits that cover many areas of Lanzarote and Fuerteventura.

The oldest known vertebrate fossils in the Canaries belong to the giant tortoise of the Mio-Pliocene and Pleistocene, and to large birds from the Miocene located inside tuff (pumice) and in calcarenites (consolidated sand) at the Famara massif in Lanzarote. However, some controversy surrounds the exact assignation of the Famara birds, although recent studies show that the fossilized eggs are ostrich eggs. The remains of a snake from the family Boidae, until recently the only fossils from this group, have also been found among these deposits at Famara. However, an articulated axial skeleton of another species of snake has lately been found in Fuerteventura. The tortoises, of the genus Geochelone, are similar to others currently living on other oceanic islands and were once widespread in the Canaries. Remains have been found in Tenerife (G. burchardi), Gran Canaria (G. vulcanica), Fuerteventura and Lanzarote (Geochelone sp. 1 and sp. 2). These tortoises are the only example of gigantism among the species of Canary Island fauna. The absence of predators and abundant food resources are factors that favour evolutionary trends towards increasing body size of species living on islands.

Volcanic tunnels are a natural trap that preserve the fossils of birds, mammals and reptiles from long ago. As a result, they are one of the main sources of paleontological data on volcanic ecosystems. Most of the Canary Islands extinct species of vertebrates have been found inside such tunnels. This is true for the giant Canary Island lizard (Gallotia goliath) in Tenerife, La Palma, La Gomera and El Hierro, for the Tenerife giant rat (Canariomys bravoi) and the lava mouse (Malpaisomys insularis) in Fuerteventura, and for several species of birds (Puffinus olsoni, Coturnix gomerae and various Passeriforme birds). The arrival of invasive species, such as rats and cats, must have drastically affected island species and led to their extinction through predation and disease transmission. These species would also have been an efficient source of protein for the original settlers, as testified by remains found at archaeological sites.

Sand dunes are one of the most important terrestrial sedimentary deposits for paleontological research in the Canaries. They act as a kind of cemetery for both vertebrate and invertebrate fauna, preserving their remains by swiftly burying them in an arid environment. Some fossilized species of terrestrial gastropods new to science have appeared in blocks of consolidated sand from the Mio-Pliocene, such as the four species of the genus Canariella, in Gran Canaria, and from the Pleistocene, Napaeus lajaensis, in Tenerife. Fossilized dune formations also throw up the so-called Anthophora nests, which belong to different families of coleopterans and hymenopterans. These tiny thimble-shaped structures are really insect tracks.

Finally, terrestrial fossils include plants, a very rare group in the Canaries due to the volcanic nature of the islands, which does not favour their formation. Nevertheless, trunks, leaves, fruits and other plant remains occasionally appear among volcanic materials (Gran Canaria and Tenerife).

The marine fossil record reveals that the oldest known fossils in the Canaries are found in the basal complex of materials in Fuerteventura, represented by fossilized algae, pelagic bivalves, echinoderms and foraminiferans, such as specimens of Partschiceras cf. whiteavesi, a cephalopod belonging to the legendary group of ammonites that dominated the seas in the Mesozoic era (between 250 and 65 Ma). In the Canaries, numerous paleontological sites, known as raised beaches, resulted from changes in sea level (eustatic movements) and date from the Pliocene and Pleistocene. These deposits contain fossilized molluscs and calcareous algae belonging to different species, depending on the environmental conditions that prevailed at the time. The oldest sites are generally located a few metres above current sea level, sometimes up to 120 m. Conversely, sites corresponding to the Quaternary are usually found from 1-4 m asl.