Canary Islands Geology

Geology

     Geologically, the Canary Islands consist of a series of separate volcanic elevations rising from a depth of over 4,000 metres, situated on a transition zone within the oceanic crust, and estimated to be between 150 and 180 million years old, corresponding to the early stages of the opening of the Atlantic Ocean.
     The oldest islands are the eastern ones, Lanzarote and Fuerteventura, which emerged some 16–22 million years ago, followed by the central islands, Gran Canaria, Tenerife and La Gomera, which are between 8.5 and 14.5 million years old. The youngest islands are La Palma, estimated to be around 2 million years old, and El Hierro, around 1.1 million years old. As a result of this significant difference in age, the eastern islands are heavily eroded, featuring vast plains formed by material resulting from the gradual dismantling of ancient volcanic structures. The central islands, where this process has not yet had time to take place, are very mountainous, with an abundance of deep valleys and ravines. On La Palma and El Hierro, their geological youth is clearly evident from the presence of hundreds of volcanic cones, which show that these islands are still actively forming; the clearest evidence of this process is the three volcanoes that have emerged over the last 100 years on the island of La Palma, in 1949, 1971 and 2021.

     There are three main theories regarding their origin, the most widely accepted of which for a long time was the ‘hotspot’ theory, which posits that the Canary Islands have gradually emerged from a thermal plume originating at the base of the Earth’s mantle, which is believed to be the source of all the magma in the archipelago. As this plume is fixed in position relative to the African plate, which is moving from west to east, over time a group of islands would have formed in that same direction.
    However, two alternative hypotheses have emerged in recent times. One is the ‘propagating fracture’ hypothesis, which links the origin of the islands to the successive east-to-west propagation of the Atlas Mountains in North Africa. The other hypothesis—and the one currently most widely accepted within the scientific community—links the origin of each island to reverse faults occurring in the Earth’s crust, resulting in blocks rising from the ocean floor as they collide with the African continent, which in turn leads to a progressive series of magma eruptions.

Volcanology

     Regardless of its origin, the fact remains that the Canary Islands are the result of a succession of volcanic eruptions on the seabed, which have gradually formed each of the islands as the volcanic structure rose above the sea surface. Successive eruptions over thousands or millions of years have built upon one another, so that the islands’ landmass has gradually increased in both area and height.
    Magma can be expelled in three different forms: in a liquid state, as lava flows of varying thickness; in a solid state, as pyroclastic material, lapilli and ash; or in a gaseous state. In the Canary Islands, the first two forms predominate, and they often combine or alternate within a single eruption.
     Pyroclastic materials, such as lapilli or picón, and ash, are very common across all the islands of the Canary Islands archipelago, usually forming small volcanic cones throughout the territory.
    Basaltic lava flows are also very common, and usually produce an extremely rough or even jagged surface, which is locally known as ‘malpaís’. As the lava advances, the scoriaceous surface—which cools as it moves across the ground—collapses at its leading edge, yet continues to advance due to the pressure of the molten lava, which remains hot within the flow.

     Over time, volcanic structures are subjected to erosive processes caused mainly by water, wind and waves, which cause the island’s relief to become progressively smoother and give rise to sedimentary formations, such as the extensive foothill and landslide deposits stretching along the entire northern coastline of Anaga, or the wind-blown sand deposits covering many areas of Lanzarote and Fuerteventura.

Volcanic tubes

     Among the wide variety of volcanic structures in the Canary Islands, the formation of volcanic channels and tubes stands out. These are associated with effusive eruptions and are formed when a lava flow moving down a slope cools on contact with the air, causing both the outermost surface and the area in contact with the ground to begin to solidify, whilst the lava continues to flow between the two solidified layers. If the slope is steep, the lava channel will usually be left empty once volcanic activity ceases, giving rise to the well-known volcanic tubes or caves.
     These magnificent volcanic formations usually remain hidden until, for whatever reason, the upper layer breaks away, forming a ‘jameo’ – that is, a hollow in the ground that exposes the interior of the volcanic tube – as is the case with the Jameos del Agua in Lanzarote. Other examples, renowned for their spectacular nature and length, include the volcanic tubes of the Corona volcano and the Cueva de Los Verdes in Lanzarote, or the Cueva del Viento in Tenerife.

The Story of a Volcano