The volcanic activity of Tenerife during the past three million years has mainly taken place in its central zone, causing an extraordinary growth of the island in height. The observation of the geological processes of Las Cañadas del Teide helped us to understand the geological history of the island. Investigations of the subsoil of the island and studies of the seabed and the submarine relief over the past few years have confirmed the hypothesis upheld by the geologist and geographer tenerife Telesforo Bravo about the formation of Las Cañadas : both the valleys of La Orotava and Güímar, such as La Guancha - Icod (whose head is Las Cañadas) are depressions formed by huge gravitational landslides. This occurred 170,000 years ago, when, due to the instability of its structure, a huge volcanic building slid towards the North of the island.
A great volcanic activity was subsequently triggered and ended up filling the existing cavity. These most recent materials are contained in a large amphitheatre of 17 km in diameter, delimited by the "wall of Las Cañadas", extended along 25 km. In it, it is possible to see dozens of horizontal flows, ashes, dykes and all kinds of volcanic products.
In a first moment, after the slide, there were mainly basaltic eruptions that originated very fluid magmas, with a low content of silica. The fastest lavas are slightly harsh and are called "pahoehoe lava flows", a Hawaiian term that means "lava on which you can walk barefoot". The rough lavas, less fluid, form the badlands and are of type "aa". This term is also of Hawaiian origin and means "lava on which it is very difficult to walk".
As new materials were filling out the original depression, magma found it more difficulty to reach the surface. After intermediate magmas, less fluid than the basalt ones (trachybasalts), in good part expelled by Teide itself, came the more viscous lavas. A higher retention in the ascension creates lavas with a high silica content; those are called trachytes and phonolites. Sometimes, lavas move very slowly, so they solidify while going forward. An example of that is in the large rock blocks of some lava flows.
In the case of phonolite lava, it is not rare to see a type of black rock, of smooth and brilliant surface, called obsidian. This is a volcanic glass, generated during a rapid cooling. Another type of magmas, also of high viscosity but very mixed with gases, are the pumice or plinian eruptions (in memory of the Roman historian Pliny, who described the eruption of Vesuvius that led to the destruction of Pompeii). The materials encountered in this type of volcanism, of extraordinarily explosive character, are called pumice. It is easy to distinguish by its light colour and extremely low weight. This type of volcanism can be observed mainly in Montaña Blanca and in Las Minas de San José.
Without doubt, with its 3,718 m, Teide is the most interesting geological feature in the park. This imposing mountain, together with Pico Viejo, creates a stratovolcano, since they are considered as one volcanic building due to the fact they emerged from the same magma chamber. The last eruption that occurred in the interior of the national park was the one of Las Narices del Teide, in the skirt of Pico Viejo, in 1798.
One of the most characteristic geology phenomena of the park are las cañadas, which give the name to this territory. These are sedimentary plains, usually located at the foot of the walls of the circus and in which materials from the erosion of the escarpments accumulate.
Los Roques de García are also of great uniqueness. These alignments of large rock formations are the remains of an ancient volcanic building, prior to the formation of La Caldera de Las Cañadas. Its current appearance is the result of the erosive action of wind and water.