For decades, most geologists have assumed that the Canary Islands were formed like Hawaii, by the effect of a hotspot in the Earth's crust that pumps magma towards the surface and builds huge volcanic islands as the ocean floor moves over it.
However, the geological process that made the Canary archipelago emerge from the bottom of the Atlantic over millions of years of eruptions, with its islands and numerous seamounts, may have nothing to do with the one that built the Pacific islands, but depends directly on tectonic dynamics connected to the neighboring Atlas Mountains in Morocco.
This is what five researchers from the Complutense University of Madrid, the University of La Laguna, and the Geological and Mining Institute of Spain (IGME-CSIC) propose this month in the journal Earth Sciences Reviews, in a work that challenges the consolidated theory of the hotspot and the volcanic plume as the driving force behind the Canary Islands.
The proponents of this theory maintain that there is a hotspot in the crust located at the eastern end of the Canary Islands that has been raising the islands over millions of years as the ocean floor moves in a west-east direction.
This, in principle, agrees with the fact that the youngest islands of the archipelago, El Hierro and La Palma, which emerged from the sea 1.12 and 1.79 million years ago, are right in that place, and the geologically oldest and most eroded ones, Lanzarote and Fuerteventura, which did so 15.2 and 22 million years ago, are much further east, already off the coast of Africa.
Its signatories, Francisco Anguita, Carlos Fernández, Álvaro Márquez, Ricardo León, and Ramón Casillas, argue that, beyond the similarities between Hawaii and the Canary Islands as volcanic islands emerged from the ocean, the hotspot thesis has many weaknesses.
The first of these, they point out, is that at least three scientific studies have been unable to detect the conduits through which magma from the mantle would constantly ascend towards the ocean floor beneath the Canary Islands, not even in the first 1,000 kilometers of depth. Only one from 2015 speaks of the existence of this type of conduit, but it has not been possible to replicate it, they emphasize.
The second lies in the fact that the Canary Islands and Hawaii are less alike than is usually assumed. For example, the periods of uninterrupted volcanic activity have been very long in the Canary Islands (18 million years in Fuerteventura, 15 million in Lanzarote, 12 million in Tenerife, and 11 million in La Gomera), while in Hawaii the longest has not reached 6 million years (Kauai).
Another difference questions the hotspot thesis: in theory, only the island located directly above should be active, as is the case with the largest island of Hawaii and its neighbor Maui. However, all the islands of the Canary Islands have had episodes of volcanism in the last million years, with the exception of La Gomera, whose last volcanic activity dates back 1.9 million years.
The authors also warn of another problem that challenges the hotspot model that supposedly builds the islands as the ocean floor moves towards Africa: Tenerife, located in the center of the archipelago, and Lanzarote, located to the east, at the theoretically farthest point from the volcanic plume, have suffered repeated eruptions in historical times.
And, finally, they emphasize that the islands of Hawaii are slowly sinking into the ocean as they move away from the hotspot, to the point that they are destined to become seamounts in the distant future.
In contrast, in the Canary Islands, there are islands where the land has risen up to 3,000 meters from the volcanic bed after having passed over the theoretical hotspot that formed them. And not only have they been raised: some have rotated their position up to 90 degrees.
This work argues that in the Canary Islands there are several tectonic structures that connect its geological activity with the displacement of the Nubian plate since the Oligocene (in the last 34 million years) and with the dynamics that are also observed in the Atlas.
"We have been able to construct an alternative hypothesis centered on the regional weakening of the lithosphere, that is, a hypothesis based on the plate. The similarity of the geological, geophysical, and geochemical characteristics between the islands and the neighboring Atlas Mountains offers a relevant common solution in the new hypothesis, which has also allowed the integration of both areas in the evolutionary history of the Nubian plate," the authors conclude.
