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El Teide vents hot gases and steam from fumaroles; this one is very close to the summit (Walks 37–40)

The African landmass is the visible part of a continental plate that extends into the Atlantic Ocean, but the Canary Islands lie within the oceanic crust of the eastern Atlantic Ocean, close to the passive junction with the African continental plate. It is thought that the islands now lie directly above a hot-spot, or mantle plume, some 2500km (1550 miles) deep within the Earth. The mantle plume is fixed, but the oceanic and African plates are drifting very slowly eastwards. Every so often a split in the oceanic crust opens above the mantle plume, allowing molten rock to vent onto the ocean floor. As more and more material erupts, it piles higher and higher until it rises from the sea. Each of the Canary Islands was formed this way.

Lanzarote and Fuerteventura were the first Canary Islands to form, and were subsequently pulled eastwards. The next time a rift opened over the mantle plume the islands of Gran Canaria and Tenerife were formed, and these were in turn pulled eastwards. A further oceanic rift led to the formation of La Gomera, La Palma and El Hierro. Looking forward in geological time more islands will appear as other rifts are torn open in the future.