The volcanic activity which formed the Canary Islands has created a variety of scenery, from distinctive lava formations to enormous volcanoes crowned by huge, gaping craters. The islands are all at different stages in their evolution. Tenerife, Lanzarote, El Hierro and La Palma are still volcanically active; dramatic displays of flames and steam can be seen in Lanzarote’s Montañas de Fuego. The last eruption was on La Palma in 1971.
The Canaries are situated above faults in the earth’s crust, which is always thinner under the oceans than under the continents. When magma (molten rock) rises through these cracks volcanoes are formed.
Lanzarote, El Hierro and La Palma are wide, gently sloping shield volcanoes standing on the sea floor. All of them are composed of basalt formed by a hot, dense magma. The flexible crust is pressed down by the weight of the islands.
An explosive eruption can empty the magma chamber, leaving the roof unsupported. This collapses under the weight of the volcano above to form a depression, or caldera, such as Las Cañadas on Tenerife. There are thick lava flows during this stage of the island’s evolution.
If eruptions cease a volcano will be eroded by the action of the sea, and by wind and rain. Gran Canaria’s main volcano is in the early stages of erosion, while the volcano on Fuerteventura has already been deeply eroded, exposing chambers of solidified magma.