This volcanic island was formed about 20 to 12 million years ago, raising from the 5,500 m deep ocean floor. The last eruptions happened in prehistoric times. Erosion is very intensive, and so the whole island is very steep, with few narrow and deep valleys. This deep ravines run from the center radial to the sea.
Geologic sights of the island are pillow lava at the coast of Arguamul, and the basaltic columns at Los Organos. The biologic sight of the island is the forest at Garajonay National Park in the center, with an exceptional laurasilva forest or better a brushwood of laurel, spurges, and thistles. This place is designated a World Heritage Site by UNESCO.