Rock types are made up of phonolite and ignimbrite. The mountainous centre of the island is often covered with clouds, which feed numerous springs, as was already observed by the 19th century traveller Armand d'Avezac.
Rock formations include phonolite and ignimbrite. The mountainous part of the island is frequently covered with clouds that provide water to numerous springs, as was noted by Armand d'Avezac in the 19th century.