Algar de Carvau is a volcanic chimney with a depth of 90 meters, formed on the island of Terceira approximately 3,200 years ago after the deposition of magma from the main chimney to the magma chamber by a volcanic eruption. It is considered one of the most attractive geological features in the Azores. Of the many caves that have a distinct group of stalagmites and stalactites formed from deposits of silicic acid, which is unusual in this region.