Monumento Natural Regional do Algar do Carvão
Previously forming part of a Natural Geological Reserve, the area of Algar do Carvão (roughly 40.5 hectares) was recently reclassified as a "Regional Natural Monument" because of its volcanic peculiarities and its importance in environmental terms.
The mouth of the cave (17m x 27m) opens onto a vertical channel with a drop of roughly 45 metres. After a ramp, formed by a gravitational deposit, there is another vertical drop ending in a lake of clear water, at a depth of roughly 80 metres. The lake is fed by rainwater and has a maximum depth of roughly 15 metres, being almost completely dry in the summer in those years when there is little rainfall.
The complex geological and biochemical phenomena occurring in the hydrogeological system that characterises Algar do Carvão have led over the years to the formation of exuberant and rare stalactites and stalagmites of amorphous silica, which are amongst the most beautiful in this cave and in the various volcanic cavities of the Azores.