Gruta do Carvao

The Gruta do Carvao (Grotto of Coal) is an ancient lava tube on the island of So Miguel in the Portuguese archipelago of the Azores, located on the borders of the municipality of Ponta Delgada (in the civil parish of Santa Clara). The Gruta do Carvao was designated as a Regional Natural Monument on May 11, 2005, due to its scientific, educational, and touristic significance, as well as its natural qualities.

The cave is located near the western part of Ponta Delgada and spans for 1,650 meters, making it the largest lava tunnel on the island of So Miguel (5,410 ft). Rua de Lisboa (or Secadores de Tabaco), Rua do Paim, and Rua Joo do Rego are the three portions. Older documentation and field investigations, on the other hand, imply that the tube is actually longer, maybe reaching a length of 5 kilometers (3.1 mi). The part at Rua do Paim is roughly 557 meters (1,827 feet) long, with an internal cavity that is 6.4 meters (21 feet) high and 8 meters (26 feet) wide at its highest extent.

Speleological features such as lateral benches, lava bridges, branching galleries, lava balls, stalactites, stalagmites, columns, spongy lavas, glazing, and tree moulds can be seen along the cavern walls. The walls and ceiling are multi-colored (orange to yellowish) due to basalt oxidization, aside from a few cracks. The walls and ceiling are also covered in conical-shaped stalactites, secondary mineral deposits of silica, and earthen deposits. Many of the stalagmites are 25 centimetres (9.8 in) long and have extensive sections of soda-straw, conical ring-type tubes with pitted pockets overlaid on top.

Length: 1,650 m

Address: R. do Paim, 9500-230 Ponta Delgada, Portugal