Gruta do Carvão

Carvão Cave

Useful Information

Location:	Rua do Paim, 2 Circular, 9500-230 Ponta Delgada, São Miguel. At the outskirts of Ponta Delgada, next to the motorway. Motorway R1-1A towards Relva, exit Paim, turn left under the motorway, then right, right again under the motorway, then left. Signposted with brown signs. It only 2 km from the city center (hrabour) so its possible to go the with public transport or by foot. (37.7481640, -25.6870687)
Open:	All year daily 10-12:30, 14-18. Booking recommended. [2024]
Fee:	Adults EUR 9, Children (7-14) EUR 5, Children (0-6) free, Students EUR 7, Seniors (65+) EUR 7, Azores Residents free. Long Tour: Adults EUR 25. [2024]
Classification:	lava tube
Light:	Incandescent
Dimension:	L=1,912 m, T=15 °C. Paím: L=880,2 m. Secadores de Tabaco: L=701,8 m. João do Rego: L=287,4 m. José Bensaude: L=42,7 m.
Guided tours:	Short Visit: L=200 m, D=30-45 min, Max=15. Long Visit: L=1,000 m, D=2-3 h, Max=5, MinAge=10.
Photography:	allowed
Accessibility:	no
Bibliography:	H. Delgado, J. Nunes, C. Gomes, Z. França (2000): Mineralogy and chemistry of a residual soil developed from pumice argillisation, at Gruta do Carvão, Ponta Delgada - Azore, Proceedings da 1st Latin-American Clay Conference - Clays in Volcanic Environments, Funchal, Vol II; 383-385. J. C. Nunes, T. Bragaej, P. Constância (2002): Carvão cave (S. Miguel island, Azores, Portugal): an educational experience, Abstracts - Xth International Symposium on Volcanospeleology. Setembro. Reykjavik. Islândia; p. 28.
Address:	Reservations: Tel: +351-296-284155, Cell: +351-96-139-70-80. E-mail: Amigos dos Açores, Associação Ecológica, Sede da Junta de Freguesia do Pico da Pedra, Avenida da Paz, 14, 9600-053 Pico da Pedra, Tel: +351-296-498004, Fax: +351-296-498004. E-mail:
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then. Please check rates and details directly with the companies in question if you need more recent info.

History

16th century	first mentioned by the historian Gaspar Frutuoso in his IVth book named Saudades da Terra.
1821	John White Webster mentions the existence of a cave in Arrifes, which was a nowadays inaccessible prolongation of Gruta do Carvão.
1860	George Hartung describes a visit of the cave.
1881	Ernesto do Canto describes a visit to the Secadores de Tabaco section.
1881	William Halliday, member of the Western Speleological Survey, U.S.A., describes the Gruta do Carvão one year after his visit.
1886	Walter Frederic Walker, member of the Royal Geographical Society, describes the cave in his book The Azores or Western Islands.
1984	Associação Ecológica Amigos dos Açores founded.
1988	first cave tours of the Associação Ecológica Amigos dos Açores.
1991	Speleology Working Group created.
1994	Amigos dos Açores prepare a “Proposal for Museological Intervention in Gruta do Carvão”.
11-MAY-2005	declared a Regional Natural Monument by the Government of the Azores by the Regional Decree Nº4/2005/A.
APR-2007	show cave opened to the public.

Description

The Gruta do Carvão lies beneath the streets and buildings of the western outskirts of Ponta Delgada city. There is another cave with a similar name, called Showcave Algar do Carvão on Region Ilha Terceira. The explanation is easy, Carvão means coal in English, and refers to the black colour of the cave walls. Most of the caves on the islands are lava tubes, and lava very often has this dark black colour. As a result there are various "Coal Pits". Of course, there is no coal found on these islands.

Very astonishing is the fact that this volcanic cave contains amorphous silica stalactites, which turn some parts of the ceiling orange. They were formed by silica, dissolved by the water from the lava, not by calcite as in karst caves. The colour is the result of the iron oxides limonite and hematite. This is really exceptional, and the result of a special chemistry of the lava. Quite normal, but still very impressive, are lava stalactites, stalagmites and other lava formations like lava balls, which were formed by flowing lava, which then solidified when it cooled down. Lava bridges link walls, and balconies run along the walls, both were formed on the surface of the lava flow, which cooled first and thus created horizontal plates and ledges. They are a kind of watermark, evidence of a certain level of lava in the tunnel. There are also extraordinary multicoloured rock formations with weird shapes which are the result of lava remains cooling down in the tube.

The cave extended originally from the Serra Gorda volcano, where the lava erupted, over a distance of 5 km southward to the coast of Santa Clara in Ponta Delgada, where the lava flowed into the sea. This area is the Complexo Vulcânico dos Picos (volcanic complex of Picos), an area with around 250 volcanic cones, which is about 50,000 years old. The eruption which formed the cave happened between 5,000 and 12,000 years ago. Over time, the ceiling of the tube started to collapse, and so there are now numerous sections, which are not connected any more. About 1,912 m of lava tube are known, which form four main sections, Paím, Secadores de Tabaco, João do Rego, and José Bensaude. The show cave is located in the Paím section. The Secadores de Tabaco (Tobacco Dryers) is also known as Rua de Lisboa, and as the road had a different name, then it was known as Gruta da Rua Formosa in the 19th century. In this road was the Fábrica de Tabaco Micaelense, a tobacco dryer, hence the other name. Some parts of Gruta do Carvão were discovered by locals doing work in their gardens. Other sections were found during the construction of Ponta Delgada’s airport.

There are some historic records which state that the cave was once 5 km long. The distance between the Serra Gorda vent and the coast is 5.3 km, a 5 km long lava tube is obviously possible. The remaining tubes are only sections of this original tube. Nevertheless, it's a little strange that so much of the cave still existed a few hundred years ago but is now completely destroyed. Weathering of lava tubes is fast, but it's still a geological process, and a few centuries typically make no big difference.

The cave is long known, and actually it is unknown when it was discovered. It was first mentioned in the 16th century by the historian Gaspar Frutuoso in his IVth book named Saudades da Terra, referring to the existence of volcanic tunnels west of Ponta Delgada. It was mentioned by several physicists and geologists during the 19th and 20th century. Gruta do Carvão was considered as the most remarkable volcanic tunnel of the Azores. Beneath the scientific exploration, the cave was also examined as an air raid shelter during World War II, and it was used for some time as a storage place by the nearby Tobacco factory. As a result, one entrance behind a factory has a flight of stairs which are lit by a string of light bulbs leading to a roomy passage. The passage ends where a large stormwater drain broke into the cave ceiling. Even before the cave was developed, many people visited this section, due to the entrance staircase and the huge passage it was easy to visit. In a few years, 1,441 school children have visited the cave as part of an environmental education program.

The development as a show cave took quite long, as the cave was used for a long time for trash, especially at the entrances. The ecological association Amigos dos Açores began in 1994 with exploration and cleanup. From 1995 to 2006, they removed 22 tons of soil, trash and debris. The cave and the surrounding area were declared a Regional Natural Monument by the Government of the Azores in the same year. The show cave was finally opened to the public in April 2007.

There are two guided tours which are called the Short Visit and the Long Visit. The Short Visit explores 200 m of the cave and takes about 40 minutes. Halfway is a skylight, a natural opening in the ceiling that allows sunlight to enter. This is the normal guided tour with trails and electric light. Although helmets are unnecessary for this tour, visitors get one, probably to make it more interesting. And it's easier to recognize the guide, who has a red helmet while guests have blue helmets. The Long Visit is a cave trekking tour through 800 m of undeveloped lava tube. Participants are equipped with a helmet, headlight, gloves and knee pads.

Like any cave, Gruta do Carvão is home to multiple forms of life. Birds like passers, common blackbirds, and common chaffinches visit the cave at night, sometimes rabbits fall into cave openings and are not able to leave the cave any more. True cave dwellers are arthropods (invertebrates) with species like Chthonius ischnocheles, Eidmanella pallida and others. Plants enter the cave with their roots from the surface, because the cave has a high humidity. Around the entrances Macaronesian holly, Azores laurel, and many ferns grow.