Gruta do Carvão (in all its different parts and denominations), has been known for a long time and object of inumerous references by historians and researchers of various subjects.
In the XVIth century, chronicle writer Gaspar Frutuoso, as he was describing Ponta Delgada’s littoral zone in his IVth book in “Saudades da Terra”, refers the existence of volcanic tunnels west of Ponta Delgada: “Ahead, close to Fortaleza (S. Braz), to the west, is a tip called Ponta dos Algares, because two gorges [algares] arise from it, through which one can walk a long way underneath the earth, in a way which seems to be where Ribeira de Pedra de Biscouto ran previously, not known or seen”.
In 1821, John White Webster mentions the existence of a cave in Arrifes, which might correspond to a nowadays inaccessible prolongation of Gruta do Carvão: “Having arrived at a field, three or four miles northwest of Ponta Delgada, we discovered the entrance to the caves, which is a crack in the rocks, a few feet high in this location, wide enough for two people to stand side by side” (...) we fast arrived at a spacious location, whose floor was covered in gigantic lava fragments, fallen from above and making our way difficult and somewhat dangerous”. Webster’s descriptions reveal magnificent details of that volcanic cavity, never after observed and probably lost forever: “(...) from the ceiling lava stalactites were pending, in a very interesting fashion, highly rewarding of the danger and difficulties encountered (...) Where the floor and the ceiling reached one another, one or two feet apart at the end of the cave, where we could distinguish stalactites connecting each other, but nowhere elese have we observed anything similar”.
George Hartung, in 1860, referred to this cave describing its inferior track in the western part of Ponta Delgada: “underground galery (...) to which we descend through an opening at fields in St. Clara, going along 810 feet towards the coast splitting into two halfway”.
Gruta do Carvão was also called Gruta da Rua Formosa, nowadays Rua de Lisboa, where the old Fábrica de Tabaco Micaelense tobacco dryers are located, according to elements provided by Ernesto do Canto in 1881: “In a land in Rua Formosa in Ponta Delgada there is a gorge several kilometers long and really worth visiting”.
Ernesto do Canto describes, in his reports from 1902, the lavic caves’ formation as “underground galleries of variable sizes, produced by lava currents, going down the mountains and running through the fields’ depressions, where they were posteriorly frozen, surrounded by a layer of rock”. As they “conserved themselves liquid in the internal part, they continued running inside this tube structure, which did not condunct heat, until stopping at the origin and continuing the internal mass during the fall, leaving na empty área which constitutes the gorges” [the caves].
Walter Frederic Walker, member of the Royal Geographical Society, the Society of Biblical Archeology and of other scientific associations describes minuciously the cave in his book “The Azores or Western Islands” of 1886: “(...) Next to the entrance, the northern cave, at least 20 feet high and 30 feet wide and fully leveled ground, if explored properly it could probably be discovered that it connects to another gallery, entrance to which is located in a garden belonging to Mrs. Brander, in Foral do Carvão, and would therefore be extended throughout several miles (...). From the ceiling one can see “all sized lava needles, as if a sudden cold gush had cooled the falling incandescent drops”, and provides an explanation for cave formation in volcanic regions according to Sir Charles Lyel’s theory: “were produced by the lava’s hardening during the escape of elastic fluids that are frequently expelled, over a long period after eruption”.
Another traveller registering his impressions on the cave was Emygdio da Silva, in his opuscule “S. Miguel em 1893”, considering the cave as “(...) the most remarkable of the Azores’s volcanic tunnels (…), Ponta Delgada’s tunnel is, from what is known, over one kilometer long and finishes in the ocean after crossing, underground, the alcohol factory of Santa Clara, following a North-South direction (…) 250 or 300 meters from the entrance, in a field in Rua Formosa, property of Mr. Dr. Caetano d'Andrade Albuquerque, the enlargement of this formation is remarkable and as it is located not over 60m of depth, the view from the vast gallery (…) creates an indescribable feeling, even though we had already explored by foot, and also still in construction, several underground structures of relevance”.
In a letter sent to Diário de Notícias de Lisboa towards the end of the XIXth century, Emygdio da Silva reports a visit to Gruta do Carvão accompanied by Coronel Afonso Chaves and lighted by “magnesium’s magic light: the tunnel’s dome, from which thick and black stalactites were falling, the lateral walls covered in highly shaped linings, marking the stops of the lava in its progressive movement, the holes of the small galleries communicating with each other (...) to irregular soil of a vitreous nature, as in Atrio do Cavallo, in Vesuvio, all this is surrounded by magnesium’s astonishing light, constituting one of the most awesome and grandious spectacles Dante would certainly not reject for a scene in his Inferno.”
Manuel Jacinto Andrade, in an article for newspaper Açoriano Oriental reports that “In 1954, from the backyard of a house in Bom Despacho, on the way to Arrifes, workers digging for sanitary purposes revealed, a mere 3 meters deep, a volcanic flagstone which, once battered by a chisel, easily broke. The same worksmen realized the opening led to a cave. Going down those stairs they found an enormous gorge located North-South. It is an enormous underground artery of about 7 meters wide and 4 to 5 meters high, in its highest, with black volcanic material walls and the ceiling full of stalactites. In the North end, 30 to 40 meters from the descent location, a huge square opens up revealing its 20 to 30 meters diameter. To the South, the gorge lowers with practical dimensions, seeming that this way the gallery seems much longer than to the North side. Would this gorge be in anyway related to Gruta do Carvão? It was not possible to find out, as shortly after the owner of the backyard covered this entrance and supposedly used this empty gorge as a water sewage and sanitary disposal structure. Construction works for Nordela’s Airport revealed more gorges in the Northwest region of Ponta Delgada, showing us that in former times, the volcano’s lavas wandered through them opening extensive underground galleries”.
William Halliday, member of the Western Speleological Survey, United States of America, visited the Azores in 1880 and refers to Gruta do Carvão: “(…) besides the lowest part, the cave becomes wider and reveals characteristics of how the lava flew through it (…) with just a bit of work it would be possible to open and make one of the entrances (now closed) wider so that visitor and students could see how their beautiful island was formed (…) I estimate the cave to be 400m long until the final obstruction”. In an essay from 1881, Halliday mentions the existence of a cave whose entrance was located close to the military quarters in Arrifes.