Caldeira da Graciosa
Classified as a Natural Monument in 2008, the Caldeira da Graciosa has 119.87 hectares and corresponds to an oval volcanic depression area localized on the southeast part of the island.
The caldera formed about 12 thousand years ago high-interest geological structure with several types of volcanic formations, such as the various lava tubes, of which Furna da Maria Encantada and Furna do Calcinhas stand out, two small hydromagmatic cones and a marshy area. However, Furna do Enxofre stands out from the other formations as a valuable landmark of the island's geodiversity, which is one of the most remarkable volcanic cavities in the Archipelago and unique in the international panorama. It is also rich in biodiversity, hosting several endemic flora and fauna species.
Caldeira da Graciosa is a collapse caldera of elliptical shape, with an area of 120 hectares and a depth of 270 metres, being the second largest forest and the highest elevation of Graciosa with 405 metres.
The origin of Furna do Enxofre is associated with the formation of a lava lake inside the caldera, which overflowed to the northwest, originating other caves, such as Furna da Maria Encantada. Furna do Enxofre also has a cold-water lagoon and a fumarolic field, with carbon dioxide emissions and a mud fumarole. It has an arched roof, with a maximum length of 194 metres and about 50 metres of height in the central area.
The caldera’s interior has abrupt walls, only softened at the bottom due to the slope deposits covered by endemic vegetation such as Azorean Tree Heath (Erica azorica), Macaronesian Laurel (Laurus azorica) and Hypericum foliosum, by the autochthonous Fire Tree (Morella faya) and mainly by the introduced species Japanese Cedar (Cryptomeria japonica) and Australian Blackwood (Acacia melanoxylon).
In this habitat lives the only native mammal species of the Azores, the Azorean Bat (Nyctalus azoreum), and endemic passerine subspecies, such as the Azores Chaffinch (Fringilla coelebs moreletti), the Sylvia atricapilla atlantis, the Azores Grey Wagtail (Motacilla cinerea patriciae), the Azores Blackbird (Turdus merula azorensis) and the Azores Common Starling (Sturnus vulgaris granti), as well as other important endemic subspecies as the Azores Woodpigeon (Columba palumbus azorica) and the Buzzard (Buteo buteo rothschildi). It is also one of the few places on Graciosa where it is possible to observe the waders Common Snipe (Gallinago gallinago) and Wookcock (Scolopax rusticola).
This protected area is classified as Wetland of International Importance by the Ramsar Convention (Ramsar Site) and Nucleus Zone of the Biosphere Reserve and constitutes the Caldeira and Furna do Enxofre priority geosite of the Azores UNESCO Global Geopark.