Volcanic pits like Furna do Enxofre are mostly ancient vertical volcanic conduits that have been lava drained as a consequence of the arise of a new vent/eruptive center at a lower level or the decrease of lava emissions from depth leading to a lateral and/or in depth drainage of magma and the partial emptiness of the feeding conduits. As the eruption ends there is the cooling and solidification of the conduits and there might be some collapses from the walls, increasing pit´s dimensions and creating gravity deposits at the bottom of the pit.
The Caldera of Graciosa is a collapse depression in the top of the polygenetic volcano which is in the southeast area of the island. Inside are two small cones hidromagmatics, a swampy area and a cavity volcanic Furna do Enxofre . This volcanic pit has a vaulted ceiling, maximum length of 194 meters about 40 meters high and also comprehends a fumarolic field geyser of mud that diffuses gas emanations.
The most important part of Furna do Enxofre is located in the SE part of Caldera of Graciosa, and communicates with the outside through two openings arranged along a general northwest-southeast direction. Access to the interior of this cave is by a tower with some stonework and masonry with 37 meters in height that contains a spiral staircase which was built in the early twentieth century.
The exploration of this volcanic pit began in the nineteenth century by several investigators including Prince Albert of Monaco.
This cave is considered unique in the international field and volcanic-speleological, its genesis is associated with an important phase intra caldera effusive, like Hawaii, which involved the formation of a lava lake.
In the final phase of Hawaiian eruptions, the lava on the inside of the boiler, still fluid was drained along the main line of the volcano, precisely the area where this cavity is located.
Inside the Furna do Enxofre, is an important field of gases release, formed by geysers, mud and diffuse gas emanations of carbon dioxide. These gases are released often seamlessly in various areas of the cave floor
About the cache:
50 steps starting from the bottom (then on the right)
136 steps starting from the top (then on the left)
Highly camouflaged
Attention to cache size...