This cavity is a swallow-river that receives the waters of the Riosu Longufresu, which after two jumps (of about 15 and 25 meters) and a short underground path, flow out, flowing into those of the Riu Semuccu.
The Rio Longufresu, is formed thanks to the union of two channels coming from the mountains of Seui, the first, the Rio su Turnu, flows in the deep gully that develops between the northern slope of the forest of Margiani Ghiani and the southern slope of Genn’Erui, forming along the way eddies and waterfalls; the second, the Rio su Longufresu wedges into a high rock wall giving rise to the important waterfall of about 8 meters called precisely Su Stampu de su Turnu or Turrunu.
The latter, which can be reached by means of an impervious path through the forest of Margiani Ghiani, with LR 31/89, has been identified as an area of relevant naturalistic interest as it represents an interesting karst phenomenon typical of rocks with a calcareous structure.
