Urroz I

The entrance is low and leads, via a short and gentle slope of angular cobbles, to a gallery about 2.5 metres high. It widens into some chambers with a large amount of silt deposited on walls and floors. At approximately 100 metres, progress is blocked by a vertical step 1.5 metres deep with large metre-sized clasts at its bottom. After crossing this flooded chamber, one continues with water up to the neck along a vertical joint to a new chamber, where the lake is shallower. Once on the shore, one continues along a gallery of clear phreatic origin, which leads to another chamber with a flooded vertical shaft on one side. The main gallery, along which exploration continues, branches after a few metres into two narrow passages that quickly close the cavity. The development is estimated at about 250 metres. The entire cavity has a clear phreatic origin, with a subsequent evolution of the galleries in vadose form observed.

The detrital deposit conceals a large part of the lithogenic formations and reconstructing processes. Hexagonal crystallization forms have been found, about 12 mm in diameter, which exfoliate very easily into hexagonal plates about 2 mm thick. This crystallization has a very dark red-ochre colour, possibly related to small deposits of iron oxidation; the formation develops in the form of a tube, being very rich in calcium carbonate and very easily scratched.

During the exploration carried out, the vertical step 1.5 metres deep was flooded, forming a lake of great beauty. The floor is completely covered by a very fine greyish silt introduced by the seasonal rises of the Leurza reservoir.

The survey of the cavity could not be carried out due to the rise of the reservoir and its consequent flooding, but an inspection visit could be made.