Bonozorrotz I

The entrance has been opened artificially, due to the working of a quarry for the extraction of limestone, which is now abandoned. The galleries have a changing morphology, with phreatic types predominating, with very intense cavitational marks. In some areas two different moments in the evolution of the cavity can be clearly seen. The first shows great physical as well as chemical wear, which develops from two main contraction joints, which are interconnected by several transverse fractures. These lithoclases develop along a predominant direction of about 42°/222°. Subsequently a second morphology develops, when a strong chemical dissolution of the limestone begins, coating the entire cavity with irregular flowstone, completely changing its appearance. Clastic deposits are not abundant, since the cavity was created practically by physical and chemical wear, with the exception of the Ariste chamber, created by gravitational collapse.

Chemical deposits are abundant throughout the cavity, as are those of detrital origin, normally hidden by the former. Flowstone abounds, covering almost the entire cavity. Lithogenic formations are also important, some of them recrystallized.

In some areas where clayey deposits are abundant, it can be clearly seen how, after the fossilization of some galleries, a second rise in the hydrological level occurred, which has re-excavated a central groove by dissolution and instinctive dragging, leaving small detrital terraces at the sides, later covered by a thin calcareous crust.