Del. Ukk.22 Tobozo

The pit develops through a series of narrow verticals, among them a shaft of 115 metres, and reaches -445 metres. At that depth an active gallery is reached which, downstream, splits into two branches: one ends at -470 metres and the other at -512 metres in a sump. Upstream, a succession of galleries and large chambers leads to some active laminators and galleries that advance toward the eastern limit of the massif, in the direction of other explored cavities; the ascending drop of this part, from the base of the shafts, exceeds 300 metres. The cavity has a depth of -522 metres and an approximate length of 7.5 kilometres.

At -445 metres an active gallery is reached; downstream, one of its two branches ends at -512 metres in a sump. Upstream, a succession of galleries and large chambers leads to some active laminators, very dangerous in the event of a flood.

In 1986 the Belgians of the Centre Routier Spéléo (Bruxelles) locate the entrance and begin the exploration of the pit, through a series of narrow verticals that gave rise to a series of diggings; such verticals include a shaft of 115 metres, reaching -445 metres.

In 1986 the Grupo Espeleológico Centre Routier de Bruselas (Belgium) locates the aforementioned cavity (UKK.22.- Sima del Río de Ukerdi). Without a doubt this is another important cavity within speleology in the Comunidad Foral de Navarra.