35) Portillón de Oô

During the Little Ice Age, the Portillón de Oô Glacier, together with the Seil de la Baquo Este and Oeste glaciers, formed a single glacier covering 139 hectares, the largest in the Perdiguero Massif and the third largest in the Pyrenees, surpassed only by the Monte Perdido-Aguas Negras-Pico de Cerro Negro massif. Oeste, formed a single glacier covering an area of 139 ha, the largest in the Perdiguero Massif and the third largest in the Pyrenees, surpassed only by the Monte Perdido-Cilindro de Marboré and Aneto glaciers. Although it did not stand out particularly for its maximum length of 750 m, it did have a wide head, which extended horizontally for 3 km, surpassed only by the Glacier or Monte Perdido.
Photographs from the late 19th century still show a convex ice front in a sector that was later occupied by the Portillón de Oó Glacier. Its split into an independent glacier occurred in the 1930s. In the last third of the 20th century, it represented a glacial relict inserted between the Hito Oeste de Perdiguero (3,176 m) and the Pico Olivier or Portillón de Oô (3,050 m).
In 2017, it already showed a morphology characteristic of heleros, but faint traces of movement were still visible, which ceased to be observed in 2022, when it was classified as a Helero. Since then, its deterioration has progressively worsened to its current size of 0.8 ha.