Ollagüe, Stratovolcano in Potosí Department, Bolivia.

Ollagüe is an andesite stratovolcano on the Bolivia–Chile border whose summit reaches 5,868 metres. Its summit crater, about 1,250 metres across, opens to the south, exposing traces of lava, and its western rim is formed by a compound of lava domes. A 100-metre fumarole venting yellow sulphur and white water vapour lies 700 metres west of the crater.

Ollagüe began forming more than one million years ago, building the Vinta Loma and Santa Rosa series of andesitic lava flows. A fault bisects the edifice and triggered two large landslides, one of which collapsed the western flank and split an adjacent salt pan in two. Later activity filled the collapse scar with the Santa Cecilia series, including a lava dome on the western crater rim. No historical eruptions are confirmed, but SERNAGEOMIN monitors the volcano as potentially active.

The Aymara name Ullawi combines ullaña (to see, look at, watch) with the nominalizing suffix -wi, giving "viewpoint". Spanish speakers turned it into Ollagüe, and sources also record the variants Oyague, Ollagua and Oyahué. The Chilean commune and town at the volcano's foot carry the same name.

The climb starts on the Chilean side at the village of Ollagüe, following a track past the old sulfur miners' camps of Santa Cecilia and Santa Rosa at 4,200 m; vehicles stop around 5,000 m, leaving about an hour on foot. Minefields with anti-personnel mines exist in the area, so ask the Carabineros in Ollagüe which zones are dangerous before setting out.

The fumarole on the western crater rim, about 700 metres from the crater, releases yellow sulfur gases and white water vapour; a second fumarole sits on the summit itself. The crater measures 1,250 metres across and its southern part is eroded, exposing traces of lava.