Lanín is the active Andean volcano straddling Argentina and Chile that attracts climbers.
Lanín is a symmetrical, ice-capped stratovolcano rising to about 3,776 metres. It stands on the international boundary in the southern Andes, near Argentina’s Junín de los Andes and Chile’s Araucanía region. The mountain gives its name to Argentina’s Lanín National Park; its Chilean side lies within Villarrica National Park.
Although Lanín has no recorded historical eruption, geological evidence indicates that it has erupted during the Holocene, so volcanologists classify it as active. Its summit is covered by glaciers, and climbing conditions can change rapidly with snow, ice, wind, and weather. The northern route is the standard ascent, while the southern face is more technical and requires greater mountaineering skill.
Osorno and Villarrica are also famous Chilean volcanoes and are common mix-ups. Mount Tronador is a glaciated massif on the Argentina–Chile border, but it is not an active volcano. Lanín is the answer because it combines the border location, active-volcano status, and renowned climbing tradition.