Volcán Galán

Volcán Galán in Catamarca Province is one of Earth's largest calderas — 35 kilometres in diameter, visible from satellite images as a near-perfect oval depression in the Puna de Atacama — and it is almost completely unknown outside volcanological literature. The caldera floor sits at 4,500 metres, surrounded by a 500-metre-high rim that has not been breached since the volcano's last major eruption 2.5 million years ago, and the interior contains a salt lake, fumarole fields, and thermal springs visited by perhaps a hundred people a year. The track to the rim requires a four-wheel drive vehicle and a full day to reach from the nearest town.

Galán is a resurgent caldera of the central Andes volcanic zone, formed by a series of catastrophic eruptions over the past 5 million years that deposited ignimbrite sheets across an area of 2,000 square kilometres. The most recent eruption, approximately 2.5 million years ago, is estimated to have expelled 1,000 cubic kilometres of material — making it one of the largest known eruptions in Quaternary geological history. The caldera's interior, accessible only by crossing the rim and descending 500 metres on unmarked terrain, contains Laguna Diamante at 4,700 metres, a hypersaline lake coloured pink by algae and inhabited by James's flamingos at one of their highest known nesting sites. The geothermal activity beneath the caldera floor is still measurable — the springs in the interior reach 80°C.