It is the largest known Quaternary silicic volcano body and part of the most recent phase of activity in the Altiplano–Puna volcanic complex.

Three large lobate lava flows erupted in the col between two volcanoes and advanced for a maximum length of 14 kilometres (8.7 mi).

The eruption that originated the lava flows probably lasted more than one hundred years and occurred before the Holocene.

[1] The region is dominated by the Altiplano–Puna volcanic complex, where during the Miocene–Pleistocene epoch large ignimbrite eruptions occurred.

The eruption forming the flow may have been caused by the injection of andesite in a pre-existent homogenous dacitic magma chamber.

It has a volume of 26 cubic kilometres (6.2 cu mi) and its flow front is 400 metres (1,300 ft) high.

Based on volumetric considerations, the eruption lasted about 100-150 years with an average lava flux rate of 25 cubic metres per second (880 cu ft/s).

Most of it is buried beneath the flow and only on the eastern side does some material emerge; its volume is estimated at 1 cubic kilometre (0.24 cu mi).

[1] An overlapping pair of pyroclastic cones sits on top of the Chao flow and form its eruption vent.

The cone has a dense rock equivalent volume of 0.5 cubic kilometres (0.12 cu mi) of lapilli and blocks.

They have a combined volume exceeding 22 cubic kilometres (5.3 cu mi) and are formed from a long southbound flow with some lateral spillage.

The lava has a porphyric texture owing to its high crystal content of 45% and displays extensive flow banding.

However, anomalous chemical compositions of the dated rocks suggest that they may overestimate the true age of the volcanics.

A glacial moraine system lies on Cerro del León at 4,500 metres (14,800 ft) altitude.