[2] Chaco itself is 5,145 metres (16,880 ft)[3] or 5,045 metres (16,552 ft) high and consists of two overlapping volcanic cones, which further have been cut by about three separate sector collapses.
[2] The sector collapses have given rise to avalanche deposits, the largest of which has a volume of about 2.45 cubic kilometres (0.59 cu mi).
[3] Chaco has principally erupted andesite,[2] which contains hornblende, orthopyroxene and plagioclase, but also biotite within lava dome forming andesites.
Some hydrothermal alteration has taken place in the central part of the volcano.
[5] Radiometric dating has yielded ages of 17.0 - 15.5 million years ago.