Llullaillaco, Stratovolcano at Chile-Argentina border

Llullaillaco is a stratovolcano on the border between Chile and Argentina that rises to 6739 meters (22109 feet) in the Andes. The mountain flanks show distinct layers of solidified lava and volcanic ash, while the summit area is covered with ice and snowfields.

Llullaillaco grew in two Pleistocene stages, Llullaillaco I and II, and its oldest rocks date to about 1.5 million years ago. Roughly 150,000 years ago its southeastern flank collapsed, sending a debris avalanche up to 25 km from the summit. The youngest dated rocks are 930 ± 140 years old, though 19th-century activity has been reported; the first recorded ascent came in 1950.

The name is usually linked to Quechua llulla ("false, deceitful") and yaku ("water"), perhaps because meltwater sinks into the soil instead of feeding streams; a second reading uses llullu, a soft thing that hardens, evoking lava. Inca occupation of the region between 1470 and 1532 CE left a sanctuary on the summit, excavated from 1983 onward.

Several routes lead from the Chilean and Argentine lowlands to the summit and partly follow old Inca paths. Most ascents begin in the dry season between November and March when snow and ice cause the fewest difficulties.

In 1999, archaeologists found three mummified children from Inca times at the summit, exceptionally well preserved by cold and dryness. This discovery made the mountain the highest archaeological site on Earth.