Aguas Calientes (volcano)
The volcano has been affected by glaciation. Glacial U-shaped valleys are found on the northern and western flanks, giving the volcano some angular patterns. One valley with glacial features and a subglacial river channel at 4,650 metres (15,260 ft) altitude is found on the northern flank. It extends down to the valley north of Aguas Calientes and intersects the youngest lavas of the volcano.
Aguas Calientes has a well formed summit crater. A small crater lake is found within the Aguas Calientes summit crater, making it one of the highest lakes in the world at an altitude of 5,870 metres (19,260 ft). The lake has a surface area of 2,500 square metres (27,000 sq ft) and is tinged red from a population of microorganisms. The lake water is acidic and is frequently influenced by activity from Lascar, with winds carrying sulfuric acid and water vapour clouds to the crater lake. Precipitation was measured at 146 millimetres per year (5.7 in/year) with most precipitation falling during the winter months, and strong UV irradiation. The lake has a bacterial ecosystem that is primarily reliant on photosynthesis but may also be influenced by hydrothermal activity from Aguas Calientes volcano. Research has found only limited numbers of bacterial taxa and a large number of DNA sequences that cannot be identified as known phylogenetic groups. The lake has been studied as a possible terrestrial analogy to Mars.