Structure and Evolution
Volcan Aguas Calientes is a symmetrical cone with a circular basal plan ~7km in diameter which provides an elegant backdrop to Laguna Lejia and its attendant flamingoes (Figure 26.1). Aguas Calientes appears to form part of a short east-west volcanic chain, of which Lascar volcano, 5 km to the west, is the most active member. Short stubby lava flows (i.e. L) in the summit region have resulted in steep slopes of ~45° in the upper parts of the volcano (Figure 26.2; 26.3). The gentler slopes of the lower flanks of the volcano are mantled by fine grained detritus, partly erosional material resulting from freeze-thaw action and partly ash from Lascar volcano (LA). A thin air-fall plinian deposit, visible as a whitish horizon on the TM image (A) appears to be from Lascar rather than Aguas Calientes.
Much of the history of Aguas Calientes is pre-Holocene, since there is little evidence of morphologically youthful lava flows on the lower flanks of the volcano. However, the lava flows in the summit region and a well developed summit crater may have been formed by more recent, probably Holocene activity (Figure 26.3). A shallow crater lake is present within the summit crater, and is apparently unfrozen on the air photograph and TM images. A large arcuate rampart to the north-east of the volcano may be the margin of a débris flow deposit which resulted from failure of the north-eastern part of the ancestral volcano (DFM). In this case Aguas Calientes would have to be re-classified as a composite cone. The several short stubby lava flows rimming the summit region appear to be the youngest activity from the volcano. There have been no records of historic activity.
No activity has been observed in visits to the region from 1983-1989.
The lavas from Aguas Calientes are predominantly porphyritic andesites with dominant plagioclase (An34-42) with either augite and hypersthene, or hornblende and biotite-the proportions of these two groups vary according to rock type. Rare olivine and quartz are also found. Plagioclase in the rocks with olivine have more calcic plagioclases with An45-48 Ramierez and Gardeweg, (1982). Matthews et al. (1994) describes the Aguas Calientes dacitic lavas as containing andesitic mafic inclusions, similar to many nearby volcanoes, which indicate magma mixing processes.
Matthews, S.J., Jones, A.P., and Gardeweg, M.C., 1994. Lascar Volcano, northern Chile; evidence for steady-state disequilibrium. Journal of Petrology, 35(2):401-432.
Ramierez-C.F. and Gardeweg-M. (1982) Hoja Toconao. Carta Geologica de Chile, 54. SNGM, Santiago.