Cerro Chascon is located within the moat of the Pastos Grandes caldera (q.v.), immediately to the west of Laguna Khara (K). Cerro Chascon is a torta with its vent located roughly in the geometric centre of the body, and it is part of a remarkable chain of small rhyodacitic lava bodies (Cerro Runtu Jarita) extruded from a fissure, which probably form the surface expression of a subsurface dike similar to that described connecting the Inyo domes, California (Fink and Pollard, 1985). The eruptions of all of the domes and flows in the area seem to have been triggered by mafic recharge (Watts et al., 1999). The Cerro Chascon lava is unusually crystalline (45-48%) with 68-76% SiO2. Evidence of initial explosive activity as the magma is preserved in a small local rhyolitic airfall. Watts et al. (1999) believe this to primarily consist of a non-volatile driven eruption of juvenile material. A small tuff-ring was created by an initial phreatic eruption that opened the conduit for this explosive eruption.
Fink, J.H. and Pollard, D.D. 1985. Geometry of silicic dyke beneath the Inyo Domes, California. J. Geophys. Res. 90, p11127-11133.
Watts, R.B., de Silva, S.L., Jimenez de Rios, G., and Croudace, I., 1999. Effusive eruption of viscous silicic magma triggered and driven by recharge: a case study of the Cerro Chascon-Runtu Jarita Dome Complex in Southwest Bolivia. Bulletin of Volcanology, 61(4):241-264.