Cerro Bonete Caldera
Cerro Bonete was first identified by Baker (1981) on Landsat MSS images. Located in a remote part of NW Argentina at the southern limit of the Central Volcanic Zone, it has not apparently been visited by geologists. Consequently what little is known about this interesting structure is drawn from remote sensing studies (Baker, 1981; Francis & de Silva, 1989).
The caldera is ~6 km in diameter, contains a central extrusive lava dome and lake, and is surrounded by a thick ignimbrite sheet, now eroded into small flat topped 'mesetas'. Of particular interest is the ~2 km long lake which occupies the southern part of the caldera. It is impossible to estimate the depth of the lake, but the fact that it is dark in all TM bands suggests that it is probably at least several meters deep and composed of clear water, because shallow lakes and those containing sediments or high mineral concentrations are bright in the shortest wavlength TM bands. In the thermal infrared (TM band 6), the crater lake is distinctly brighter than any of the numerous other small lakes around the caldera. Using established techniques (e.g. Markham & Barker, 1986) the estimated temperature of the caldera lake was found to be ~13ºC which is notably higher than the temperatures of 5-6 °C associated with the other lakes a few kilomtres distant (Francis & de Silva, 1989). While the temperature of the lake is considerably lower than those of crater lakes in active volcanoes such as Poas, Costa Rica (~47ºC; Francis et al., 1980), it is so much warmer than the surrounding lakes that an input of geothermally heated water is probable. An active hydrothermal system is probably associated with the caldera and is most likely to be related to the central dome, which shows evidence of hydrothermal alteration, and may be responsible for weak warm springs feeding the lake.
Baker, M.C.W., 1981. The nature and distirbution of upper Cenozoic ignimbrite centres in the Central Andes. J. Volcanol. Geotherm. Res. v11, p293-315.
Francis, P.W., & de Silva, S.L., 1989. Application of the Landsat Thematic Mapper to the identification of potentially active volcanoes in the Central Andes. Rem. Sens. Environ. v28, p245-255.
Francis, P.W., Thorpe, R.S., Brown, G.C., & Glassock, J., 1980. Pyroclastic sulphur from Poas volcano, Costa Rica. Nature v283, p754-756.
Markham, B.L., & Barker, J.L., 1986 Landsat MSS and TM post-calibration dynamic ranges, exoatmospheric reflectances and at-satellite temperatures. EOSAT Tech. Notes 1, 3-8. Earth Obs. Satell. Co. Lanham, Maryland.