Northern Central Andes, Peru
Structure and Evolution
Misti, a symmetrical cone of considerable scenic beauty immediately NNE of the city of Arequipa, has two concentric summit craters (SC). The outer crater has a maximum diameter of ~930m within which a 550m diameter scoria-rimmed inner crater is nested (Hantke & Parodi, 1966). This inner crater is slightly eccentric and merges with the eastern wall. The edifice is dissected on its NW flanks but is otherwise intact.
On the lower flanks of the volcano the ash-mantled terminations of youthful lava flows (e.g. L) are discernible, but the upper flanks are covered in a dark airfall deposits which may have accompanied the formation of the scoria rim of the inner crater. Much of the flat lying plain to the northeast of the volcano is mantled by dark tephra, probably carried by the prevailing south-westerly winds. Funnelling of winds between Misti and the mountain to the east (Cerro Tacune) and transport of tephra has led to the development of an impressive parabolic dune field (PD) extending for up to 20 km downwind. A detailed map can be found here.
Misti has been active numerous times since historic records began. The last strong eruption of Misti is thought to have occurred between 1438 and 1471 (McLelland et al., 1989). Many other eruptions have been reported since the mid-15th century. The most recent activity reportedly took place from May to October, 1948, during which the scoria deposit may have formed (Hantke & Parodi, 1966). There are reports of high temperature (>250 °C) fumarolic activity (Hantke & Parodi, 1966. A small lava dome appears to have been present within the inner crater on photographs taken in 1959. Thouret et al. (2001) found that ash falls have occurred every 500 to 1500 yr on average, while pumice falls have occured every 2000 to 4000 yr.
Intermittent fumarolic activity is often observed from the summit region. A report in 1984 indicates the presence of a dome about 150m in diameter within the summit crater, while a report in 1985 mentions that the crater had a "flat-floor" (McLelland et al., 1989). On August 7 and 8, 1985 fumarolic activity sent steam noisily up from 6 vents within the summit inner crater (Dominique, 1985). No thermal anomaly was visible at infrared wavelengths on the TM image acquired in 1986.
Peru's second largest city, Arequipa (A; pop. ~900, 000), is ~18 km horizontally and 2.5 km vertically from the summit. Furthermore, the city has spread outwards along the Quebrada El Guarangal on the western flanks of the volcano. This quebrada would be a major channel for lahars or pyroclastic flows during future eruptions. Mudflows from the loosely consolidated upper slopes would also utilize this channel. While the absence of extensive permanent ice on the volcano reduces the mudflow risk, a considerable hazard to Arequipa remains. Arequipa is built directly on ash and lahar deposits from the sub-plinian eruption of El Misti ~2000 years ago.
Bullard, F.M. 1962. Volcanoes of southern Peru. Bull. Volcanol. XXIV: 443-453.
de Silva S.L., & Francis, P.W., 1990. Active and potentially active volcanoes of southern Peru - observations using Landsat Thematic Mapper and Space Shuttle imagery. Bull Volcanol. 52, 286-301.
Dominique, M.D., 1985. Miscellaneous Information: El Misti. Bull Volcanol. 50, 66.
Hantke, G., & Parodi, A., 1966. Catalogue of the active volcanoes of the world; Part XIX, Colombia, Ecuador & Peru, I.A.V.C.E.I. Naples, Italy, 73pp
Thouret, J-C., Finizola, A., Fornari, M., Legeley-Padovani, A., Suni, J., and Frechen, M., 2001. Geology of El Misti Volcano near the city of Arequipa, Peru. Geological Society of America Bulletin , 113(12), 1593-1610
McLelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, T.C., (eds.) 1989. Global Volcanism 1975-1985. National Museum of Natural History. Prentice-Hall Inc., New Jersey, pp655.