Northern Central Andes, Peru
Structure and Evolution
Nevado Chachani is a collection of spatially related volcanic vents covering an area of ~360 km2, located about 20 km north of the city of Arequipa (pop. ~ 900,000). It consists of three main structural elements: (1) the pre-Holocene Cerro Nocarane (CN) and dome, Cerro Los Peñones (CP), in the north, (2) the younger Nevado Chachani (C), an arcuate volcanic ridge in the central part of the complex, and (3) a large mass of lava , the Pampa de Palacio (Las Cortaderas in Bullard, 1962), in the south (PP). Post-glacial activity appears to be confined to the latter two elements .
Thin lava flows (L) from the central and western portions of Nevado Chachani overlie moraines and a well defined summit crater (SC) is present on the westernmost cone of Chachani. A small ash cone, Cerro La Horqueta (H), may represent the last activity from Cachani. Activity then migrated southwards to the Pampa de Palacio, which represents the youngest activity from the Nevado Chachani. Here, several eruptions have given rise to numerous short, thick, stubby lava flows forming a domical mass some 8 km in diameter and about 1 km thick. Notwithstanding the fact that these flows occur at lower elevations and therefore may have been better preserved than those at the higher, wetter elevations on Chachani, they are pristine and display excellent levée and ridge morphologies. Extrusion of a passive dome-like mass on which two vents can be discerned appears to have been the last phase of activity. The largest activity at this volcano may have occurred in the neogene and quarternary, when three of four of the large Arequipa ignimbrites are thought to have sources below the present-day Chachani complex. These include the La Joya Ignimbrite sheet (4.87 Ma, 20 km
Although no current or historic activity has been reported from this complex, thermal springs at Yura and Socosani, on the western and southwestern flanks of Chachani respectively, may be evidence for an active hydrothermal system beneath Chachani.
Chachani presents a significant hazard potential, particularly because of its height and proximity to Arequipa. Suburbs of Arequipa west of the Rio Chili (RC) are particularly vulnerable to pyroclastic or mud flows. These are located less than 25 unobstructed kilometers horizontally and 3,000 m vertically from the summit of Chachani.
Bullard, F.M. 1962. Volcanoes of southern Peru. Bull. Volcanol. XXIV: 445-453.de Silva S.L., & Francis, P.W., 1990. Potentially active volcanoes of southern Peru - observations using Landsat Thematic Mapper and Space Shuttle imagery. Bull. Volcanol. 52, 286-301.
Lepti, P.P., Thouret, J.C., Wörner, G., Fornari, M., 2006. Neogene and Quaternary ignimbrites in the area of Arequipa, Southern Peru: