Structure and Evolution
Llullaillaco, the second highest volcano in the world, is situated in a remote part of the region on the Chile-Argentina border (Figure 34.1). Gardeweg et al. (1984) recognize two major evolutionary stages in the history of the volcano. Llullaillaco I, the ancestral volcano, which has a history dating back to the Pleistocene (1.5 + 0.4 Ma), is now represented by two deeply eroded cones and associated lava flows; some of which are up to 20 km in length and are distributed mainly to the west. Llullaillaco II is the present post-glacial edifice (L) which may have been active in historic times (Bruggen, 1950; Casertano, 1963) and is a small, well preserved cone built upon Llullaillaco I (Figure 34.2). Several lava domes and flows (youngest dated at 0.048 +/- 0.012 Ma) are associated with this phase; the two most conspicuous being distributed north and south of the volcano respectively (LF; Figure 34.3). Hot avalanche deposits, extending up to 3 km, are associated with one of the southern lava flows (Figure 34.3).
Francis & Wells (1988) described a major débris avalanche deposit from the eastern flank of Llullaillaco (DF). Richards and Villeneuve (2001) determined the cause of the collapse to be oversteepening of the flanks, and dated the event at or after 0.15 Ma. An interesting aspect of the avalanche is that it over-ran the older Cerro Rosado (CR) 17 km east of Lulullailaco, leaving a conspicuous 'high tide mark', and split into two lobes that travelled eastwards for a further 5 km, terminating on the shores of the Salar de Lullaillaco (Figure 34.4).
There are reports of eruptions in 1854, 1868 and 1877 (Bruggen, 1950). It is possible that these yielded the extremely youthful lava flows on Llullaillaco, which are conspicuous because of their very low albedos and pristine morphologies (Figure 34.2). The 500-year-old bodies of three Incan children have been found at the summit, indicating.
No current activity is known.
Gardeweg et al. (1984) made a preliminary petrological investigation of the lavas on the western flanks of the volcano and reported that Llullaillaco is dominated by hornblende-plagioclase-biotite dacites. They report that there is petrographic evidence for magma mixing during the evolution of the magmas. The dacites are typically K-rich, with Rb/Sr ratios of 0.06-0.14, which are similar to Socompa but different from those reported from other volcanoes in the Central Andes. The later Llullaillaco II lavas are more differentiated and enriched in K2O, NaO, Sr, and Ba than those from Llullaillaco I. Richards and Villeneuve (2001) have done further geochemical work.
Bruggen, J., 1950., Fundamentos de la Geologia de Chile. Inst. Geogr. Militar. (Chile) 374p. Santiago
Casertano,L., 1963. Catalogue of the active volcanoes of the world; Part XV, Chilean continent I.A.V.C.E.I. Naples, Italy, 55pp.
Francis, P.W., & Wells G.L., 1988 Landsat Thematic Mapper observations of débris avalanche deposits in the Central Andes. Bull Volcanol. 50:258- 278.
Gardeweg, M., Cornejo, P., & Davidson, J., 1984. Geologia del Volcan Llullaillaco, altiplano de Antofagasta, Chile (Andes Centrales). Rev. Geol. de Chile. 23:21-37.
Richards, J.P., and Villeneuve, M., 2001. The Llullaillaco volcano, northwest Argentina: construction by Pleistocene volcanism and destruction by sector collapse. Journal of Volcanology and Geothermal Research, 105(1-2):77-105.