Stratigraphy of the crater and morphology of Cerro Machín volcano, Colombia

Abstract

The Cerro Machín Volcano (CMV) is located on the eastern flank of the Central Cordillera of Colombia, 17 km west of the city of Ibagué (Tolima). The CMV, a dacitic Holocene volcano, has evidence of multiple considerable eruptions (VEI 5). The inner walls of the crater display a sequence of dilute pyroclastic density currents (PDC) deposits, which contain characteristics of basal surge deposits. The presence of accidental lithics indicates that the basement of the volcano was involved in the magmatic fragmentation process. It is, thus possible to suggest that water-magma interaction played an important role in the dynamics of the last eruptive event, which formed the deposits that molded the crater. On the other hand, a morphological analysis revealed that the crater is 2.4 km in diameter, has an opening which faces the southwestern sector, and carries a dome of 490 m in height. Thus, it is interpreted that the growing dome destroyed the crater during its emplacement. Although the CMV is undoubtedly a polygenetic volcano (six eruptions in the last 5000 years), the sedimentological and morphological characteristics of the crater deposits suggest a monogenetic tuff cone structure. In conclusion, the CMV should be defined as a "composite volcano with tuff cone morphology".