Stratigraphy and chronology of the Galeras volcanic complex, Colombia

An understanding of the evolution of the Galeras volcanic complex (GVC) is critical for assessing and refining hazards and eruption forecasting for the current reactivation of Galeras volcano. Detailed field geology and dating by14C and40Ar-39Ar methods help establish a comprehensive stratigraphie framework, defining six different stages in the evolution of the Galeras volcanic complex. The two oldest stages, Cariaco and Pamba, represent the westernmost activity of the complex. The next stage, Coba Negra, had a caldera-forming eruption that occurred about 560 ka ago. The Coba Negra edifice, which was partially destroyed by this eruption, had a total volume of about 70 km3. The volume of pyroclastic flow deposits related to caldera formation is about 16 km3. The caldera, which has been partially destroyed, was about 5 km in diameter. The next constructional stage, Jenoy, had an edifice volume of about 64 km3. The caldera-forming event that ended this stage took place sometime between 150 and 40 ka ago. Deposits from these eruptions are found in the northeastern and southeastern slopes of the complex and have a volume of approximately 2 km3. The center of the Jenoy caldera was located east-southeast from the center of the previous Coba Negra caldera, probably along the rim of the former caldera. The diameter of the Jenoy caldera was about 4 km. A summit collapse, probably not eruption-related, occurred between 12 and 5 ka ago, during the Urcunina stage. Hydrothermally altered rocks which are found in the scar of the collapse suggest that it may have been related to instabilities created by the circulation of hydrothermal fluids in addition to a very steep slope in the western part of the edifice. The approximately 4 km3 missing from the top of the volcano agrees very well with approximately 3 km3 of avalanche deposits found near the town of Consaca 12 km west of the present-day summit. The system at the GVC has produced large, hazardous eruptions, although in the most recent years (less than 5 ka) the eruptions have been of small scale.