This report describes the petrology and geochemistry of the active volcano of Nevados de Chillán, which is situated at 36° 50'S in the Southern Volcanic Zone of the Chilean Andes.
The study has been carded out at the University of Bristol as part of a broader assessment of the volcanic hazards of Nevados de Chillán, which is being undertaken in collaboration with the Servicio Nacional de Geología y Minería of Chile, the British Geological Survey and the University of Lancaster. The Nevados de Chillán hazard assessment in turn forms part of a wider ranging project entitled Volcanic Hazard Mapping for Development Planning (R5563), which is funded by the Emergency Aid Department of the Overseas Development Administration (ODA). It is led and co-ordinated by the British Geological Survey under the ODA/BGS Technology Development and Research Programme as part of the British Government's provision of aid through technical assistance to the developing countries.
The objective of the Nevados de Chillán project is to undertake a volcanic hazard assessment of the volcano using both conventional and experimental mapping techniques, with a view to developing and evaluating methods for the rapid mapping of volcanic hazards and production of hazard zone maps for use by planners and related agencies in developing countries.
A first phase of field survey work was undertaken on Nevados de Chillán in February and March 1994, and a second and final phase is being carried out at present. Following the first phase of fieldwork a number of questions arose concerning the stratigraphy and evolution of the volcano, and in particular the relationships between various lava groups that have been erupted from different volcanic centres on the Nevados de Chillán complex.
The evaluation of volcanic hazards requires a knowledge and understanding of the structure and geological evolution of a volcanic centre. The petrological and geochemical study described in this report was undertaken to help elucidate the problems related to lava classification and stratigraphy at Nevados de Chillán, and also to gain an insight into the nature of the magmatic processes operating within and beneath the volcano. The investigation was carried out in close collaboration with other members of the project team who are concerned primarily with the geological mapping and hazard assessment. Through an iterative process drawing upon the petrological and geochemical data, as well as photogeological interpretations and field observations, it has been possible to refine the stratigraphy and geological map of the volcano. This has resulted in a better understanding of the evolution and eruptive history of the volcano as a whole, which will ultimately be reflected in a more realistic assessment of the nature, distribution and impact of potential hazards on the surrounding region.
Report available in full colour (8609 kb) and black and white (5773 kb).