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Boletín de la Sociedad Geológica Mexicana
http://dx.doi.org/10.18268/BSGM2005v57n3a6 |
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Geología e historia eruptiva de algunos de los grandes volcanes activos de México
José Luis Macías
Departamento de Vulcanología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Del. Coyoacán, 04510,
México D. F.
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Abstract
Most of the largest volcanoes in Mexico are located at the frontal part of the Transmexican Volcanic Belt and in other isolated areas. In this paper were considered some of these volcanoes as follows: Colima, Nevado de Toluca, Popocatépetl, Pico de Orizaba (Citlaltépetl) and Tacaná. El Chichón volcano was also considered within this group because of its 1982 catastrophic eruption. The volcanic edifice of these volcanoes or part of it, has been constructed during late Pleistocene or even during the Holocene: Colima during the last 2 500 years, Pico de Orizaba 16 500 yr, Popocatépetl 23 000 yr, Tacaná ~26 000 yr, and Nevado de Toluca >50 000 yr. The modern cones of Colima, Popocatépetl, Pico de Orizaba and Tacaná are built inside or besides the remains of older caldera structures left by the collapse of ancestral cones. Colima, Popocatépetl, and Pico de Orizaba represent the youngest volcano of nearly N-S volcanic chains. Despite the repetitive history of cone collapse of these volcanoes, only Pico de Orizaba has been subjected to some studies of hydrothermal alteration and slope stability crucial to understand future potential events of this nature. The magmas that have fed these volcanoes have a general chemical composition that varies from andesitic (Colima and Tacaná), andesitic-dacitic (Nevado de Toluca, Popocatépetl, and Pico de Orizaba) to trachyandesitic (Chichón). These magmas are the result of several magmatic processes that include partial melting of the mantle, crustal assimilation, magma mixing and fractional crystallization. So far, we know very little about the deep processes that occurred between the upper mantle source and the lower crust. However, new data have been acquired on shallower processes between the upper crust and the surface. There exist clear evidences, that most of these magmas have stagnated at shallow magma reservoirs prior to erupt; these depths vary from 3-4 km at Colima volcano, ~6 km at Nevado de Toluca, and 6-12 km at Chichón volcano.
Over the past 15 years, there has been a surge of studies dealing with the volcanic stratigraphy and eruptive history of these volcanoes. Up today no efforts have been achieved to integrate all the geological, geophysical, chemical, and petrological information to produce conceptual models of these volcanoes. Therefore, we still have to precise the size and location of the magma chambers, magma ascent paths and time intervals prior to an eruption, to construct hazard maps to finally establish permanent long-running monitoring systems. Today, only Colima and Popocatépetl have permanent monitoring networks, while Pico de Orizaba, Tacaná, and Chichón have a few seismic stations. Of these, Popocatépetl, Colima, and Pico de Orizaba have volcanic hazard maps that constitute the basic information needed by the Civil Defense authorities, to elaborate information programs to the population as well as evacuation plans in case of a future eruption.
Keywords: Geology, eruptive chronology, active volcanoes, Mexico.
