Abstract Determining the timescales of magma degassing is essential for understanding the mechanisms controlling the eruption style and the dynamics of magmatic systems. Towards this end, we measured 210 Pb– 226 Ra disequilibria in andesite lavas erupted from Volcán de Colima between 1998 and 2010. ( 210 Pb/ 226 Ra) 0 activity ratios range from 0.86 to 1.09, and are best explained in terms of 222 Rn degassing and accumulation. The range in 210 Pb deficits indicates that the timescales of 222 Rn degassing did not exceed 11 years. 210 Pb excesses are rare and small (<10%), which signifies that 222 Rn degassing is more effective than 210 Pb accumulation in this intermediate system despite the relatively low gas output at the surface. The absence of significant 210 Pb excesses strongly suggests that the volcanic activity results from episodic ascent of small magma batches through the vapour-saturated section of the magmatic system. Overall, the degassing models based on 210 Pb– 226 Ra disequilibrium suggest an open and complex subvolcanic magmatic system comprising several conduits in which multiple magma batches reside for up to 10 years. Shifts from effusive to explosive Vulcanian eruptive phases are not related to changes in degassing mode on timescales resolvable using 210 Pb– 226 Ra disequilibria.

During the past 15 yr, volcanological studies in Mexico have been mostly focused on the pyroclastic stratigraphy and petrologic evolution of the volcanoes, with very little attention paid to detailed mapping of volcanic areas. In this study, we present a geologic map of the Colima volcanic complex, which covers ~3780 km 2 . The Colima volcanic complex is made of El Cántaro, Nevado de Colima, Paleofuego, and Colima volcanoes, totaling 422 km 3 in volume. The activity of the Colima volcanic complex started at El Cántaro with the emission of lava flows and domes ca. 1.7 Ma. About 0.53 Ma, 15 km southward, the formation of Nevado began with the emission of lava flows. Nevado produced at least four collapses that generated debris avalanches, debris flows, and pyroclastic-flow deposits. During late Pleistocene (>>38,500 yr B.P.), the formation of Paleofuego began 5 km further south with the emission of lava flows. Paleofuego collapsed at least five times, producing debris avalanches and pyroclastic-flow deposits. The last collapse of Paleofuego, at 2505 yr B.P., produced a 5-km-wide caldera, inside of which grew Colima volcano. Colima is the most active volcano in Mexico, with 45 eruptions during the past 426 yr, representing a potential hazard for the surrounding population of ~0.9 million people. From the geological mapping, it is clear that volcanic activity and collapses of the Colima volcanic complex have been controlled by the active Tamazula fault, which generated the NE-SW Alceseca-Atenquique graben.

Most of the largest volcanoes in México are located at the frontal part of the Trans-Mexican Volcanic Belt and in other isolated areas. This chapter considers some of these volcanoes: Colima, Nevado de Toluca, Popocatépetl, Pico de Orizaba (Citlaltépetl), and Tacaná. El Chichón volcano is also considered within this group because of its catastrophic eruption in 1982. The volcanic edifice of these volcanoes, or part of it, was constructed during the late Pleistocene or even during the Holocene: Colima 2500 yr ago, Pico de Orizaba (16,000 yr), Popocatépetl (23,000 yr), Tacaná (∼26,000 yr), and Nevado de Toluca (>45,000). The modern cones of Colima, Popocatépetl, Pico de Orizaba, and Tacaná are built inside or beside the remains of older caldera structures left by the collapse of ancestral cones. Colima, Popocatépetl, and Pico de Orizaba represent the youngest volcanoes of nearly N-S volcanic chains. Despite the repetitive history of cone collapse of these volcanoes, only Pico de Orizaba has been subjected to hydrothermal alteration and slope stability studies crucial to understand future potential events of this nature. The magmas that feed 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 is clear evidence that most of these magmas stagnated at shallow magma reservoirs prior to eruption; these depths vary from 3 to 4 km at Colima volcano, 4.5–6 km at Nevado de Toluca, and ∼6–8 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 to the present, no efforts have achieved integration of the geological, geophysical, chemical, and petro logical information to produce conceptual models of these volcanoes. Therefore, we still have to assume the size and location of the magma chambers, magma ascent paths, and time intervals prior to an eruption. 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 provide the basic information needed by the civil defense authorities to establish information programs for the population as well as evacuation plans in case of a future eruption.

Colima volcano is situated at the western edge of the Mexican volcanic belt within the Colima rift zone. This contribution presents new geochemical and Sr-Nd-Pb-O isotope data for Colima volcano rocks and plutonic xenoliths found in prehistorical lava flows. Colima volcano magmas display strong subduction signatures (positive peaks of Ba, K, Pb, and Sr, and negative anomalies of Nb and Ti) and were generated in a depleted mantle source and emplaced at crustal levels (garnet-free zone), where they experienced fractional crystallization of plagioclase and pyroxene. Gabbroic and granitoid xenoliths found in prehistorical lava flows show evidence for partial melting and are considered to be representative of the basement beneath Colima volcano. At upper-crustal levels, Colima volcano magmas were contaminated by granitoids, like those of the nearby Cretaceous Manzanillo and Jilotlán Batholiths. Sr-Nd isotope ratios of these intrusives are nearly identical to those of Colima volcano lavas. For that reason assimilation of the granitic crust is not detectable in diagrams of these isotopic systems but can be clearly seen in a ϵ Nd versus δ 18 O plot. In comparison to other large Mexican volcanic belt stratovolcanoes, Colima volcano lavas display the least evolved geochemical and isotopic signatures of this arc.

Volcanic explosions expel fragments following ballistic trajectories. The volcanic ballistic projectiles represent a hazard due to their high velocities and temperatures. They may affect people, ecology, infrastructure, and aircraft. In order to avoid volcanic ballistic projectile-related hazards, a map can be constructed. A volcanic ballistic projectiles hazard map depicts the likely distribution and maximum range of ballistic projectiles under given explosive scenarios. Different level hazard zones shown on the map allow local inhabitants and concerned authorities to make development, protection, and mitigation plans, and to define restricted areas. In order to determine the potential areas where the ballistics may fall, it is necessary to estimate their maximum range under different explosive scenarios. Explosive magnitude scenarios are defined by their characteristic kinetic energy. Therefore, the ballistic projectiles reach maximum distance from the source according to the maximum energy for each scenario. The trajectories described for the ballistic projectiles are determined by gravity and drag forces. Drag force depends, among other factors, on the drag coefficient (a function of the geometry of the ballistics). The maximum range of the projectiles depends also on the initial kinetic energy, the “launching” angle, the ballistic diameter, and the wind velocity. Another relevant aspect is that drag force is proportional to the air density (which decreases with altitude), and so projectiles with a given velocity (or kinetic energy) reach larger distances and heights at volcanoes with higher altitudes. This fact is important in the case of Volcán de Fuego de Colima (México) where the crater altitude is 3860 m above sea level. This work presents a useful hazards map for Volcán de Fuego de Colima based on ballistic data from this and other volcanoes.

A new numerical code for simulating flows of granular material, TITAN2D, is used to model the Merapi-type block and ash flows resulting from the 1991 eruption of Colima Volcano, México. The 1991 block and ash flows reached distances of up to 4 km from the vent with a total estimated volume of 8 × 10 5 m 3 . The block and ash flows were modeled using a digital elevation model (DEM) of the region and compared to field data using a quantitative center-line comparison method. Input parameter values, which dictate flow dynamics, were varied to demonstrate the effect these parameters have on the program output. Analysis showed that the TITAN2D model performs best in replicating the center lines of the 1991 Colima block and ash flows when using an initial volume value representative of a single flow event rather than a total deposit volume.