Abstract New data on the pyroclastic density current (PDC) deposit temperature ( T dep ) are provided for two prominent eruptions of Mexican volcanoes of the twentieth century: the 1982 eruption of El Chichón and the 1913 eruption of Colima. In spite of similar lithofacies, magma composition and pre-eruptive conditions, the T dep of the PDCs from the 1982 (El Chichón) and 1913 (Colima) eruptions differ significantly, with intervals of T dep of 360–420 °C and 250–330 °C, respectively. These new data emphasize that a full understanding of the physical mechanisms responsible for equilibrium temperature attainment within a pyroclastic deposit has not yet been realized. The T dep measured for El Chichón PDC deposits confirm the preliminary data published elsewhere, while Colima magnetic temperatures provide different values to those published previously. Supplementary material: T dep measurements for the different sites at El Chichon volcano and Colima volcano are available at: http://www.geolsoc.org.uk/SUP18695 .

Abstract Los Azufres Volcanic Field hosts the second most important geothermal field of Mexico, with a production of 188 MW of electricity. Based on fieldwork and new geochronological data ( 14 C and 40 Ar/ 39 Ar) we define that activity at Los Azufres Volcanic Field started some 1.5 Ma with the emission of basaltic to rhyolitic lavas, and pyroclastic material. The late Pleistocene explosive activity in the southwest sector (Guangoche volcano area) of Los Azufres occurred in a narrow period of time between >31 and <26 ka. The pyroclastic stratigraphy of the S, SW, and W sectors is represented by diverse deposits of dacitic and rhyolitic composition, including a debris avalanche deposit related to a sector collapse of San Andrés volcano, several pyroclastic sequences associated with plateau forming lavas, and Guangoche volcano. Guangoche volcano was the focus of late Pleistocene eruptive activity with two Plin-ian and one subplinian events that deposited pumice-rich falls and pyroclastic flows and surges. These deposits are informally named the White Pumice (29 ka), which originated from a 23-km-high eruptive column and the ejection of 1.7 km 3 of tephra that covered an area of at least 223 km 2 with a mass discharge rate of 9 × 10 7 kg/s; the Ochre Pumice fall (<26 ka), deposited from a 16-km-high eruptive column involving 1.3 km 3 of tephra at a mass discharge rate of 1.9 × 10 7 kg/s; and the Multilayered fallout (<<26 ka) that resulted from an 11-km-high eruptive column with 1 km 3 of tephra at a mass discharge rate of 4.6 × 10 6 kg/s. The complete late Pleistocene stratigraphy suggests that explosive events at Los Azufres Volcanic Field have been intense. They are the subject of ongoing investigations to better understand this kind of large magnitude eruptions.

The Tacaná Volcanic Complex represents the northernmost active volcano of the Central American Volcanic Arc. The genesis of this volcanic chain is related to the subduction of the Cocos plate beneath the Caribbean plate. The Tacaná Volcanic Complex is influenced by an important tectonic structure as it lies south of the active left-lateral strike-slip Motozintla fault related to the Motagua-Polochic fault zone. The geological evolution of the Tacaná Volcanic Complex and surrounding areas is grouped into six major sequences dating from the Mesozoic to Recent. The oldest basement rocks are Mesozoic schists and gneisses of low-grade metamorphism. These rocks are intruded by Tertiary granites, granodiorites, and tonalites ranging in age from 12 to 39 Ma, apparently separated by a gap of 9 m.y. The first intrusive phase occurred during late Eocene to early Oligocene, and the second during early to middle Miocene. These rocks are overlain by deposits from the Calderas San Rafael (ca. 2 Ma), Chanjale (ca. 1 Ma), and Sibinal (unknown age), grouped under the name Chanjale–San Rafael Sequence, of late Pliocene–Pleistocene age. The activity of these calderas produced thick block-and-ash flows, ignimbrites, lavas, and debris flows. The Tacaná Volcanic Complex began its formation during the late Pleistocene, nested in the preexisting San Rafael Caldera. The Tacaná Volcanic Complex formed through the emplacement of four volcanic centers. The first, Chichuj volcano, was formed by andesitic lava flows and pyroclastic deposits, after which it was destroyed by the collapse of the edifice. The second, Tacaná volcano, formed through the emission of basaltic-andesite lava flows, as well as andesitic and dacitic domes that produced extensive block-and-ash flows ∼38,000, 28,000, and 16,000 yr B.P. The Plan de las Ardillas structure (the third volcanic center) consists of an andesitic dome with two lava flows emplaced on the high slope of the Tacaná ∼30,000 yr B.P. Finally, the San Antonio volcanic center was built through the emission of lava flows, andesitic and dacitic domes, and it was destroyed by a Peléan eruption at 1950 yr B.P. that produced a block-and-ash flow deposit. The Tacaná Volcanic Complex was emplaced along a NE-SW trend beginning with Chichuj, followed by Tacaná, Las Ardillas, and San Antonio. This direction is roughly the same as the NE-SW Tacaná graben (as proposed in this work), together with other faults and fractures exposed in the region. The rocks of the Chanjale-San Rafael Sequence and the Tacaná Volcanic Complex have a calc-alkaline signature with medium K contents, negative anomalies of Nb, Ti, and P, and enrichment in light rare earth elements, typical of subduction zones.

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.