Tephrochronological studies carried out over the past decade in the area surrounding Mexico City have yielded a wealth of new radiocarbon ages from eruptions at Popocatépetl, Nevado de Toluca, and Jocotitlán stratovolcanoes and monogenetic scoria cones in the Sierra Chichinautzin Volcanic Field. These dates allow us to constrain the frequency and types of eruptions that have affected this area during the course of the past 25,000 yr. They have important implications for archaeology as well as future hazard evaluations. Late Pleistocene and Holocene volcanic activities at the stratovolcanoes are characterized by recurrent cataclysmic Plinian eruptions of considerable magnitude. They have affected vast areas, including zones that today are occupied by large population centers at Puebla, Toluca, and Mexico City. During Holocene time, Nevado de Toluca and Jocotitlán have each experienced only one Plinian eruption, ca. 10,500 yr B.P. and 9700 yr B.P. respectively. During the same period of time, Popocatépetl had at least four such eruptions, ca. 8000, 5000, 2100, and 1100 yr B.P. Therefore, the recurrence interval for Plinian eruptions is less than 2000 yr in this region. The last two Plinian eruptions at Popocatépetl are of particular interest because they destroyed several human settlements in the Basin of Puebla. Evidence for these disasters stems from pottery shards and other artifacts covered by Plinian pumice falls, ash-flow deposits, and lahars on the plains to the east and northeast of the volcanic edifice. Several monogenetic scoria cones located within the Sierra Chichinautzin Volcanic Field at the southern margin of Mexico City were also dated by the radiocarbon method in recent years. Most previous research in this area was concentrated on Xitle scoria cone, whose lavas destroyed and buried the pre-Hispanic town of Cuicuilco ca. 1665 ± 35 yr B.P. The new dates indicate that the recurrence interval for monogenetic eruptions in the close vicinity of Mexico City is also <2000 yr. The longest lava flow associated with a scoria cone was erupted by Guespalapa and reached 24 km from its source; total areas covered by lava flows from each monogenetic eruption typically range between 30 and 80 km 2 , and total erupted volumes range between 0.5 and 2 km 3 /cone. An average eruption rate for the entire Chichinautzin was estimated at ∼0.5 km 3 /1000 yr. These findings are of great importance for archaeological as well as volcanic hazard studies in this heavily populated region.

Abstract Tephrochronological studies carried out over the past decade in the area surrounding Mexico City have yielded a wealth of new radiocarbon ages from eruptions at Popocatépetl, Nevado de Toluca, and Jocotitlán stratovolcanoes and monogenetic scoria cones in the Sierra Chichinautzin Volcanic Field. These dates allow us to constrain the frequency and types of eruptions that have affected this area during the course of the past 25,000 yr. They have important implications for archaeology as well as future hazard evaluations. Late Pleistocene and Holocene volcanic activities at the stratovolcanoes are characterized by recurrent cataclysmic Plinian eruptions of considerable magnitude. They have affected vast areas, including zones that today are occupied by large population centers at Puebla, Toluca, and Mexico City. During Holocene time, Nevado de Toluca and Jocotitlán have each experienced only one Plinian eruption, ca. 10,500 yr B.P. and 9700 yr B.P. respectively. During the same period of time, Popocatépetl had at least four such eruptions, ca. 8000, 5000, 2100, and 1100 yr B.P. Therefore, the recurrence interval for Plinian eruptions is less than 2000 yr in this region. The last two Plinian eruptions at Popocatépetl are of particular interest because they destroyed several human settlements in the Basin of Puebla. Evidence for these disasters stems from pottery shards and other artifacts covered by Plinian pumice falls, ash-flow deposits, and lahars on the plains to the east and northeast of the volcanic edifice. Several monogenetic scoria cones located within the Sierra Chichinautzin Volcanic Field at the southern margin of Mexico City were also dated by the radiocarbon method in recent years. Most previous research in this area was concentrated on Xitle scoria cone, whose lavas destroyed and buried the pre-Hispanic town of Cuicuilco ca. 1665 ± 35 yr B.P. The new dates indicate that the recurrence interval for monogenetic eruptions in the close vicinity of Mexico City is also <2000 yr. The longest lava flow associated with a scoria cone was erupted by Guespalapa and reached 24 km from its source; total areas covered by lava flows from each monogenetic eruption typically range between 30 and 80 km2, and total erupted volumes range between 0.5 and 2 km3/cone. An average eruption rate for the entire Chichinautzin was estimated at ~0.5 km3/1000 yr. These findings are of great importance for archaeological as well as volcanic hazard studies in this heavily populated region.

Abstract Magma-wall-rock interaction contributes gases to evolving magmatic systems, and removes volatiles into the country rock. These processes happen at depth, far away from direct observation. Micro-analysis of particles collected from volcanic plumes can provide information about these processes. For Popocatépetl volcano, scanning electron microscope (SEM) and field emission gun SEM (FESEM/EDS) analysis of contact-metamorphosed particles from fallout ash reveal the presence of wollastonite, hercynite and glass of non-volcanic, contact-metamorphic origin. Condensates from the passively degassing plume show a wide variety of chemical elements and are rich in phosphorus, indicating a possible non-magmatic source for this element.

Abstract The Sierra Nevada Volcanic Range includes, from south to north, the active Popocatépetl (5452 m), Iztaccíhuatl (5272 m) with several volcanic edifices, Telapón (4000 m), and Tlaloc (4150 m) volcanoes. It has been generally assumed that volcanic activity has migrated from Tlaloc (north) to Popocatépetl (south) over time. New evidence obtained from previous studies, field reconnaissance, and radiometric dating indicate that magmatism at the Sierra Nevada Volcanic Range likely started at 1.8–1.4 Ma with the construction of Paleo-Tlaloc volcano, which is today buried by younger deposits. The activity continued between 1.07 and 0.89 Ma with the emplacement of dacitic domes (Puico, Yahualica, Yeloxochitl, Tearco, and Torrecillas), lavas and associated pyroclastic flows as the San Francisco (1 Ma), and Chicoloapan (0.9 Ma). Afterwards, the main edifice of modern Tlaloc was built up through the emission of dacitic lava flows (0.94–0.84 Ma). Iztaccíhuatl began its activity ca. 1.1 Ma with the formation of several volcanic edifices up to 0.45 Ma, time during which a Mount St. Helens—type event destroyed the southeastern flank of Los Pies Recientes cone, producing a debris avalanche and pyroclastic deposits. Telapón volcano formed approximately between 0.38 Ma and 0.34 Ma ago with the emplacement of lava flows and a dome that become quiescent afterwards. Apparently, ca. 0.32 Ma, Popocatépetl began its eruptive activity that continues today. Strikingly, Tlaloc reawakened with the emission of rhyolitic magma at 0.129 Ma followed by the emplacement of the El Papayo dacite (118 ka) to the south and Téyotl summit lavas (80 ka). Activity continued at Tlaloc with the generation of five explosive eruptions at 44, 38, 33, 31, and 25 ka and the growth of the summit dome. Coevally, Popocatépetl, at the southern end of the range, had collapsed twice to the south and had intense volcanic activity up until today. Holocene activity has taken place at Iztaccíhuatl with the 9 ka Buenavista dacitic lava flow and repetitive Plinian eruptions of Popocaté-petl including some historic events and the 1994—present eruption. Popocatépetl's reawakening reminded authorities, scientists, media, and the public of its potential risk. In fact, on 22 January 2001, the rapid collapse of an eruptive column generated scoria-rich pyroclastic flows that partly melted the glacier producing lahars. From the above considerations it is obvious that magmatism of the Sierra Nevada Volcanic Range did not keep a continuous north to south migrating path, but it rather shifted back and forth chaotically throughout its evolution. It is worth mentioning that major gaps presented in the eruptive sequence are most likely due to poor radiometric coverage of the area that may improve in the future.