ABSTRACT We generated low-temperature thermochronological data on crystalline rocks from the Chiapas Massif in southern Mexico to constrain the complex relationship among tectonics, exhumation, and sedimentation in the region. Our data show that the first recorded cooling event occurred at ca. 40–25 Ma due to denudation of the sedimentary cover of the Chiapas Massif at slow rates of ~0.1 km/m.y. This was followed by a period of tectonic quiescence from ca. 25 to 14 Ma. Between ca. 14 and 7 Ma, cooling implying exhumation of the massif at rates of up to ~0.7 km/m.y. was renewed, and this was associated with, and possibly responsible for, the Miocene “Chiapanecan” deformational event observed in the Chiapas fold-and-thrust belt to the northeast of the massif. This younger uplift was also accompanied by the onset of arc-related magmatism beneath the massif, between ca. 13 and 9 Ma, along the Tonalá shear zone at the Pacific coast. Since ca. 7 Ma, additional but slower cooling and exhumation are indicated along the length of the Chiapas Massif, and arc magmatism has jumped north by ~125 km from the Tonalá shear zone into the Chiapas fold-and-thrust belt. Concurrently, subsidence and sedimentation have persisted along the offshore Tehuantepec Shelf to the south, suggesting that the Tonalá shear zone has been recently active (despite no magnitude 4 or larger earthquakes), with up-to-the-north vertical displacement. We interpret the exhumation at ca. 40–25 Ma to pertain to displacement of the Chortis block along the paleo–Motagua fault zone, either as a northward propagation of a basement thrust beneath the massif within a regional transpressional setting, or as a deep, ductile crustal thickening and attendant isostatic uplift of the southern flank of the massif during the transpressional passage of the Chortis block. The ensuing quiescence (25–14 Ma) coincided, we believe, with the passage of the “western tail” of Chortis, which is internally deformed and perhaps transferred compressive stress less effectively than had the central, continental core of the Chortis block earlier. Renewed uplift and exhumation of the region began by ca. 14–10 Ma. An onset at ca. 10 Ma is probably the best estimate for the beginning of exhumation of the northwestern and central portions of the Chiapas Massif, whereas the present-day southeastern tip of the massif (potentially an allochthonous sliver belonging to the Chortis block) started to exhume earlier, at ca. 14 Ma. By ca. 13 Ma, arc magmatism had moved into the western Tehuantepec area, marking the onset of subduction of the Cocos plate beneath the Chiapas Massif. Hence, we interpret the main period of uplift of the Chiapas Massif and primary shortening of the Chiapas fold-and-thrust belt (ca. 14–7 Ma) as being driven by the establishment of Cocos subduction beneath the area.

ABSTRACT A comprehensive correlation chart of Pennsylvanian–Eocene stratigraphic units in Mexico, adjoining parts of Arizona, New Mexico, south Texas, and Utah, as well as Guatemala, Belize, Honduras, and Colombia, summarizes existing published data regarding ages of sedimentary strata and some igneous rocks. These data incorporate new age interpretations derived from U-Pb detrital zircon maximum depositional ages and igneous dates that were not available as recently as 2000, and the chart complements previous compilations. Although the tectonic and sedimentary history of Mexico and Central America remains debated, we summarize the tectonosedimentary history in 10 genetic phases, developed primarily on the basis of stratigraphic evidence presented here from Mexico and summarized from published literature. These phases include: (1) Gondwanan continental-margin arc and closure of Rheic Ocean, ca. 344–280 Ma; (2) Permian–Triassic arc magmatism, ca. 273–245 Ma; (3) prerift thermal doming of Pangea and development of Pacific margin submarine fans, ca. 245–202 Ma; (4) Gulf of Mexico rifting and extensional Pacific margin continental arc, ca. 200–167 Ma; (5) salt deposition in the Gulf of Mexico basin, ca. 169–166? Ma; (6) widespread onshore extension and rifting, ca. 160–145 Ma; (7) arc and back-arc extension, and carbonate platform and basin development (ca. 145–116 Ma); (8) carbonate platform and basin development and oceanic-arc collision in Mexico, ca. 116–100 Ma; (9) early development of the Mexican orogen in Mexico and Sevier orogen in the western United States, ca. 100–78 Ma; and (10) late development of the Mexican orogen in Mexico and Laramide orogeny in the southwestern United States, ca. 77–48 Ma.

Abstract High permeability and rapid recharge in karst aquifers make them susceptible to contamination. We combined a groundwater vulnerability map with an environmental disturbance index to give an adaptable spatial tool for developing management strategies for a karst environment in the Reserva de la Biosfera Selva el Ocote (el Ocote), Chiapas, Mexico. Seventy-two per cent of the study area is classified as an area of least concern for management, with 60% falling within el Ocote. Consequently, although there are concerns regarding the vulnerability of the karst ecosystem, the lack of development and the natural protection of the ecosystem, the immediate need for remedial action by the area’s managers is currently minimal. About 27% of the study area is classified by the composite model as of moderate concern, with 34% within el Ocote. This reflects a balance between areas of moderate and high vulnerability, but little disturbance. Based on the management zones created by this study, much of the sub-catchment is zoned as of least or moderate concern, where disturbance has not occurred. As such, the opportunity exists to prevent major human impacts on vulnerable areas and the entire ecosystem, but only if local stakeholders are incorporated into this process of limiting development.

Efforts to improve water quality and quantity, and sanitation in the world are impeded by a variety of technical and socioeconomic issues often unfamiliar to well-motivated individuals. Sustainable technological improvement can be thwarted by the lack of consideration of regional norms, customs, mores, and traditions, and by the absence of feasibility assessment and coordination with the community both before and during instatement of local improvements. Specifically, the absence of coordination means not fully allowing users to define their needs, resources, issues, and maintainable solutions, and not understanding local and regional power dynamics and the ability of the community to provide long-term project stewardship. Other mistakes can include: a lack of long-term planning; inadequate scientific and engineering design and construction; lack of anticipation of contingencies and complicating issues and lack of adaptive management to deal with these unforeseen events; use of inappropriate technology; absence of educational efforts (both for the community to understand and provide stewardship for the project, and for the education of those installing the facilities in the community); lack of follow-up; and lack of technical expertise and leadership. There is no single approach to water and sanitation development that fits all situations. However, avoiding common pitfalls can bring these important resources to villages worldwide, and in the process empower communities, reduce sickness and mortality, and improve the human condition.

Collapse of masonry buildings still accounts for most earthquake casualties in developing countries, even though effective earthquake-resistant building techniques are available. The amateur builders and local contractors who are responsible for most housing and small-scale commercial construction are typically unaware of these techniques, or they believe that prohibitively expensive engineering design and materials are required. However, the principal technique—confined masonry—is highly effective for nonengineered buildings of less than three stories, and it involves only modest changes in customary building practices. I developed a 2 hour workshop to teach local builders in Guatemala earthquake-resistant construction techniques. Simple graphics with minimal captions and photographs of local buildings were used to show basic design principles, and to illustrate best versus poor practices. Printed manuals (in Spanish and illustrated for a low-literacy audience) were provided, for later reference and the possibility of wider dissemination. The most challenging aspect of this project was developing a working relationship with a local organization willing and able to assist with scheduling, publicity, and generally connecting me with appropriate audiences. My experience suggests that effective teaching is the most critical tool for providing meaningful assistance with a range of geologic and environmental challenges. Expert knowledge, fluency in local languages, and years of local experience are all useful but can be provided or developed through relationships with local partners. Targeted education addressing specific community needs can be highly effective for increasing resilience to natural hazards, and it represents a more-efficient and lower-cost alternative to many other forms of development aid.

Fuego Volcano (14°29′N, 90°53′W, 3800 m) is the southernmost vent of the north-south–trending Fuego-Acatenango volcanic complex. A basaltic-andesite stratovolcano, Fuego has had more than 60 subplinian eruptions since A.D. 1524, making it one of the most active volcanoes in the world. Since 1999, Fuego has exhibited continuous low-level activity, which alternates between periods of lava effusion with Strombolian explosions and periods of discrete explosions with no lava effusion. We analyzed explosions recorded on a broadband seismometer and infrasonic microphones in June and July 2008. The explosions were identified through a combination of visual field observations and the examination of infrasound records. Acoustic waveform cross-correlation indicated a highly repetitive source appropriate for investigating temporal variations in the wave field. The primary focus of this study is a time period from 8 to 27 June 2008, which included the emergence of a new lava flow. Using seismic coda wave interferometry analysis of 159 well-recorded explosions, we detected short-term relative changes in the velocity structure ranging from −0.23% to 0.61%. This rapid variation may indicate minor fluctuations in volatile content. Variations in seismic and acoustic wave arrival time differences, which might result from changes in source depth, are attributed to wind speed variations.