Amatitlan, An actively resurging cauldron 10 km south of Guatemala City

A 14×16 km diameter collapse caldera has been recognized 10 km south of Guatemala City, Guatemala. The caldera is north of the presently active volcano Pacaya and west of Agua, a large stratovolcano. The caldera was not previously recognized because its eastern and western margins coincide with faults that outline the Guatemala City graben and because the northern margin of the caldera is buried by pyroclastic rocks. The existence of the northern caldera margin is now established by gravity data and a variety of geological observations including circumferential faults, hot springs, well-log data, and lithological changes in sedimentary rocks. A sequence of nine silicic pyroclastic deposits, totaling a volume of more than 70 km 3 dense rock were erupted from the caldera. The ages of these eruptions are mainly between about 300,000 years B.P. to less than 23,000 years B.P. The rocks erupted at the caldera and its associated vents consist of domes and nonwelded pyroclastic flow, surge, and fall deposits, mainly of rhyolitic to dacitic composition. Successive pyroclastic eruptions have generally become smaller in volume and more silicic with time. Major and minor element chemistry distinguish Amatitlan pyroclastics from those of other nearby calderas. The caldera lies at the intersection of an offset of the volcanic chain (the Palin Shear) and the faults along the volcanic front (Jalpatagua fault zone). The caldera has a heavily faulted resurgent dome crosscut by an impressive longitudinal graben. The graben\u27s alignment with the Jalpatagua fault zone suggests a genetic relationship. The longitudinal graben and resurgent dome are morphologically youthful and are the sites of many young silicic vents. Available seismic data show a heavy concentration of epicenters over the northern part of the resurgent dome, near a young silicic intrusion. The caldera is active and will probably erupt again. Over 1 million people live within 20 km and would be threatened in the event of a moderate eruption. Suggestions for future research focus on hazard assessment and forecastin

Pharmacologic prophylaxis for atrial fibrillation following cardiac surgery: a systematic review

Atrial Fibrillation (AF) is the most common arrhythmia occurring after cardiac surgery. Its incidence varies depending on type of surgery. Postoperative AF may cause hemodynamic deterioration, predispose to stroke and increase mortality. Effective treatment for prophylaxis of postoperative AF is vital as reduces hospitalization and overall morbidity. Beta - blockers, have been proved to prevent effectively atrial fibrillation following cardiac surgery and should be routinely used if there are no contraindications. Sotalol may be more effective than standard b-blockers for the prevention of AF without causing an excess of side effects. Amiodarone is useful when beta-blocker therapy is not possible or as additional prophylaxis in high risk patients. Other agents such as magnesium, calcium channels blocker or non-antiarrhythmic drugs as glycose-insulin - potassium, non-steroidal anti-inflammatory drugs, corticosteroids, N-acetylcysteine and statins have been studied as alternative treatment for postoperative AF prophylaxis

Architecture of the hidden Penokean terrane suture and Midcontinent rift system overprint in eastern Minnesota and western Wisconsin from magnetotelluric profiling

© 2017 The Authors. We resolved the architecture of the early Proterozoic Penokean orogen suture and late middle Proterozoic (Keweenawan) Midcontinent rift system magmatic overprint in east-central Minnesota and western Wisconsin through recovery and analysis of a legacy magnetotelluric (MT) data set. We digitized printed plots of off-diagonal MT and controlled-source audio (CSA) MT responses, including error intervals, to provide 22 soundings along a profile of ~225 km length extending from north of Lake Mille Lacs, Minnesota, southeastward to Flambeau Ridge, Wisconsin. the MT data were inverted to a smoothed electrical resistivity structure using a two-dimensional finite-element, regularized Gauss-Newton algorithm emphasizing the transverse magnetic (TM) mode data subset. Our model reveals a major electrically conductive zone dipping moderately to the southeast for \u3e 50 km in the 5-35 km depth range, which marks the probable Penokean suture in easternmost Minnesota. We interpret the conductor to reflect a package of graphitized metasediments of the former Archean continental margin and near foreland zone, underthrust as the Penokean terrane collided with the Superior Province. the large-scale conductor is now hidden beneath mainly Yavapai-aged plutonic rocks of the East-Central Minnesota batholith. Below the axis of the later Midcontinent rift (St. Croix horst, subsequently), a compact resistive body ranging from 5 to 20 km deep overlies the large conductor. We interpret this resistor to be mafic volcanic and intrusive rocks of the Midcontinent rift event, which correlate spatially with a high Bouguer gravity anomaly similarly modeled. the rift here coincides with the lower-crustal reaches of the suture, but the specific influence of the suture on rift emplacement is unclear

A volcanologist\u27s review of atmospheric hazards of volcanic activity: Fuego and Mount St. Helens

The large amount of scientific data collected on the Mount St. Helens eruption has resulted in significant changes in thinking about the atmospheric hazards caused by explosive volcanic activity. The hazard posed by fine silicate ash with long residence time in the atmosphere is probably much less serious than previously thought. The Mount St. Helens eruption released much fine ash in the upper atmosphere. These silicates were removed very rapidly due to a process of particle aggregation (Sorem, 1982; Carey and Sigurdsson, 1982; Rose and Hoffman, 1982). There is some evidence to suggest that particle aggregation is particularly successful in removing glass shards with high surface areas/mass ratios. The primary atmospheric hazard of explosive eruptions is volcanic sulfur, which is converted to sulfuric acid and sulfate crystals. Although the Mount St. Helens dacite magma had a very low sulfur content before eruption, the eruptions did make a significant contribution to the stratospheric sulfate layer (Newell, 1982). Evidence based on measurements of S and Cl in erupted rocks, glass inclusions, gas samples, and atmospheric samples collected for both Mount St. Helens and Fuego volcanoes, suggests that both volcanoes released substantial contributions of S from intrusive (non-eruptive) magma. The amount of sulfur contributed to the atmosphere by an explosive eruption thus depends not only on the volume of magma erupted and its sulfur content, but also on the degree of near-surface non-eruptive magma. The data collected to assess atmospheric hazard and to evaluate the processes and mechanisms of explosive volcanic eruptions have helped illuminate our understanding of: (1) the dispersion and atmospheric fractionation of volcanic ash and (2) the determination of the size and degassing energetics of shallow magma bodies beneath volcanoes

Quaternary tephra of Northern Central America

Silicic Plinian tephra units representing more than 30 Quaternary eruptions blanket Guatemala and El Salvador. They were erupted mainly from 5 principal sources, all of them calderas. Several of the eruptions were accompanied by ash flows. These eruptions also have the most extensive tephra deposits. The total volume of material erupted is equivalent to 300–500 km3 of dense rock. A major uncertainty is the volume of tephra scattered very far from the source. The volume of silicic magma erupted in the Quaternary is similar to the volumes of mafic lava produced at the volcanic front. The basaltic and andesitic cones of the volcanic front parallel the offshore Middle America trench and the active underthrust zone. The five caldera sources form a trend parallel to the volcanic front, on the side opposite the trench, where the older continental crust abuts the volcanic zone. The ages of silicic volcanism precede and overlap with the age of mafic volcanic front, which is largely younger than 50,000 years. All of the calderas have multiple eruptions which span at least many tens of thousands of years. Between the calderas the interfingering of ashes has allowed a network of relative ages to be established. We used a variety of techniques to characterize these units. They can be readily distinguished from units from many other provinces, but considerable effort is required to distiguish among the local units. Standard field and petrographic observations (stratigraphic data, thicknesses, grain size, lithic content, mineralogy) establish the critical framework which disallows most erroneous correlations. Geochemical analysis, particularly trace elements, provide a rapid means of ruling out many more possible corrections. Qualitative mineralogical analysis by electron microprobe of hornblende and Fe-Ti oxides was a very effective last resort for correlation

Gas emissions and the eruptions of mount St. Helens through 1982

The monitoring of gas emissions from Mount St. Helens includes daily airborne measurements of sulfur dioxide in the volcanic plume and monthly sampling of gases from crater fumaroles. The composition of the fumarolic gases has changed slightly since 1980: the water content increased from 90 to 98 percent, and the carbon dioxide concentrations decreased from about 10 to 1 percent. The emission rates of sulfur dioxide and carbon dioxide were at their peak during July and August 1980, decreased rapidly in late 1980, and have remained low and decreased slightly through 1981 and 1982. These patterns suggest steady outgassing of a single batch of magma (with a volume of not less than 0.3 cubic kilometer) to which no significant new magma has been added since mid-1980. The gas data were useful in predicting eruptions in August 1980 and June 1981

Ash and sulfur dioxide in the 2008 eruptions of Okmok and Kasatochi: Insights from high spectral resolution satellite measurements

Ash particles and sulfur dioxide gas are two significant components of volcanic clouds that are important because of their effects on the atmosphere. Several different satellite instruments are capable of delivering quantitative measurements of ash and SO2, but few can provide simultaneous assessments. High-spectral resolution (ν/Δν ∼ 1200) infrared satellite data from the Atmospheric Infrared Sounder (AIRS) are utilized to detect volcanic ash within the 8-12 μm window region, and at the same time exploit the 4.0 μm and 7.3 μm bands of SO2 to detect SO 2 at two different heights. The purpose is to study the interaction between gas and particles in dispersing volcanic clouds, and investigate the circumstances when the gas-rich and ash-rich parts of the plume are collocated and when they separate. Simultaneous retrievals of ash and SO2 in the eruption clouds from Okmok and Kasatochi suggest that the two components were transported together for at least the first 3 days after the initial injection. Later (several days) transport is difficult to infer because of the lack of sensitivity of the ash algorithm to thin, dispersing ash clouds. For Kasatochi and Okmok, AIRS measured maximum masses of approximately 1.21 ± 0.01 Tg and 0.29 ± 0.01 Tg of SO2, and 0.31 ± 0.03 Tg and 0.07 ±0.03 Tg of fine ash (1 μm < radii < 10 μm), respectively. The retrieval schemes described here are capable of detecting the distribution of SO2 simultaneously with estimates of ash concentrations from the same satellite instrument and represent an important improvement for observations of multispecies dispersing volcanic clouds. Analyses of other volcanic eruptions show that SO2 and ash do not always travel together. Consequently, it is concluded that for dispersing volcanic clouds it is vital to be able to detect both SO2-rich and ash-rich clouds simultaneously in order to diagnose their effect on the atmosphere and the aviation hazard. © 2010 by the American Geophysical Union.SCOPUS: ar.jinfo:eu-repo/semantics/publishe