Collapsing volcanoes: the sleeping giants' threat

Dormant volcanoes are typically thought of as relatively safe environments to live around. However, under certain geological conditions, such volcanoes can be prone to collapse and may generate massive rockslide avalanches reaching tens of kilometres from the volcano.     

The dissociation of OH and OD in comets by solar radiation

The radiative lifetimes of cometary OH are calculated as a function of the heliocentric velocity of the comet and the velocity distributions of the product atoms are determined. At a distance of 1 AU from the Sun, the lifetimes vary between 1.2×10⁵ and 1.9×10⁵ sec at solar minimum and between 1.0×10⁵ and 1.4×10⁵ sec at solar maximum, depending upon velocity. Continuous absorption into the repulsive 1²Σ^- state is major destruction path. The calculated lifetimes are generally consistent with the lifetimes inferred from observations, but suggest some elaboration of the models is necessary. Photodissociation of OH produces a low-velocity component of hydrogen atoms at 8 km sec^?1 relative to the parent OH molecule and a high-velocity component between 17 and 27 km sec^?1. Photodissociation of OH leads to metastable O(¹D) and O(¹S) and is an additional source of the red and green line emission of atomic oxygen. The lifetime of OD is estimated to be about 4.3× 10⁵ sec at solar minimum and 2.6×10⁵ sec at solar maximum so that the OD/OH ratio in comets is enhanced relative to the HDO/H₂O production ratio by a factor between 2 and 3. Photodissociation of OD produces only high-velocity D atoms with a mean value of 17 km sec^?1.     

Source, attenuation and potential mobility of arsenic at New Britannia Mine, Snow Lake, Manitoba

This study was to investigate the source, mobility and attenuation of As at the New Britannia Mine, Snow Lake, Manitoba. One major source of As contamination was determined to be an arsenopyrite residue stockpile (ARS) containing refractory Au in a waste rock impoundment. It appears that As is still moving through glacial clay at the base of the ARS into a confined aquifer even though the pile was capped in the year 2000. Arsenic is also being mobilized from a deposit of tailings, which formed following spills by previous owners, Nor Acme. Arsenic from the tailings is being mobilized by oxidation of arsenopyrite and reduction of arsenate to the more mobile arsenite by arsenate-reducing bacteria. This contamination is affecting a shallow unconfined aquifer and surface water flowing from the tailings through wetlands towards Snow Lake. Arsenic is being attenuated by adsorption to hydrated ferric oxides (HFO) in the tailings, wetland soils and aquatic plants. Although As in surface water, soils and plants along the flow path from the mine to Snow Lake are above Canadian drinking water guidelines, efficient natural attenuation by HFO in soils and plants of the wetlands have limited the concentration in Snow Lake to below drinking water standards.     

The magnesium and calcium contents of sediments,especially pelites,as a function of age and degree of metamorphism

The silicate and carbonate fraction of 98 non-metamorphic shale samples from the Australian platform and of different geological age were analysed for calcium, magnesium, ferrous iron and carbonate. Cainozoic and Mesozoic shales prove to be essentially calcitic, Cambrian and Proterozoic shales are essentially dolomitic and sideritic. A similar trend of high MgO values can be demonstrated for the silicate fraction of the old shales. Extensive literature study confirms these trends for shales and carbonate rocks from all over the world. Slates, hornfelses and schists are Mg rich and Ca poor, whether young or old.Ronov's model of the evolution of the earth's crust ocean and atmosphere, explaining these trends, is critically reviewed but rejected because of impossible storage problems of calcium in the Proterozoic. The increased magnesium content of the old sediments is explained by calcium carbonate sweating out of the sedimentary column, magnesium introduction from altering volcanic rocks within the sedimentary pile and magnesium introduction from connate brines in sandstones. The increasing calcium content of all kinds of sediments with decreasing age is claimed to be related to preferential weathering of extrusive volcanic rocks and sweating out of calcium carbonate from the sedimentary column.     

Neotectonics of the upper Mississippi embayment

Although the upper Mississippi embayment is an area of low relief, the region has been subjected to tectonic influence throughout its history and continues to be so today. Tectonic activity can be recognized through seismicity patterns and geological indicators of activity, either those as a direct result of earthquakes, or longer term geomorphic, structural, and sedimentological signatures. The rate of seismic activity in the upper Mississippi embayment is generally lower than at the margins of tectonic plates; the embayment, however, is the most seismically active region east of the Rocky Mountains, with activity concentrated in the New Madrid seismic zone. This zone produced the very large New Madrid earthquakes of 1811 and 1812.

Geological and geophysical evidence of neotectonic activity in the upper Mississippi embayment includes faulting in the Benton Hills and Thebes Gap in Missouri, paleoliquefaction in the Western Lowlands of Missouri, subsurface faulting beneath and tilting of Crowley's Ridge in northeastern Arkansas and southeastern Missouri, subsurface faulting along the Crittenden County fault zone near Memphis, Tennessee, faulting along the east flank of the Tiptonville dome, and numerous indicators of historic and prehistoric large earthquakes in the New Madrid seismic zone.

Paleoearthquake studies in the New Madrid seismic zone have used trenching, seismic reflection, shallow coring, pedology, geomorphology, archaeology, and dendrochronology to identify and date faulting, deposits of liquefied sand, and areas of uplift and subsidence. The cause of today's relatively high rate of tectonic activity in the Mississippi embayment remains elusive. It is also not clear whether this activity rate is a short term phenomenon or has been constant over millions of years. Ongoing geodetic and geological studies should provide more insight as to the precise manner in which crustal strain is accumulating, and perhaps allow improved regional neotectonic models.     

Space-time ray method for seismic wave fields

Summary The space-time ray method can be applied to the evaluation and continuation (extrapolation) of the complete seismic wave field in laterally inhomogeneous media with curved interfaces. The wave field propagates along certain space-time curves, called space-time rays. Their space projections correspond to standard rays. Examples of possible applications of the space-time ray method, where the standard ray method fails, are as follows: a) The propagation of seismic waves in slightly dissipative media, b) The computation of seismic wave fields generated by seismic sources with direction-dependent source-time variations. c) Downward continuation of the seismic wave field (actual seismograms) measured at the Earth's surface.     

Librations of the Galilean satellites: The influence of global internal liquid layers

The four Galilean satellites are thought to harbor one or even two global internal liquid layers beneath their surface layer. The iron core of Io and Ganymede is most likely (partially) liquid and also the core of Europa may be liquid. Furthermore, there are strong indications for the existence of a subsurface ocean in Europa, Ganymede, and Callisto. Here, we investigate whether libration observations can be used to prove the existence of these liquid layers and to constrain the thickness of the overlying solid layers. For Io, the presence of a small liquid core increases the libration of the mantle by a few percent with respect to an entirely solid Io and mantle libration observations could be used to determine the mantle thickness with a precision of several tens of kilometers given that the libration amplitude can be measured with a precision of 1 m. For Europa, Ganymede, and Callisto, the presence of a water ocean close to the surface increases by at least an order of magnitude the ice shell libration amplitude with respect to an entirely solid satellite. The shell libration depends essentially on the shell thickness and to a minor extent on the density difference between the ocean and the ice shell. The possible presence of a liquid core inside Europa and Ganymede has no noticeable influence on their shell libration. For a precision of several meters on the libration measurements, in agreement with the expected accuracy with the NASA/ESA EJSM orbiter mission to Europa and Ganymede, an error on the shell thickness of a few tens kilometers is expected. Therefore, libration measurements can be used to detect liquid layers such as Io’s core or water subsurface oceans in Europa, Ganymede, and Callisto and to constrain the thickness of the overlying solid surface layers.     

Uranium-thorium systematics of two Canadian coals

A detailed study of U-Th distribution in two Lower Cretaceous coals in Canada shows that for these coals formed in a continental fluvial and deltaic environment with no marine influence, the U contents are in the range 0.07–7.5 ppm with Th in the range 0.3–11.0 ppm. Average Th/U ratios are near 2 which indicates slight uranium enrichment. The environments of the two coals show different degrees of weathering (montmorillonite-illite and kaolin-gibbsite) and U values are lowest in the more weathered environment In sedimentary profiles associated with the coals, the maximum uranium values are not in the coals but in carbonaceoss clay sediments above and below coal seams. Uranium distribution patterns can be correlated cith Ni, Cu, Rb, Pb, Sr, and Zr, indicating contributions from heavy minerals plus more mobile species (possibly simple organic compounds) which are adsorbed or bonded onto claysor organic matter.     

Artificial Sweeteners in a Large Septic Plume

Four artificial sweeteners, acesulfame, sucralose, cyclamate, and saccharin were detected in a large septic plume at Long Point, Ontario, Canada. The pattern of sweetener detections in the groundwater indicated that they were derived from waste water seepage from a large septic system at the site. Acesulfame was pervasive in the septic plume, whereas the other three sweeteners have been attenuated, probably by microbial degradation.     

The role of carbon plantations in mitigating climate change: potentials and costs

A methodology is presented to construct supply curves and cost–supply curves for carbon plantations based on land-use scenarios from the Integrated Model to Assess the Global Environment (IMAGE 2). A sensitivity analysis for assessing which factors are most important in shaping these curves is also presented. In the IPCC SRES B2 Scenario, the carbon sequestration potential on abandoned agricultural land increases from 60 MtC/year in 2010 to 2,700 MtC/year in 2100 for prices up to 1,000 $/tC, assuming harvest when the mean annual increment decreases and assuming no environmental, economical or political barriers in the implementation-phase. Taking these barriers into consideration would reduce the potential by at least 60%. On the other hand, the potential will increase 55 to 75% if plantations on harvested timberland are considered. Taking into account land and establishment costs, the largest part of the potential up to 2025 can be supplied below 100 $/tC (In this article all dollar values are in US dollars of 1995, unless indicated otherwise.). Beyond 2050, more than 50% of the costs come to over 200 $/tC. Compared to other mitigation options, this is relative cheap. So a large part of the potential will likely be used in an overall mitigation strategy. However, since huge emission reductions are probably needed, the relative contribution of plantations will be low (around 3%). The largest source of uncertainty with respect to both potentials and costs is the growth rate of plantations compared to the natural vegetation.