The history and dynamics of a welded pyroclastic dam and its failure

Igneous intrusions in coal seams are found in 80 % of coal mines in the Huaibei coalfield, China, and coal and gas outburst accidents have occurred 11 times under a 120-m-thick sill in the Haizi mining field. The magma’s heat had a significant controlling effect on coal seam gas occurrence. Based on theoretical analysis, experimental tests and site validation, we analyzed the temperature distribution following magma intrusion into coal measure strata and the variations in multiple physical parameters and adsorption/desorption characteristics between the underlying coal seams beneath the sill in the Haizi mining field and coal seams uninfluenced by magma intrusion in the adjacent Linhuan mining field. The research results show that the main factors controlling the temperature distribution of the magma and surrounding rocks in the cooling process include the cooling time and the thickness and initial temperature of the magmatic rock. As the distance from sill increases, the critical effective temperature and the duration of sustained high temperatures decrease. The sill in the Haizi mining field significantly promoted coal seam secondary hydrocarbon generation in the thermally affected area, which generated approximately 340 m³/t of hydrocarbon. In the magma-affected area, the metamorphic grade, micropore volume, amount of gas adsorption, initial speed of gas desorption, and amount of desorption all increase. Fluid entrapment by sills usually causes the gas pressure and gas content of the underlying coal seams to increase. As a result, the outburst risks from coal seams increases as well.     

Geologic and hydrologic settings for development of freshwater lenses in arid lands

Satellite observations were used to test the validity of previously identified favourable conditions for the formation of freshwater lenses, identify additional potential occurrences, and model modern potential recharge in the Raudhatain Watershed (3696) in northern Kuwait. Favourable conditions include infrequent yet intensive precipitation events, drainage depressions to collect the limited runoff, and presence of conditions (e.g. high infiltration capacity) that promote groundwater recharge and preservation (e.g. underlying saline aquifer) of infiltrating groundwater as freshwater lenses floating over saline aquifer water due to differences in density. Specifically, the following field and satellite‐based observations were noted for the Raudhatain Watershed: (1) Over ~30 precipitation events were identified from the Tropical Rainfall Measuring Mission precipitation data (1998–2009); (2) slope is gentle (2 m/km), and the surface is largely (80%) covered by alluvial deposits with high infiltration capacities (up to 9 m/day); (3) no flows and long‐term ponding were reported at the watershed outlet or detected from Landsat thematic mapper images; (4) infiltration is high based on increases in soil moisture content (from an advanced microwave scanning radiometer) and vegetation index following large precipitation events; and (5) freshwater lenses that overlie highly saline [total dissolved solids (TDS): >35 000] unconfined aquifers underlying the watershed are absent in the southern regions, where infiltrating fresh water mixes with the less saline groundwater (TDS: <10 000). Twenty potential locations (size: 1 to 75 km²) for freshwater lens development were identified in northern Kuwait, and continuous rainfall–runoff models (Soil Water and Assessment Tool) were applied to provide a first‐order estimation of the average annual recharge in the watershed (127 × 10⁶ m³) and freshwater lenses (8.17 × 10⁶ m³). Results demonstrate the settings for enhanced opportunities for groundwater recharge, outline the amounts of and preservation conditions for the groundwater feeding the freshwater lenses, and highlight potential applications and locations of freshwater lenses in similar settings elsewhere in the Arabian Peninsula and beyond. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of watershed land use on sources and nutritional value of particulate organic matter in temperate headwater streams

Suspended particulate organic matter (POM) in headwater streams is an important source of food and energy to stream food webs. In order to determine the effects of watershed land use on the sources and characteristics of POM, we compared the lipid composition of POM (fatty acid, aliphatic alcohol and sterol) from streams influenced by different types of watershed land use. Eight first-order streams discharging to the York River Estuary (Virginia, USA) were sampled during baseflow conditions bi-monthly from February to November 2009, including streams draining forest-dominated, pasture-dominated, cropland-dominated, and urban land-dominated watersheds. Allochthonous vs. autochthonous lipids showed that POM in most of these streams was dominated by allochthonous sources (59.5 ± 14.2 vs. 39.6 ± 14.5 % for aliphatic alcohols and 52.9 ± 11.5 vs. 34.1 ± 10.3 % for sterols). The relative abundance of allochthonous vs. autochthonous lipid inputs to POM varied as a function of land use type. POM in streams draining forest-dominated watersheds contained a higher proportion of allochthonous lipids and a lower proportion of autochthonous lipids than the streams influenced by human land use. The contribution of bacterial fatty acids differed significantly among sampling times (P = 0.003), but not among land use types (P = 0.547). Stepwise linear regression model selected nitrate and temperature as the best predictors of variation in bacterial inputs to POM. Proxies used to assess the nutritional value of POM potentially available to stream consumers included C:N ratios, and the concentrations of total long-chain polyunsaturated fatty acids, eicosapentaenoic acid, arachidonic acid, and cholesterol. None of these nutritional proxies differed among sampling months (P ≥ 0.171), but the proxies showed that the nutritional value of POM in forest streams was lower than in urban streams. Collectively, these findings suggest that human land use in upstream watersheds alters the source composition and nutritional value of stream POM, which not only impacts food quality for stream biota, but also potentially changes the characteristics of OM reaching downstream ecosystems.     

Phosphorus in sediments of high-elevation lakes in the Sierra Nevada (California): implications for internal phosphorus loading

In high-elevation lakes of the Sierra Nevada (California), increases in phosphorus (P) supply have been inferred from changes in phytoplankton growth during summer. To quantify rates of sediment P release to high-elevation Sierran lakes, we performed incubations of sediment cores under ambient and reducing conditions at Emerald Lake and analyzed long-term records of lake chemistry for Emerald and Pear lakes. We also measured concentrations of individual P forms in sediments from 50 Sierra Nevada lakes using a sequential fractionation procedure to examine landscape controls on P forms in sediments. On average, the sediments contained 1,445 µg P g^?1, of which 5 % was freely exchangeable, 13 % associated with reducible metal hydroxides, 68 % associated with Al hydroxides, and the remaining 14 % stabilized in recalcitrant pools. Multiple linear regression analysis indicated that sediment P fractions were not well correlated with soluble P concentrations. In general, sediments behaved as net sinks for P even under reducing conditions. Our findings suggest that internal P loading does not explain the increase in P availability observed in high-elevation Sierran lakes. Rather, increased atmospheric P inputs and increased P supply via dissolved organic C leaching from soils may be driving the observed changes in P biogeochemistry.     

Aftershock sequence simulations using synthetic earthquakes and rate-state seismicity formulation

We use an efficient earthquake simulator that incorporates rate-state constitutive properties and uses boundary element method to discretize the fault surfaces, to generate the synthetic earthquakes in the fault system. Rate-and-state seismicity equation is subsequently employed to calculate the seismicity rate in a region of interest using the Coulomb stress transfer from the main shocks in the fault system. The Coulomb stress transfer is obtained by resolving the induced stresses due to the fault patch slips onto the optimal-oriented fault planes. The example results show that immediately after a main shock the aftershocks are concentrated in the vicinity of the rupture area due to positive stress transfers and then disperse away into the surrounding region toward the background rate distribution. The number of aftershocks near the rupture region is found to decay with time as Omori aftershock decay law predicts. The example results demonstrate that the rate-and-state fault system earthquake simulator and the seismicity equations based on the rate-state friction nucleation of earthquake are well posited to characterize the aftershock distribution in regional assessments of earthquake probabilities.     

Potential environmental issues of CO2 storage in deep saline aquifers: Geochemical results from the Frio-I Brine Pilot test,Texas, USA

Sedimentary basins in general, and deep saline aquifers in particular, are being investigated as possible repositories for large volumes of anthropogenic CO₂ that must be sequestered to mitigate global warming and related climate changes. To investigate the potential for the long-term storage of CO₂ in such aquifers, 1600 t of CO₂ were injected at 1500 m depth into a 24-m-thick “C” sandstone unit of the Frio Formation, a regional aquifer in the US Gulf Coast. Fluid samples obtained before CO₂ injection from the injection well and an observation well 30 m updip showed a Na–Ca–Cl type brine with ∼93,000 mg/L TDS at saturation with CH₄ at reservoir conditions; gas analyses showed that CH₄ comprised ∼95% of dissolved gas, but CO₂ was low at 0.3%. Following CO₂ breakthrough, 51 h after injection, samples showed sharp drops in pH (6.5–5.7), pronounced increases in alkalinity (100–3000 mg/L as HCO₃) and in Fe (30–1100 mg/L), a slug of very high DOC values, and significant shifts in the isotopic compositions of H₂O, DIC, and CH₄. These data, coupled with geochemical modeling, indicate corrosion of pipe and well casing as well as rapid dissolution of minerals, especially calcite and iron oxyhydroxides, both caused by lowered pH (initially ∼3.0 at subsurface conditions) of the brine in contact with supercritical CO₂.     

Volcano monitoring in NZ and links to SW Pacific via the Wellington VAAC

Monitoring for natural hazards like earthquakes, volcanic eruptions and landslides in New Zealand is under taken by GNS Science through the GeoNet project, funded by the Earthquake Commission (EQC). The volcano monitoring function, which includes seismograph and GPS networks, visual observations, webcams, deformation, gas and chemical measurements, assesses the status of New Zealand’s 12 active volcanoes and disseminates warnings as necessary. Interaction with the Wellington VAAC addresses aviation concerns. Near-real-time data is obtained from the monitoring networks and processed via two data centres, with two Duty Officers who respond to pager alerts. Through the National Civil Defence Plan, the volcano monitoring function is delegated to GNS Science, which is responsible for setting the volcanic alert level at each volcano. The Alert level is then used by responding agencies, industries, utility providers and the public to set their response. The New Zealand alert level system is based on the current status of the volcano, and is not necessarily predictive. The aviation industry is one of these responding industries. As a consequence of the 1995 and 1996 eruptions of Ruapehu volcano, it became apparent that the aviation industry required more information than the standard VAAC data and an additional service known as VAAS (NZ Volcanic Ash Advisory System) was established by MetService NZ and GNS Science. This arrangement provides enhanced services to the airlines and ensures rapid dissemination and quantification of information like SIGMET and NOTAM. GNS Science has informal relationships with similar geological based organisations in SW Pacific countries, especially Vanuatu and the Solomon Islands, and is able to quantify information about eruptions in those countries. Similarly, MetService NZ has relationships and is able to obtain pilot reports and updates from the meteorological and air traffic control organisations.     

Mn-oxides and sequestration of heavy metals in a suburban catchment basin of the Chesapeake Bay watershed

The Chesapeake Bay is greatly impacted by numerous pollutants including heavy metals and understanding the controls on the distribution of heavy metals in the watershed is critical to mitigation and remediation efforts in controlling this type of pollution. Clasts from a stormwater catchment basin draining a subdivision near George Mason University, Fairfax VA (38°50.090°N 78°19.204°W) were investigated using X-ray diffraction (XRD), Scanning electron microcopy (SEM) and energy dispersive spectroscopy (EDS) to determine the nature of Mn-oxide coatings and relationship to bound heavy metals. Mn-oxides are poorly crystalline and occur as subhedral to anhedral platy particles and more rarely as euhedral plates. Micronodules are a commonly observed texture. Chemical compositions of coatings are variable with average major constituent concentrations being Mn (33.38 wt%), Fe (11.88 wt%), Si (7.33 wt%), Al (5.03 wt%), and Ba (0.90 wt%). Heavy metals are found in the coatings with Zn being most prevalent, occurring in approximately 58% of analyses with an average concentration of (0.66 wt%). Minor amounts of Co, Ni, Pb, and Cl are observed. Heavy metals and Cl are interpreted as being derived from road pollution. Mn-oxides can serve as a sequestration mechanism for pollution but may also release heavy metals. Field and laboratory observations indicate Mn-oxides occurring on the surface of the clasts can be mechanically mobilized. This is a mechanism for transporting heavy metals into the Chesapeake Bay watershed. Deicing agents may serve as a mechanism to release heavy metals through cation exchange and increased ionic strength. This is the first detailed mineralogical investigation of Mn-oxides and the roles they may play in pollution in the Chesapeake Bay.     

A large sedimentary basin in the Terra Sirenum region of the southern highlands of Mars

Different lines of evidence point to hydrological cycling in the martian past. The extent, duration, and magnitude of this cycling remains unclear, as well as the magnitude of aqueous processes on the surface. Here, we provide geomorphic and mineralogic evidence of a large inter-crater sedimentary basin located in the Terra Sirenum region, which was once covered by a body of liquid water with an areal extent of at least 30,000 km² and a depth of approximately 200 m. The topographic basin, which is modified by a number of large impact craters, is partly controlled by ancient impact and tectonic structures. As a result of evaporation of the large body of water, salt flats formed in the lowest topographic reaches of the basin. Hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits. Crater statistics place the maximum age of aqueous activity during the Late Noachian epoch. The relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient Noachian Period when conditions were seemingly more conducive to life.     

Development of an observational error model

In calculating the orbit of a minor planet with a least-squares algorithm, current practice is to assume that all observations of a given era have the same uncertainty, and that the errors in these observations are uncorrelated. These assumptions are unrealistic; and they lead to sub-optimal orbits.Our objective is to develop and validate an observational error model that provides realistic estimates of the uncertainties and correlations in asteroid observations. When used to populate the covariance matrix of the least-squares algorithm, the resulting orbits are shown to more accurately and precisely represent asteroid trajectories.