In situ yield behaviour of a coal pillar

Summary An indication of the complete stress-strain behaviour of coal was obtained through instrumenting a headgate yield pillar and monitoring the changes in vertical and horizontal pillar stress, pillar strain, and roof-floor convergence as a function of time and distance from the moving longwall face. A semiautomated monitoring program was conducted over a 5 month period as the longwall face advanced toward and eventually passed the instrumented pillar. The development of a confined core and yield zone within the pillar was confirmed by the vertical and horizontal stress changes. Thein situ pre-failure (208 to 661 MPa) and post-failure moduli (55 to 208 MPa) of the coal were determined from the change in pillar stress versus pillar strain. Thein situ moduli are an order of magnitude lower than the 3450 MPa, commonly assumed for coal.     

Summer temperature variability across four urban neighborhoods in Knoxville,Tennessee, USA

The urban heat island (UHI) is a well-documented effect of urbanization on local climate, identified by higher temperatures compared to surrounding areas, especially at night and during the warm season. The details of a UHI are city-specific, and microclimates may even exist within a given city. Thus, investigating the spatiotemporal variability of a city’s UHI is an ongoing and critical research need. We deploy ten weather stations across Knoxville, Tennessee, to analyze the city’s UHI and its differential impacts across urban neighborhoods: two each in four neighborhoods, one in more dense tree cover and one in less dense tree cover, and one each in downtown Knoxville and Ijams Nature Center that serve as control locations. Three months of temperature data (beginning 2 July 2014) are analyzed using paired-sample t tests and a three-way analysis of variance. Major findings include the following: (1) Within a given neighborhood, tree cover helps negate daytime heat (resulting in up to 1.19 ^°C lower maximum temperature), but does not have as large of an influence on minimum temperature; (2) largest temperature differences between neighborhoods occur during the day (0.38–1.16 ^°C difference), but larger differences between neighborhoods and the downtown control occur at night (1.04–1.88 ^°C difference); (3) presiding weather (i.e., air mass type) has a significant, consistent impact on the temperature in a given city, and lacks the differential impacts found at a larger-scale in previous studies; (4) distance from city center does not impact temperature as much as land use factors. This is a preliminary step towards informing local planning with a scientific understanding of how mitigation strategies may help minimize the UHI and reduce the effects of extreme weather on public health and well-being.     

Analysis of a fast-spreading rise crest: The East Pacific Rise, 9° to 12° south

The axis of the East Pacific Rise is defined by a topographic block about 15 km wide and 300 to 350 m high which is flanked by abyssal hills 100 to 200 m high and 3 to 5 km wide. These hills often are tilted such that their steep slopes face the axis. An empirical model explaining these features combines axial extrusion to form the central block and rotational faulting to lower the shoulders of the axial block to the regional depth and tilt them outward.The axial block is offset about 10 km left-laterally at 10.0°S and a similar amount right-laterally at 11.5°S. Offsets (or lack of offsets) of young magnetic anomalies indicate that these axial displacements occurred between 1.7 and 0.9 m.y. ago and 0.7 m.y. ago and the present in the north and south. respectively. These small axial offsets are interpreted to be the result of either brief episodes of asymmetric see-floor spreading or discrete jumps in the site of spreading activity. Both axial shifts were to the west; a unidirectional sequence of such shifts occurring at the above rate of one per million years would be difficult to differentiate from true regional asymmetric spreading and might explain that phenomenon on other medium-to fast-spreading rises.Reconnaissance data from the east flank of the East Pacific Rise indicate that spreading activity began on that part of the rise between the 9°S and 13.5°S fracture zones approximately 8.2 m.y. ago when the site of crustal accretion jumped westward from the now dormant Galapagos Rise. Slope change in crust approximately 2 and 6 m.y. old imply faster spreading rates between about 6 and 2 m.y. ago than either before or after that time. Identification and correlation of anomaly 3 allows an estimate of about 90 mm/y for this higher east flank spreading rate. Since 1.7 m.y. ago spreading rates have averaged about 80 mm/y to the west and 77 mm/y to the east.     

Large sand waves on the Atlantic Outer Continental Shelf around Wilmington Canyon,off Eastern United States

New seismic-reflection data show that large sand waves near the head of Wilmington Canyon on the Atlantic Outer Continental Shelf have a spacing of 100–650 m and a relief of 2–9 m. The bedforms trend northwest and are asymmetrical, the steeper slopes being toward the south or west. Vibracore sediments indicate that the waves apparently have formed on a substrate of relict nearshore sediments. Although the age of the original bedforms is unknown, the asymmetry is consistent with the dominant westerly to southerly drift in this area which has been determined by other methods; the asymmetry, therefore, is probably modern. Observations in the sand-wave area from a submersible during August 1975, revealed weak bottom currents, sediment bioturbation, unrippled microtopography, and lack of scour. Thus, the asymmetry may be maintained by periodic water motion, possibly associated with storms or perhaps with flow in the canyon head.     

A Method for Installing Piezometers in Large Cobble Bed Rivers

An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies.     

Spatial and temporal variability in the lower food web of the tidal freshwater Hudson River

The mid Hudson River is a heterotrophic system where allochthonous inputs apparently fuel the largest proportion of secondary production and ecosystem metabolism. We have analyzed a 6-yr dataset collected quarterly at six stations spanning a 150-km reach to assess variability at inter- and intra-annual time scales and regional spatial scales. The major components of the lower food web: bacterial biomass, detrital particulate organic carbon (POC), and dissolved organic carbon (DOC), show surprisingly discordant patterns in temporal and spatial variability. Bacterial abundance shows significant variability at all three scales, but the interannual variability is by far the greatest. DOC concentrations showed greatest variability among years, with intra-annual and spatial variability roughly equal. Freshwater flow is commonly considered a major driving force in river-estuarine variability but simple discharge was not a strong predictor of any component of suspended matter or DOC. For organisms in the Hudson River food web, these multiple scales of variability indicate highly unpredictable food resources in time and space, and these fluctuations may contribute to the variability in higher trophic levels.     

Interactions of biogenic opal,sediment and seawater in the Central Equatorial Pacific

The solution rate of biogenic opal in near-surface sediments in the Central Equatorial Pacific is three to eight orders of magnitude lower than similar acid-cleaned samples. Iron, magnesium and calcium aluminosilicates may be the minerals which are forming on the surface of the opal and reducing its solution rate. The scale height of the system studied suggests that diffusive and not advective processes are primarily responsible for the removal of dissolved silica in sediments. Solution budget calculations for this area suggest that 90–99 per cent of the biogenic opal produced in surface waters dissolves before reaching the sediment-water interface; an additional amount dissolves within the sediment and diffuses into bottom waters leaving 0.05–0.15 per cent of the original amount of opal produced by organisms in the sedimentary record. The relative solution potential of the upper 1000 m of the water column varies by more than an order of magnitude from the Antarctic to Equator and may have a pronounced effect on the accumulation rate of biogenic opal in underlying sediments.     

Changes in Arctic clouds during intervals of rapid sea ice loss

We investigate the behavior of clouds during rapid sea ice loss events (RILEs) in the Arctic, as simulated by multiple ensemble projections of the 21st century in the Community Climate System Model (CCSM3). Trends in cloud properties and sea ice coverage during RILEs are compared with their secular trends between 2000 and 2049 during summer, autumn, and winter. The results suggest that clouds promote abrupt Arctic climate change during RILEs through increased (decreased) cloudiness in autumn (summer) relative to the changes over the first half of the 21st century. The trends in cloud characteristics (cloud amount, water content, and radiative forcing) during RILEs are most strongly and consistently an amplifying effect during autumn, the season in which RILEs account for the majority of the secular trends. The total cloud trends in every season are primarily due to low clouds, which show a more robust response than middle and high clouds across RILEs. Lead-lag correlations of monthly sea ice concentration and cloud cover during autumn reveal that the relationship between less ice and more clouds is enhanced during RILEs, but there is no evidence that either variable is leading the other. Given that Arctic cloud projections in CCSM3 are similar to those from other state-of-the-art GCMs and that observations show increased autumn cloudiness associated with the extreme 2007 and 2008 sea ice minima, this study suggests that the rapidly declining Arctic sea ice will be accentuated by changes in polar clouds.     

Trends in marine debris along the U.S. Pacific Coast and Hawai'i 1998-2007

We assessed amounts, composition, and trends of marine debris for the U.S. Pacific Coast and Hawai'i using National Marine Debris Monitoring Program data. Hawai'i had the highest debris loads; the North Pacific Coast region had the lowest debris loads. The Southern California Bight region had the highest land-based debris loads. Debris loads decreased over time for all source categories in all regions except for land-based and general-source loads in the North Pacific Coast region, which were unchanged. General-source debris comprised 30-40% of the items in all regions. Larger local populations were associated with higher land-based debris loads across regions; the effect declined at higher population levels. Upwelling affected deposition of ocean-based and general-source debris loads but not land-based loads along the Pacific Coast. LNSO decreased debris loads for both land-based and ocean-based debris but not general-source debris in Hawai'i, a more complex climate-ocean effect than had previously been found.