Ocean-bottom seismometer observations of seismic activity at Loihi Seamount,Hawaii

This study reports the result of deep ocean-bottom seismometer recording of an undersea volcanic event in progress. An array of five three-component, isolated sensor ocean-bottom seismometers (ISOBS) was deployed for 28 days on the summit and flanks of Loihi Seamount, Hawaii, to monitor seismicity. The deployment was prompted by reports from the Hawaiian Volcano Observatory (HVO) of a swarm of small-magnitude events located beneath the active submarine volcano in late September, 1986. Monitoring of this earthquake swarm by the University of Hawaii commenced 1 October 1986. Although seismicity tapered off rapidly after 11 October, more than 200 events were located. Systematic changes in spatial clustering during the initial swarm activity suggest changing patterns of stress within this crustal volume, possibly due to induced stress resulting from magma movement in the underlying crust or deep portions of the edifice.Most of the very shallow (< 10 km) events were located beneath the summit and southwest flank of the elongate edifice. No shallow tremor was observed despite a search through the data, although such tremor may have ceased prior to deployment of the ocean-bottom seismometers (OBS). Constraints on the association between seismicity and observed topographic and tectonic elements of Loihi are also of primary importance. Many of the earthquakes located near the steep flanks generated rock falls that were recorded on the OBSs. This is consistent with the results of dredge and bottom photography data indicating that the flanks are covered with fragments of shattered lava pillows and flows. Dike intrusion and mass wasting are major influences on the morphology of Loihi. Intact flows have been observed near the deep portion of the south rift zone; however, few events were located in that region during this swarm.     

Copenhagen,Climate Science and the Emotional Geographies of Climate Change

The Pacific island nation-state of Tuvalu featured significantly at the Copenhagen Conference of Parties (COP) 15 climate change negotiations, where the vulnerability of Tuvalu to sea level rise and emotional outpourings of the Tuvaluan delegation contributed to the nation's prominence. In this paper we discuss the likely impacts for Tuvalu of a 1.5°C versus 2°C global warming target and explore sadness and discomfort surrounding discussion of these targets during COP 15. We highlight tensions between science and emotion, arguing that affective encounters can be significant in climate change decision-making. Weeping by a member of the Tuvalu delegation evoked discomfort in the conference plenary. This discomfort briefly unsettled the apparently stable boundaries of convention and protocol that seek to separate emotion from science and politics. We argue that possibilities for change arise when emotions enter climate change negotiations, even though (or perhaps because) these are arenas that privilege rational exchange. Our conclusion urges that more attention be paid to how climate science and emotion are intertwined in climate change politics.     

Determination of heterogeneities in the hydraulic properties of a phreatic aquifer from tidal level fluctuations: a case in Argentina

A well-known analytical solution of Jacob (1950) for groundwater flow due to tidal-wave propagation, together with field measurements along a complete tidal cycle and geological data, were used to evaluate the heterogeneities in the hydraulic properties of a phreatic aquifer located next to the River Ajo in the coastal plain environment of the southern sector of the Samborombon Bay wetland, Argentina. From the analysis of water-table fluctuations in a set of monitoring wells located along a riverbank-normal transect, it was possible to quantify the piecewise spatial variations of the hydraulic diffusivity of the phreatic aquifer. The results show the strong lateral variations of the sedimentary environment due to the influence of the different transport and deposition agents that characterize the coastal plain. The known thickness of the phreatic aquifer and the estimated range of the specific yield allowed the hydraulic conductivity to be identified as the most influential factor. [Jacob CE (1950) Flow of ground water. In: Rouse H (ed) Engineering Hydraulics. Wiley, New York]     

Implications of estimated and measured thermal conductivity for oceanic heat flow studies

Heat flow data provide constraints on the thermal structure and evolution of the oceanic lithosphere. Because precise determination of the heat flux requires that both the thermal gradient and the thermal conductivity be well determined we have examined the thermal conductivities used in a new Pacific Basin heat flow data set. 43% of the 1600 heat flow determinations rely on values estimated by various methods, rather than directly measured. Although the measured and estimated conductivities have comparable means, the measured conductivities have a standard deviation 50% larger than the estimated, suggesting that the estimated values underestimate the actual variation. We investigate the limitations of using such estimates by examining factors controlling the variations of measured conductivity values. We find that the variation between the closest adjacent sites increases with increasing separation, such that sites within 200 km are on average noticeably closer in conductivity than sites further apart. Contributing to this effect may be the variation of conductivity with lithology (with mean conductivity highest for carbonate oozes, intermediate for deep-sea clays, and least for siliceous oozes) and a possible trend of decreasing conductivity with increasing seafloor depth. Tests with the measured data suggest that the best method for estimating conductivity is using the mean value measured within 200 km. The mean of a larger geographical region is a somewhat poorer predictor, and using the oceanwide mean and the value at the nearest site are poorer still. Approximately 29% of the estimated values were not based on measurements from a reference site. For most others, the reference site was the nearest measurement from the same cruise, typically a large distance away. For those sites where conductivity was not measured, 78% had measured conductivity within 200 km and were reestimated using the local mean, whereas the remaining 22% were reestimated using the regional mean. The resulting change in the estimated conductivity averaged 9% using the local mean and 6% using the regional mean. We suggest that such a procedure be used to improve the utility of the heat flow data set, as an alternative to discarding the large fraction of the available data that does not incorporate measured conductivities.     

Great Microwave Bursts and hard X-rays from solar flares

The microwave and hard X-ray characteristics of 13 solar flares that produced microwave fluxes greater than 500 solar flux units have been analyzed. These Great Microwave Bursts were observed in the frequency range from 3 to 35 GHz at Bern, and simultaneous hard X-ray observations were made in the energy range from 30 to 500 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission spacecraft. The principal aim of this analysis is to determine whether or not the same distribution of energetic electrons can explain both emissions. The temporal and spectral behaviors of the microwaves as a function of frequency and the X-rays as a function of energy were tested for correlations, with results suggesting that optically thick microwave emission, at a frequency near the peak frequency, originates in the same electron population that produces the hard X-rays. The microwave emission at lower frequencies, however, is poorly correlated with emission at the frequency which appears to characterize this common source. A single-temperature and a multitemperature model were tested for consistency with the coincident X-ray and microwave spectra at microwave burst maximum. Four events are inconsistent with both of the models tested, and neither of the models attempts to explain the high-frequency part of the microwave spectrum. A source area derived on the basis of the single-temperature model agrees to within the uncertainties with the observed area of the one burst for which spatially resolved X-ray images are available.Swiss National Science Foundation Fellow from the University of Bern.Also Energy/Environmental Research Group, Incorporated, Tucson, Arizona, and Department of Physics and Astronomy, University of North Carolina, Chapel Hill. Present address: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland.     

Response of landfill clay liners to extended periods of freezing

This paper presents the results of a physical model study of the performance of landfill clay cover liners subjected to extended freezing periods. Three proposed designs for a prototype cover liner were evaluated with a primary objective being the determination of frost penetration resulting from the sub-freezing temperatures imposed as an upper boundary condition to the model. The ultimate performance of the three liner designs were compared on the basis of frost penetration, leakage through the liner, and frost heave. The observed depth of frost penetration was compared to that predicted using a simplified analytical solution of the thermodynamic problem, in addition to measured field behavior.

The laboratory experiment utilizes a 1.8 m² tank, of ca 2.1 m depth. The tank is loaded with clay to the specifications required for landfill liners. Three different landfill cover liner designs were modeled in the experimental tank. The performance of the three designs, as measured by a variety of observations, were compared. Frost heave was measured for each design and was found to vary between 3.8 and 4.3 cm. The results indicate the depth of frost penetration was similar for all designs tested (29.2–31.7 cm), although the design which included a soil drainage layer had superior leakage performance.     

Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.     

When the earth blisters: Exploring recurrent liquefaction features in the coastal system of Christchurch,New Zealand

The 14 February, or Valentine's Day, 2016 earthquake located offshore of Christchurch produced a new generation of liquefaction in the coastal environment of Christchurch, an environment of recurrent liquefaction during the 2010–2011 Canterbury Earthquake Sequence. The Valentine's Day earthquake occurred while trenches were open at a site in the coastal environment for studying the 2010–2011 liquefaction features. Observations in the 2016 trenches provided insights into the formation of a suite of surface and subsurface liquefaction features characteristic of the dune deposits, related to the persistent shallow water table, well‐sorted sands within the liquefiable layer and the soil above. Given these conducive conditions, there is a high potential that all earthquakes capable of inducing liquefaction may have been recorded during formation of the dunes near Christchurch. However, overprinting by subsequent generations of liquefaction features may be common and present challenges in unravelling the event history.     

Gyldén systems: Rotation of pericenters

A canonical transformation in phase space and a rescaling of time are proposed to reduce a Keplerian system with a time-dependent Gaussian parameter to a perturbed Keplerian system with a constant Gaussian parameter. When the time variation is slow, the perturbation through second order in the reduced problem is conservative, and, as a result, the orbital space of the averaged system is a sphere on which the phase flow causes a differential rotation representing a circulation of the line of apsides. The flow presents two isolated singularities corresponding to circular orbits travelled respectively in the direct and in the retrograde sense, and a degenerate manifold of fixed points corresponding to the collision orbits. Normalization beyond order two does not break the degeneracy. Adiabatic invariants, which are conservative functions, may be computed from the normalized Hamiltonian evaluated here to the fourth order. Nonetheless so high an approximation gives little information because the normalizing Lie transformation depends explicitly on the time through mixed secular-periodic terms. As an application, an estimate is offered for the apsidal rotation that a second order time derivative in the mass of the sun would induce on planetary orbits. This suggests an observational method for determining the latter parameter for the solar wind, but the predicted motions are too slow for the current level of observational precision.