Boulders and ponds on the Asteroid 433 Eros

There are ∼300 features on the Asteroid 433 Eros that morphologically resemble ponds (flat-floored and sharply embaying the bounding depression in which they sit). Because boulders on Eros are apparently eroding in place and because ponds with associated boulders tend to be larger than ponds without blocks, we propose that ponds form from thermally disaggregated and seismically flattened boulder material, under the assumption that repeated day/night cycling causes material fatigue that leads to erosion of the boulders. Results from a simple boulder emplacement/thermal erosion model with boulders emplaced in a few discrete events (i.e., large impacts) match well the observed size distribution. Under this scenario, the subtle color differences of ponds (somewhat bluer than the rest of the surface) might be due to some combination of less space-weathered material and density stratification of silicate-rich chondrules and more metal-rich matrix from a disaggregated boulder. Volume estimates of ponds derived from NEAR Laser Rangefinder profiles are consistent with what can be supplied by boulders. Ponds are also observed to be concentrated in regions of low slope and high elevation, which suggests the presence of a less mobile regolith and thus a contrast in the resistance to seismic shaking between the pond material and the material that makes up the bounding depression. Future tests include shake-table experiments and temperature cycling (fatigue) of ordinary chondrites to test the thermal erosion mechanism.     

Thermal instability of the fluid column in a borehole: application to the Yaxcopoil hole (Mexico)

Observational evidence proved that even when a borehole is in “fully” stabilized conditions, temperature data may exhibit certain unrest resembling irregular oscillations in the order of hundredths or (in the extreme case) even tenths of degree. Temperature was monitored in complicated hydrogeological conditions in the Yaxcopoil-1 hole (Chicxulub impact structure, Mexico). Two experiments are reported: (a) 20-day monitoring when a logger was located in the center of the high temperature gradient anomaly produced by the cold wave slowly propagating downwards and (b) simultaneous three-loggers 18-day monitoring with loggers located above, in and below the anomaly. All observed temperature–time series displayed intermittent oscillations of temperature with sharp gradients and large fluctuations over all observed time scales. While the “upper” and “lower” records revealed quasi-periodic temperature variations, the “central” record shows fast temperature oscillations with strong up-and-down reversals, all with amplitudes up to a few tenths of degree. The observed temperature–time series were processed by recurrence and recurrence interval quantification as well as by spectral analyses. It is shown that fluid in a borehole, subject to thermal gradient, is stable, as far as the gradient remains below a certain critical value. At higher Rayleigh numbers, the periodic character of oscillations typical for “quiescent” regime is superseded by stochastic features. This “oscillatory” convection occurs due to instability of the horizontal boundary layers. In the specific case of the Yaxcopoil hole, the time series above and below the cold wave (characterized by relatively lower temperature gradients between 20 and 50 mK/m) contain a clear low frequency component produced by tidal forcing. This component dominates over the high frequency domain (periods from 10–15 to 1 min), which exhibit a scaling behavior. This pattern conspicuously changes in the center part of the cold wave, where the local temperature gradient exceeds 200 mK/m and where tidal forcing composes only ~3% of the signal.     

Coronal Magnetic Connectivity and EUV Dimmings

Coronal dimming can be considered to be a disk signature of front-side coronal mass ejections (CMEs) (Thompson et al.: 2000, Geophys. Res. Lett. 27, 1431). The study of the magnetic connectivity associated with coronal dimming can shed new light on the magnetic nature of CMEs. In this study, four major flare-CME events on 14 July 2000, 28 October 2003, 7 November 2004, and 15 January 2005 are analyzed. They were all halo CMEs associated with major flare activity in complex active regions (ARs) and produced severe space weather consequences. To explore the magnetic connectivity of these CMEs, global potential-field extrapolations based on the composite synoptic magnetograms from the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory are constructed, and their association with coronal dimming is revealed by the Extreme ultraviolet Imaging Telescope. It is found that each flare-CME event involved interaction of more than ten sets of magnetic-loop systems. These loop systems occupied over 50% of all identified loop systems in the visible hemisphere and covered a wide range of solar longitudes and latitudes. We categorize the loop systems as active-region loops (ARLs), AR-interconnecting loops (ARILs) including transequatorial loops (TLs), and long arcades (LAs) straddling filament channels. A recurring pattern, the saddle-field configuration (SFC), consisting of ARILs, is found to be present in all four major flare-CME events. The magnetic connectivity revealed by this work implies that intercoupling and interaction of multiple flux-loop systems are required for a major CME. For comparison, a simple flare-CME event of 12 May 1997 with a relatively simple magnetic configuration is chosen. Even for this simple flare-CME event, we find that multiple flux-loop systems are also present.     

Landscape and Coast Development of A Lowland Fjord Margin Following Deglaciation, East Greenland

The landscapes of western Jameson Land bordering Hall Bredning fjord comprise upper river basins, glacial landscapes, lower river basins and a near‐shore zone. The upper river basins are incised into bedrock and display no cover of young sediments whilst the glacial landscapes, located closer to the coast, are dominated by Pleistocene deposits and an irregular topography with hills and ridges. The lower river basins, dissecting the glacial landscapes, are connected to the upper river basins and contain well‐defined Holocene delta terraces. The near‐shore zone, which includes the present coast, displays a few raised shorelines. Geomorphological observations combined with stratigraphic work and ¹⁴C dates provide a chronological framework for the development of landscape and shoreline, as presented by a four‐stage reconstruction. The first stage covers the deglaciation of western Jameson Land at the Weichselian‐Holocene transition after a collapse of the main fjord glacier in Hall Bredning. The sea inundated the low‐lying areas on Jameson Land forming small side‐entry fjord basins that possibly follow the track of older valleys. This was followed by a second stage, the paraglacial period, when large meltwater production and sediment transport resulted in a fast infilling of the side‐entry fjord basins by deltas. These are now exposed in terraces in the lower river basins at 70–80 m a.s.l. During a third stage, the relaxation period, fluvial activity decreased and the land surface was increasingly occupied by a cover of tundra vegetation. A glacio‐isostatic rebound resulted in a relative sea level fall and fluvial incision. During stages two and three the coast was exposed to shallow marine processes that aided the alignment of the coast. Stages one to three presumably lasted for less than 2000 years. During stage four, the stable period, lasting for several thousand years till the present, there were minor adjustments of shoreline and landscape. The four‐step reconstruction describes the sedimentary response of a lowland fjord margin to dramatic changes in climate and sea level. The distribution of erosion and sedimentation during this development was mainly controlled by topography. The reconstruction of the latest environmental development of Jameson Land puts new light on Jameson Land's long and complex Quaternary stratigraphic record. The reconstruction may also be used as a model for the interpretation of deposits in similar areas elsewhere.     

Short-term climate variability and its stochastic modeling

Summary The structure of the temporal variability of temperature records has been investigated by means of different statistical methods including also fractal analysis. Data both from meteorological stations and averaged over wider networks show very similar behaviour; combine a long-run persistence (characterized by a fractal dimension ofD = 1.2–1.3) and short-run properties indicating high year-by-year variability. Synthetic temperature records were created with the use of Mandelbrot's fast fractional Gaussian noise generating algorithm. These fractal sets show the same stochastic properties as real temperature records do, and have even a very similar appearance. The results suggest that the fractal reconstruction algorithm could be used to extrapolate the present tendencies to the future and to forecast future fluctuations.With 8 Figures     

Elasticity of diopside

The thirteen single-crystal elastic moduli for diopside as determined by the acoustic technique based on Brillouin scattering are: c₁₁=2.23, c₂₂=1.71, c₃₃=2.35, c₄₄=0.74, c₅₅=0.67, c₆₆=0.66, c₁₂=0.77, c₁₃=0.81, c₁₅=0.17, c₂₃=0.57, c₂₅=0.07, c₃₅=0.43, c₄₆=0.073. The Reuss bound of the adiabatic bulk and shear moduli calculated from these data are K _s=1.08 Mbar and G=0.651 Mbar. The room-pressure isothermal bulk modulus, K _T , and the pressure derivative of the bulk modulus, K′ _T have also been determined on a four-circle diffractometer, from a single crystal mounted in a gasketed opposed-anvil diamond cell, giving values of K _T =1.13 Mbar and K′ _T =4.8. The principal axes of the strain ellipsoid, calculated from the elastic moduli and observed in the static compression data, are identical, and the linear compressibilities are in reasonable agreement. The single-crystal elastic moduli can be correlated with the structural features of diopside.     

Influence of viscosity on the phase of earth tides

The effect of viscosity on the phase of earth tides is computed. Computations are based on the general theory of the effect of viscosity of the mantle considered as a Maxwell body as it has been elaborated by Molodensky (1963). The problem is solved by the method of variation of constants, starting from the solution for the case of an ideally elastic, spherically symmetrical globe. The computations presented here cover the cases of the earth models B₁ and B₂ of Bullen and Haddon (1967). Love numbers k, l, h were computed for tides of second and third order, and values of phase delay due to viscosity were computed for tides of second order.     

Sustainable Housing Development in Urban Australia: exploring obstacles to and opportunities for ecocity efforts

Basic aspects of sustainable housing design such as increasing density, mixed use and proximity to public transport are being adopted increasingly in Australian cities. Sustainable building codes such as NSW's BASIX and Victoria's Green Star rating systems are also being implemented and advanced. More substantial improvements and endeavours such as onsite food production, energy generation and waste treatment, are being seen increasingly as necessary for urban sustainability, yet little is being done to institutionalise or normalise these through Australia's housing system. Similarly, concerns about the social sustainability of housing identify the need for mixed, flexible tenure and dwelling types, with again little uptake despite evidence of demand. Given that we seem to know what needs doing to move towards sustainability, this paper investigates two ecologically and socially sound community-based housing developments in Australia, with a view to finding what helped or hindered these efforts and what may further the uptake of sustainable design. Assessment of the uptake of sustainable planning initiatives reveals the prevalence of a decidedly neoliberal agenda which shies away from the more substantial challenges ecocity design and community-based enterprise may represent. Such community-based initiatives must, however, be supported at a broader scale, to avoid possible outsourcing of governmental responsibility or the relegation of sustainable design to the sole realm of the wealthy.     

'Muddy glee': rounding out the picture of women and physical geography fieldwork

Fieldwork in geography has come under close scrutiny from feminist and postcolonial scholars in recent years. In relation to physical geography, commentators have pointed to a range of practices and images (notably the 'heroic', masculinist 'ideal') that have acted to deter and exclude women, from undergraduates to senior academics. For some, fieldwork is one of the key sites of gender discrimination for women in physical geography. This paper starts from a position of agreement with many of these critiques, but also seeks to 'reclaim' some more positive accounts and perspectives on the subject. In doing so, it aims to critique and disrupt the dominant image of physical geography fieldwork as essentially a masculinist endeavour, and encourage a wider view of the challenges and pleasures of fieldwork for women in physical geography.     

Evidence of Strain Partitioning Between the Sierra Madre Fault and the Los Angeles Basin, Southern California from Numerical Models

— Geodetic data indicate that the northern Metropolitan Los Angeles region is shortening at a rate of 4.5–6.0 mm/yr between downtown Los Angeles and the San Gabriel Mountains. If we assume that all of the uplift of the San Gabriel Mountains is due to the major frontal fault system (the Sierra Madre fault) and use reported values for bedrock uplift, slip per event and recurrence intervals to determine the slip rate on the Sierra Madre fault, we obtain slip rates between 0.6–1.27 mm/yr. Using these slip rates, the horizontal shortening attributable to the Sierra Madre fault accounts for only ~33% of the observed shortening across the basin, leaving ~67% of the shortening to be accounted for elsewhere. Herein we present a suite of models that test possible shortening mechanisms to account for this strain deficit. The models incorporate a range of fault geometries and have a layered structure with variable vertical and horizontal rheologies. The models demonstrate how lower-crust rheology and the presence of a low rigidity, anelastically deforming sedimentary basin affects the dissipation of stress imposed on the viscous layers by elastic failure of the faults. We found that viscoelastic models with a single fault, vertically strong crust and a compliant sedimentary basin yield a horizontal velocity profile that best matches the geodetically observed velocity profile across the Los Angeles Basin. Our models also indicate that we are still not accounting for all of the observed deformation. Therefore, more complex models that include both laterally varying rheologies and frictional properties on faults must be considered.