Using GIS and streamlined landforms to interpret palaeo‐ice flow in northern Iceland

The properties of streamlined glacial landforms and palaeo‐flow indicators in the valleys of Viðidalur, Vatnsdalur and Svínadalur in northern Iceland were quantified using spatial analyses. Drumlins and mega‐scale glacial lineations (MSGL) were visually identified using satellite imagery from Google Earth, the National Land Survey of Iceland (NLSI) Map Viewer and Landsat satellites, and using aerial photographs from the NLSI. A semi‐automated technique was developed using ENVI to determine regions in northern Iceland likely to contain streamlined landforms. The outlines of the identified landforms were manually delineated in Google Earth, and all analyses were conducted in ArcGIS using a 20 m digital elevation model (DEM) of Iceland from the NLSI. Smaller features such as flutes, grooves and striations were measured in the field. At least 543 drumlins and 90 MSGL were identified in the three valleys. Average elongation ratios for Viðidalur, Vatnsdalur and Svínadalur are 4.3:1, 5.2:1 and 6.7:1, respectively. The average density of streamlined landforms is 2.34 landforms per 1 km². Striations and orientation data of the drumlins and MSGL demonstrate ice flow to the northwest into Húnaflói. Parallel conformity is higher in the valley of Svínadalur (9° standard deviation) than in Viðidalur (12°) and Vatnsdalur (16°). Packing values are generally higher in the centre of each valley. The properties of streamlined landforms in the valleys of Viðidalur, Vatnsdalur and Svínadalur support the presence of palaeo‐ice stream activity on northern Iceland. Palaeo‐ice streams flowed from these regions into Húnaflói, supplying ice to the margin of the Iceland Ice Sheet during the Last Glacial Maximum. These palaeo‐ice streams provide a mechanism for ice centres from the mainland of Iceland to reach the shelf‐slope break.     

On the warm/cold regime shift in the South China Sea: Observation and modeling study

Remote sensing data sets and a high-resolution three-dimensional regional ocean model were utilized to investigate the shifting of warm/cold regime and the associated sea level variation in the South China Sea (SCS) during 2000–2003. Both the altimetry data and the model results showed an increase in the sea level (warm phase) followed by an abrupt decrease (cold phase) in the SCS during 2000–2003. Heat budget calculations performed with the model revealed excess heat advection from the western Pacific warm pool into the SCS during the warm phase than the cold phase. The warm phase, which occurred during La Niña episodes, resulted from the intrusion of abnormally warmer western Pacific water that increased the heat content and thus sea level in the SCS. The cold phase, which occurred during El Niño episodes, was triggered by a reduction in the net atmospheric heat flux followed by cold water advection into the SCS. Decrease in the rate of precipitation minus evaporation (P?E) also accounted for the falling of sea level during cold phase. The present study integrated the available remote sensing data and advanced numerical model to identify the time-dependent three-dimensional dynamic and thermodynamic forcing that are important in governing the warm/cold regime shift in the SCS.     

Laboratory study of self-potential signals during releasing of CO2 and N2 plumes

Carbon Capture Sequestration (CCS) projects require, for safety reasons, monitoring programmes focused on surveying gas leakage on the surface. Generally, these programmes include detection of chemical tracers that, once on the surface, could be associated with CO₂ degassing. We take a different approach by analysing feasibility of applying electrical surface techniques, specifically Self-Potential. A laboratory-scale model, using water-sand, was built for simulating a leakage scenario being monitored with non-polarisable electrodes. Electrical potentials were measured before, during and after gas injection (CO₂ and N₂) to determine if gas leakage is detectable. Variations of settings were done for assessing how the electrical potentials changed according to size of electrodes, distance from electrodes to the gas source, and type of gas. Results indicated that a degassing event is indeed detectable on electrodes located above injection source. Although the amount of gas could not be quantified from signals, injection timespan and increasing of injection rate were identified. Even though conditions of experiments were highly controlled contrasting to those usually found at field scale, we project that Self-Potential is a promising tool for detecting CO₂ leakage if electrodes are properly placed.     

History of plains resurfacing in the Scandia region of Mars

We present a preliminary photogeologic map of the Scandia region of Mars with the objective of reconstructing its resurfacing history. The Scandia region includes the lower section of the regional lowland slope of Vastitas Borealis extending about 500–1800 km away from Alba Mons into the Scandia sub-basin below ?4800 m elevation. Twenty mapped geologic units express the diverse stratigraphy of the region. We particularly focus on the materials making up the Vastitas Borealis plains and its Scandia sub-region, where erosional processes have obscured stratigraphic relations and made the reconstruction of the resurfacing history particularly challenging. Geologic mapping implicates the deposition, erosion, and deformation/degradation of geologic units predominantly during Late Hesperian and Early Amazonian time (～3.6–3.3 Ga). During this time, Alba Mons was active, outflow channels were debouching sediments into the northern plains, and basal ice layers of the north polar plateau were accumulating. We identify zones of regional tectonic contraction and extension as well as gradation and mantling. Depressions and scarps within these zones indicate collapse and gradation of Scandia outcrops and surfaces at scales of meters to hundreds of meters. We find that Scandia Tholi display concentric ridges, rugged peaks, irregular depressions, and moats that suggest uplift and tilting of layered plains material by diapirs and extrusion, erosion, and deflation of viscous, sedimentary slurries as previously suggested. These appear to be long-lived features that both pre-date and post-date impact craters. Mesa-forming features may have similar origins and occur along the southern margin of the Scandia region, including near the Phoenix Mars Lander site. Distinctive lobate materials associated with local impact craters suggest impact-induced mobilization of surface materials. We suggest that the formation of the Scandia region features potentially resulted from crustal heating related to Alba Mons volcanism, which acted upon a sequence of lavas, outflow channel sediments, and polar ice deposits centered within the Scandia region. These volatile-enriched sediments may have been in a state of partial volatile melt, resulting in the mobilization of deeply buried ancient materials and their ascent and emergence as sediment and mud breccia diapirs to form tholi features. Similar subsurface instabilities proximal to Alba Mons may have led to surface disruption, as suggested by local and regional scarps, mesas, moats, and knob fields.     

Role of permeability barriers in alluvial hydromorphic palaeosols: The Eocene Pondaung Formation,Myanmar

This study examines the lateral distribution of hydromorphy in the fine‐grained alluvial deposits of the Eocene Pondaung Formation, central Myanmar. Through detailed outcrop analysis and using a combined sedimentological and pedological approach, this study proposes a reconstruction of Pondaung overbank floodplain palaeoenvironments. The variations of hydromorphic features in the different overbank sub‐environments are then discussed and used to build a model of hydromorphic variability in alluvial deposits. Two main architectural associations with distinctive lithofacies and pedogenic features were identified, corresponding to different sub‐environments: heterolithic deposits and extensive mudstone successions. The heterolithic deposits display variegated fine‐grained lithofacies and contain poorly developed palaeosols with gley and vertic features, which are interpreted to reflect a seasonal wetlands landscape, developed in actively aggrading avulsion belts. Extensive mudstone successions with Vertisols that locally exhibit mukkara‐style pseudogley features are interpreted to represent a distal open‐forested environment. The palaeosols of both sub‐environments display dense local hydromorphic variations they are also characterized by a gradual shift from gley‐dominated to pseudogley‐dominated features with increasing distance from the avulsion belt. The clay‐dominated lithology of the floodplain parent material, which forms numerous subsurface permeability barriers, is shown to have acted as a fundamental control in limiting water‐table dynamics in coarse‐grained parts of the succession, thereby favouring hydromorphic variability. Palaeosol sequences of the Pondaung Formation contrast with the soil‐landscape associations described in other studies and provide an alternative model with which to account for the hydromorphic variability in poorly drained, alluvial soils. The model proposed as an outcome of this study demonstrates that hydromorphic variations can be dramatic in floodplains where permeability barriers are numerous. Further, the model stresses the importance of undertaking detailed lateral palaeosol analyses prior to making interpretations regarding hydromorphic variability.     

New data on the age of the installation of Urgonian-type carbonates along the northern Tethyan margin: biostratigraphy of the Chopf Member (Helvetic Alps,eastern Switzerland)

The Chopf Member is a glauconitic, phosphate-bearing succession that occurs in the distal part of the Helvetic Alps (eastern Switzerland). The recent discovery of age-diagnostic ammonites within this horizon allows for its attribution to the lower part of the Gerhardtia sartousiana zone (middle Late Barremian). This new age corresponds to a maximal age for the onset of the Schrattenkalk Fm. in this area, and is coeval with the onset of the Urgonian facies in other parts of the western Tethyan realm. This new age allows also for a more precise dating of Late Barremian ${\delta }^{13}\text{C}$ curves. To cite this article: S. Bodin et al., C. R. Geoscience 338 (2006).     

Design of hail measurement networks*

Abstract

Hail and rain data collected in the National Hail Research Experiment's 1976 dense precipitation network have proved useful in defining the requirements of hail measuring networks. It is shown, at least for the hailstorm of 22 June 1976, that the primary maxima and minima of the spatial distribution of hail mass are revealed by a hailpad spacing of about 4 km, and that increasing detail obtains with smaller spacings until with spacings of 0.4 to 0.8 km finer scale features with dimensions of 1–3 km become defined. Monte‐Carlo and conventional statistical analysis show that the confidence limits on the errer in estimating the true hail mass for a storm increase approximately linearly with the mean spacing of hailpads. For the hailfall of 22 June 1976, there is 90% confidence that the true hail mass is estimated within ± 10% for a hailpad spacing of 1.7 km. Estimates of hail kinetic energy and number of hailstones of this accuracy require that hailpads be approximately 10–20% closer or farther apart, respectively. There is no simple numerical relation between the densities of hailpad and wedge raingauge networks covering the same area such that, if satisfied, the networks would then provide estimates of hail mass and total precipitation of the same accuracy for any storm. There is considerable daily variation in the size of hailswaths and in the spatial distribution of hail mass within them, pointing to the need for a climatological study of these aspects of hailfall to assess properly the requirements that a hail network must meet in a given region.     

Two Years of the STEREO Heliospheric Imagers

Imaging of the heliosphere is a burgeoning area of research. As a result, it is awash with new results, using novel applications, and is demonstrating great potential for future research in a wide range of topical areas. The STEREO (Solar TErrestrial RElations Observatory) Heliospheric Imager (HI) instruments are at the heart of this new development, building on the pioneering observations of the SMEI (Solar Mass Ejection Imager) instrument aboard the Coriolis spacecraft. Other earlier heliospheric imaging systems have included ground-based interplanetary scintillation (IPS) facilities and the photometers on the Helios spacecraft. With the HI instruments, we now have routine wide-angle imaging of the inner heliosphere, from vantage points outside the Sun-Earth line. HI has been used to investigate the development of coronal mass ejections (CMEs) as they pass through the heliosphere to 1 AU and beyond. Synoptic mapping has also allowed us to see graphic illustrations of the nature of mass outflow as a function of distance from the Sun – in particular, stressing the complexity of the near-Sun solar wind. The instruments have also been used to image co-rotating interaction regions (CIRs), to study the interaction of comets with the solar wind and CMEs, and to witness the impact of CMEs and CIRs on planets. The very nature of this area of research – which brings together aspects of solar physics, space-environment physics, and solar-terrestrial physics – means that the research papers are spread among a wide range of journals from different disciplines. Thus, in this special issue, it is timely and appropriate to provide a review of the results of the first two years of the HI investigations.