Simulated effect of a forest road on near‐surface hydrologic response: redux

In the work reported here the comprehensive physics‐based Integrated Hydrology Model (InHM) was employed to conduct both three‐ and two‐dimensional (3D and 2D) hydrologic‐response simulations for the small upland catchment known as C3 (located within the H. J. Andrews Experimental Forest in Oregon). Results from the 3D simulations for the steep unchannelled C3 (i) identify subsurface stormflow as the dominant hydrologic‐response mechanism and (ii) show the effect of the down‐gradient forest road on both the surface and subsurface flow systems. Comparison of the 3D results with the 2D results clearly illustrates the importance of convergent subsurface flow (e.g. greater pore‐water pressures in the hollow of the catchment for the 3D scenario). A simple infinite‐slope model, driven by subsurface pore‐water pressures generated from the 3D and 2D hydrologic‐response simulations, was employed to estimate slope stability along the long‐profile of the C3 hollow axis. As expected, the likelihood of slope failure is underestimated for the lower pore pressures from the 2D hydrologic‐response simulation compared, in a relative sense, to the higher pore pressures from the 3D hydrologic response simulation. The effort reported herein provides a firm quantitative foundation for generalizing the effects that forest roads can have on near‐surface hydrologic response and slope stability at the catchment scale. Copyright © 2006 John Wiley & Sons, Ltd.     

Glycol Ethers As Groundwater Contaminants

Ether derivatives of dihydroxy alcohols, which are formed from ethylene or propylene, comprise an important group of groundwater contaminants known as glycol ethers. Compounds in this group are used as solvents, cleaning agents, and emulsifiers in many chemical products and manufacturing operations. Glycol ethers have been associated with a variety of toxic effects, and some compounds in the group are relatively potent teratogens. The limited information available suggests that glycol ethers are contaminants in groundwater, especially in anaerobic plumes emanating from disposal of mixed industrial and household waste. Most methods used to analyze groundwater samples cannot adequately detect 7g/’ (ppb) concentrations of glycol ethers, and the existing methods perform worst for the most widely used and toxic species. A new method capable of analyzing 7g/’ concentrations of glycol ethers was recently developed, and its use is recommended for groundwater samples where glycol ethers are likely to be present. Résumé. Les éthers glycol, polluants des eaux souterraines. Les dérivés d'éther de dihydroxy-alcool, formés à partir de l'éthylène ou du propylène, constituent un important groupe de polluants des eaux souterraines connus sous le nom d'éthers glycol. Les composés de ce groupe sont utilisés comme solvants, comme agents de nettoyage et comme émulsifiants dans de nombreux produits chimiques et dans de nombreux processus de fabrication. Des effets toxiques variés ont été attribués aux éthers glycol et certains des composés sont des agents tératogènes relativement puissants. Les données disponibles, qui sont limitées, indiquent que les éthers glycol sont des polluants communs dans les eaux souterraines, particulièrement dans les panaches anaéorobies émis par les décharges mixtes de déchets industriels et domestiques. La plupart des méthodes d'analyse d'échantillons d'eau souterraine ne sont pas capables de détecter convenablement des concentrations en éthers glycol de l'ordre du 7g/l (ppb); les méthodes actuelles sont médiocres pour doser les espèces toxiques les plus courantes. Une nouvelle méthode permettant de doser des concentrations en éthers glycol de l'ordre du 7 g/l a été récemment mise au point; son utilisation est préconisée pour les échantillons d'eau souterraine contenant des éthers glycol.     

Supernova Sources and the 92Nb-92Zr p-Process Chronometer

We report new Zr isotope evidence for live (92)Nb (mean life: tau&d1;92Nb=52 Myr) within the early solar system resulting in &parl0;92Nb&solm0;93Nb&parr0;initial approximately 10-3. The meteoritic minerals rutile and zircon have, respectively, very high and very low Nb/Zr ratios and are ideal for exploring the (92)Nb-(92)Zr chronometer. Rutiles exhibit high positive straightepsilon92Zr ( approximately 14-36) while a zircon has a negative straightepsilon92Zr ( approximately -4), as would be expected if (92)Nb was live in the early solar system. The meteoritic rutiles appear to be young, with apparent times of formation of approximately 80-220 Myr subsequent to the origin of the solar system. The initial (92)Nb/(92)Mo for the solar system is broadly compatible with a model of uniform production if the (92)Nb/(92)Mo production ratio for Type II supernova (SNII) sources with neutrino-driven winds is used. Data for all the now extinct p-process nuclides ((92)Nb, (97)Tc, and (146)Sm) are consistent with these isotopes being derived by uniform production from SNII sources and a free decay interval of approximately 10 Myr. Consideration of a range of models indicates that the average p-process production ratio of (92)Nb/(92)Mo needs to be at least in the range of 0.06-0.25.     

Pits,rifts and slumps: the summit structure of Piton de la Fournaise

A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island, Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°, normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m. Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve monitoring.     

Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua

 Persistent activity at Masaya Volcano, Nicaragua, is characterised by cycles of intense degassing, lava lake development and pit crater formation. It provides a useful site to study the processes which govern such activity, because of its easy accessibility and relatively short cycles (years to decades). An understanding of the present activity is important because Masaya is visited by large numbers of tourists, is located close to major cities and has produced voluminous lavas, plinian eruptions and ignimbrites in the recent past. We provide structural and geophysical data that characterise the "normal" present state of activity. These indicate that the ongoing degassing phase (1993 to present) was not caused by fresh magma intrusion. It was associated with shallow density changes within the active Santiago pit crater. The activity appears to be associated predominantly with shallow changes in the pit crater structure. More hazardous activity will occur only if there are significant departures from the present gravity, deformation and seismic signatures. Received: 16 May 1997 / Accepted: 29 October 1997     

Interpretation of Nd,Sr and Pb isotope data from Archean migmatites in Lofoten-Vesterålen,Norway

Sm-Nd data for the Archean granulite and amphibolite facies migmatites of Langøy and Hinnøy in Vesterålen are presented which indicate that their protoliths formed ～2.6 AE ago. Rubidium and U loss during a granulite facies metamorphism at ～1.8 AE caused serious disturbance of total-rock U-Pb and Rb-Sr systems. Therefore these systems do not provide any precise age information for the granulite facies migmatites. For the amphibolite facies migmatites of Vesterålen both SmNd, RbSr and PbPb total-rock systems give model ages of ～2.6 AE. The results on both granulite and amphibolite facies rocks are thus in agreement. Previous interpretations based on PbPb data, which indicated an age of 3.41 AE for the Archean terrane of Vesterålen, are not valid.One SmNd model age from the granulite facies migmatites at Moskenesøy in Lofoten indicates that the protoliths of these migmatites formed ～2.0 AE ago and are thus not related to the Vesterålen migmatites.     

Sm-Nd isotopic evolution of chondrites

The¹⁴³Nd/¹⁴⁴Nd and¹⁴⁷Sm/¹⁴⁴Nd ratios have been measured in five chondrites and the Juvinas achondrite. The range in¹⁴³Nd/¹⁴⁴Nd for the analyzed meteorite samples is 5.3 ε-units (0.511673–0.511944) normalized to¹⁵⁰Nd/¹⁴²Nd= 0.2096. This is correlated with the variation of 4.2% in¹⁴⁷Sm/¹⁴⁴Nd (0.1920–0.2000). Much of this spread is due to small-scale heterogeneities in the chondrites and does not appear to reflect the large-scale volumetric averages. It is shown that none of the samples deviate more than 0.5 ε-units from a 4.6-AE reference isochron and define an initial¹⁴³Nd/¹⁴⁴Nd ratio at 4.6 AE of0.505828 ± 9. Insofar as there is a range of values of¹⁴⁷Sm/¹⁴⁴Nd there is no unique way of picking solar or average chondritic values. From these data we have selected a new set of self-consistent present-day reference values for CHUR (“chondritic uniform reservoir”) of (¹⁴³Nd/¹⁴⁴Nd)_CHUR⁰ = 0.511836and(¹⁴⁷Sm/¹⁴⁴Nd)_CHUR⁰ = 0.1967. The new¹⁴⁷Sm/¹⁴⁴Nd value is 1.6% higher than the previous value assigned to CHUR using the Juvinas data of Lugmair. This will cause a small but significant change in the CHUR evolution curve. Some terrestrial samples of Archean age show clear deviations from the new CHUR curve. If the CHUR curve is representative of undifferentiated mantle then it demonstrates that depleted sources were also tapped early in the Archean. Such a depleted layer may represent the early evolution of the source of present-day mid-ocean ridge basalts. There exists a variety of discrepancies with most earlier meteorite data which includes determination of all Nd isotopes and Sm/Nd ratios. These discrepancies require clarification in order to permit reliable interlaboratory comparisons. The new CHUR curve implies substantial changes in model ages for lunar rocks and thus also in the interpretation of early lunar chronology.