Slope inclinometers for landslides

Slope inclinometers/indicators are used to determine the magnitude, rate, direction, depth, and type of landslide movement. This information is usually vitally important for understanding the cause, behavior, and remediation of a landslide. However, many inclinometer measurements fail to achieve these intended aims because of lack of appreciation of the many factors that need to be correctly implemented during installation, monitoring, and data reduction to yield useful data. This paper presents some guidelines for understanding, installing, and interpreting slope inclinometers and presents three case histories that illustrate some of the pitfalls that can develop if these guidelines are not followed.     

Geological Evolution of Longhushan World Geopark in Relation to Global Tectonics

The South China fold belt has experienced a complex series of tectonic events that span 1.0 billion years of earth history. Longhushan (龙虎山) World Geopark is located on the Proterozoic suture between the Yangtze craton and Cathyasia block and highlights the long history of this belt. Collision of the Cathyasia and Yangtze cratons 1.0 billion years ago was associated with the formation of the Rodinian supercontinent where most of the planet's landmasses were amalgamated into one block. Jurassic through Early...     

Body force circulations in a compressible atmosphere: Key concepts

The body force circulation problem of Eliassen is extended to spherical geometry and a quasi-compressible atmosphere using the zonally symmetric tidal theory. The concept of body force circulation is generalized to include the effects of mechanical friction and Newtonian cooling. This viewpoint is conceptually advantageous when the circulation is driven by body forces against radiative relaxation. The resulting linear theory is qualitatively useful in middle atmosphere applications, including the equatorial momentum source for which an analytic solution has not been given previously. Further generalizations of the theory are possible by including dynamical and photochemical feedback effects.     

Atrazine Used as a Tracer of Induced Recharge

The city of Lincoln draws water from a well field along the banks of the Platte River in east-central Nebraska. We have been able to follow the infusion of atrazine into this well field under induced recharge. Samples of water from the river, several monitoring wells and a production well were analyzed by GC/MS and solid phase extraction and found to change in concentration over the range 0.1 and 5.0 ppb of atrazine through the spring, summer, and fall 1989. Increases in the concentration of atrazine relating to precipitation events in the Platte River Basin were observable in the well water samples and ultimately in Lincoln municipal tap water. Atrazine from the river was seen to move via induced recharge and into well field ground water and away from the river at an observable rate. The concentration of atrazine in the river is dependent upon time of year and precipitation in the river basin.     

The Influence of Wellbore Inflow on Electromagnetic Borehole Flowmeter Measurements

This paper describes a combined field, laboratory, and numerical study of electromagnetic borehole flowmeter measurements acquired without the use of a packer or skirt to block bypass flow around the flowmeter. The most significant finding is that inflow through the wellbore screen changes the ratio of flow through the flowmeter to wellbore flow. Experiments reveal up to a factor of two differences in this ratio for conditions with and without inflow through the wellbore screen. Standard practice is to assume the ratio is constant. A numerical model has been developed to simulate the effect of inflow on the flowmeter. The model is formulated using momentum conservation within the borehole and around the flowmeter. The model is embedded in the MODFLOW-2000 ground water flow code.     

Particle fabric in a small, type-2 ignimbrite flow unit (Laacher See, Germany) and implications for emplacement dynamics

 Ignimbrites of the 13-ka Upper Laacher See Tephra were deposited from small, highly concentrated, moderately fluidized pyroclastic flows. Their unconsolidated nature, and the prominence of accidental Devonian slate fragments, make these ignimbrites ideal for clast fabric studies. The upper flow unit of ignimbrite M14 has characteristics typical of a type-2 ignimbrite. Layer 2a and the lower part of layer 2b of the flow unit have strong, upstream-inclined a[p] fabrics (a[p] means long particle axes parallel to flow direction). Only clasts with a/b axial ratios of 2.5 or greater preserve good a[p] fabrics, whereas the a–b planes of flat fragments dip upstream irrespective of axial ratio. The a-axis fabric becomes weaker, flatter, and more girdle-like in the upper half of layer 2b. At one locality the a-axis fabric appears to rotate 40° up through the flow unit, suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base. The existence of similarly strong a[p] fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non-shearing material (layer 2b) on a thin shear layer (layer 2a), and that the entire flow freezes en masse to form the deposit. The data suggest that, if the flow froze en masse, it was shearing pervasively through at least half its thickness. Another possibility is that the flow unit aggraded progressively from the base up, and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition. Received: 13 February 1997 / Accepted: 4 April 1998     

New constraints on the provenance of hopanoids in the marine geologic record: Bacteriohopanepolyols in marine suboxic and anoxic environments

The abundance and structural diversity of bacteriohopanepolyols (BHPs) was examined in three marine pelagic environments that are characterized by strong vertical redox gradients and water column suboxia or anoxia. The abundance and, in most instances, structural diversity of BHPs was highest at depths where conditions were suboxic or anoxic. However, the majority of the BHP structures that were identified are environmentally cosmopolitan and their biological sources are presently not well constrained. An isomer of bacteriohopanetetrol (denoted BHT II) was observed at all three study sites in association with anoxic and suboxic conditions within the water column. Based on the absence of BHT II from terrigenous and oxic marine environments studied to date, and its strong association with suboxic and anoxic marine pelagic environments, we propose that BHT II is a promising candidate biomarker for water column suboxia and anoxia in the marine geologic record. The molecular fingerprint of BHPs in suspended and sinking particles and core-top sediments indicates that hopanoids produced within the water column are exported to marine sediments and that their biological source is most likely associated with settling particles and not the free-water phase. Based on our observations, BHPs likely represent an important input to the sedimentary hopanoid inventory, particularly in upwelling environments characterized by pelagic oxygen minimum zones (OMZ) and anoxic marine basins.     

Isotopic variability in the aragonite shells of freshwater gastropods living in springs with nearly constant temperature and isotopic composition

We conducted a year-long, intensive monitoring program of live aquatic gastropods (Helisoma duryi, Melanoides tuberculata, Physa virgata, Pyrgulopsis sp., and Tyronia sp.) and their host springs in the Ash Meadows National Wildlife Refuge of southern Nevada. Our purpose was to constrain the degree of natural variation in the isotopic values of shell aragonite for gastropods living in near-constant conditions. Inter- and intraspecies variations, as well as within-shell variations, of δ¹⁸O and δ¹³C values for all taxa were larger than predicted based on variations in environmental conditions alone. This result suggests that different organisms growing in identical or nearly identical environmental conditions may not produce shells with equilibrium isotopic compositions and that these offsets from equilibrium may differ by small, but statistically significant amounts. For the gill-breathing, fully aquatic gastropods M. tuberculata, Pyrgulopsis sp., and Tyronia sp., the deviation of measured isotopic values compared to predicted values based on average environmental conditions were consistent with differences between taxa in the seasonal timing of shell growth. Measured values for the lung-breathing gastropods H. duryi and P. virgata were higher for δ¹⁸O and lower for δ¹³C than predicted at isotopic equilibrium, even when accounting for seasonality effects. We suggest that explaining the differences between the shell isotopic composition of lung- and gill-breathing snails requires a combination of both behavioral and physiologic factors. Our results illustrate the potential complexities of interpreting stable isotopic data from fossil gastropod shells even when environmental conditions are nearly constant, and place limitations on the paleoenvironmental deductions that can be made from the isotopic measurements on fossil gastropods.