The representation and calculation of the deviatoric component of the geological stress tensor

A new diagram for the representation of stress states is proposed and compared with Nadai's stress diagram. The diagram is a graph whose axes are labelled as the differences of the principal stresses (σ₂-σ₃ as ordinate axis, σ₁-σ₂ as the abscissa; where σ₁ > σ₂ > σ₃ are the principal stresses). The design of the plot has been deliberately modelled on that of the ‘log Flinn’ diagram which is used to represent finite strain ellipsoids. The position of the plotted stress state on this diagram depends on the nature of the deviatoric (non-hydrostatic) component of the stress tensor. The distance of the plotted stress from the origin corresponds broadly to the departure of the stress from a hydrostatic state and the parameter R, defined as the gradient of the line joining the plotted state to the origin, expresses the type of symmetry possessed by the stress tensor.It is explained how the diagram can be used to represent calculated palaeostresses and, in particular, how the parameter R can be found directly from some existing methods of stress analysis currently in use.Besides its proposed function to represent the results of such analyses it is felt that the use of the diagram may make clear the essential elements of the definitions of well-known terms used to describe particular stress states (e.g. plane stress, triaxial stress, axial compression, etc.).     

EFFECTS OF DISTANCE INTERNAL TO THE FARM: A CHALLENGING SUBJECT FOR NORTH AMERICAN GEOGRAPHERS*

The effects of intra-farm distance on farm income have not been previously tested in North America. European studies are inconclusive as they use data taken from bookkeeping accounts for the farm as a whole. This paper calls for field-to-field farm analyses that combine internal movement costs with costs of production, yields, and farm-gate prices. In a study applying this method to Manitoba grain farms, it was found that adjustments in the organization and intensity of farming offset the effects of distance on net income.     

Coastal erosion and the cape hatteras lighthouse

The famous Cape Hatteras Lighthouse is threatened with destruction by an eroding coastline. Recent attempts to control the erosion have reduced but not stopped it The natural erosion trend for 41 km of coast from Rodanthe to Cape Hatteras was determined, based on 94 years of survey records from 1852 to 1946 At the lighthouse, the natural erosion rate is 7 5 m/yr In 2005, if no further human interference with coastal processes occurs, 190 m of coast will have eroded since 1980, leaving the shoreline nearly 90 m west of the lighthouse Considering the expensive effort being undertaken to protect the lighthouse from destruction, an inventory of property along the Atlantic coast should be made, before other similar projects are initiated We can afford to protect only the most valuable property.     

Strain analysis using deformed pebbles: The influence of initial pebble shape

Several methods exist for the determination of the finite strain ellipsoid from deformed pebble shapes. These methods are critically evaluated and others are proposed on the basis of calculations which predict both the sectional and three-dimensional shape of pebbles in simple deformed simulated conglomerates. In many cases it is found preferable to use an average pebble shape to estimate the tectonic strain and that the harmonic mean of the ratios of axial lengths yields an average pebble shape which is closest to the strain ellipsoid shape.     

The Lamprey River Hydrological Observatory: Suburbanization and changing seasonality

The Lamprey River Hydrological Observatory (LRHO) is a lowland coastal watershed in southeastern New Hampshire (USA). The LRHO offers a platform to investigate the effects of suburbanization and changing seasonality on watershed hydrology, biogeochemistry, and nutrient export to an estuarine ecosystem. The LRHO utilizes a nested-watershed design to examine headwater stream and main-stem river dynamics distributed across a mixed land-use environment. Data sets from the LRHO now comprise over 20 years of weekly grab sample data as well as 7 years of high-frequency sensor data. Collectively these data sets include measures of discharge, dissolved organic matter, nutrients, cations and anions, greenhouse gases, and other physio-chemical properties. Here we share information on the setting and motivating questions of the LRHO and data availability.     

Formation of stationary alternate bars in a steep channel with mixed-size sediment: A flume experiment

Alternate bars were formed by sediment transport in a flume with Froude-modelled flow and relative roughness characteristic of gravel-boulder channels with steep slopes. The flume (0.3 m wide × 7.5 m long) was filled with a sand-gravel mixture, which was also fed into the top of the flume at a constant rate under constant discharge. Channel slope was set at 0.03. Initially, coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream. Sorting in the pool directed coarse particles onto the next bar head downstream. Alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting, flow, and channel morphology. During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited. Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar-head erosion and bedload transport over bars. Likely factors leading to bar-head stabilization in modelled gravel-bed channels are coarse mixed-size sediment, steep channel gradients, and shallow depths.