Letters from Carlos Ibáñez e Ibáñez de Ibero to Aimé Laussedat: new sources for the history of nineteenth century geodesy

Recently found letters written by Carlos Ibáñez e Ibáñez de Ibero (1825–1891), first president of the International Geodetic Association, to geodesist–photogrammetrist Aimé Laussedat (1819–1907) are discussed. The contents of these epistolary conversations reflect their personal preoccupation with solving the geodetic problems of the time (1857–1889) and their desire to develop and propagate geodetic knowledge across all international boundaries.     

Storm-water hydrograph separation of run off from a mine-tailings impoundment formed by thickened tailings discharge at Kidd Creek, Timmins, Ontario

The Kidd Creek Cu---Zn sulphide mine is located near Timmins, Ontario. Mill tailings are thickened and deposited as a thickened slurry in a circular, conical-shaped pile with an area of approximately 1200 ha. Deposition of tailings as a thickened slurry results in a relatively uniform grain-size distribution and hydraulic conductivity, and a thick tension-saturated zone above the water table. The tailings are drained by numerous small, ephemeral stream channels, which have developed in a radial pattern. During storms, water from these streams collects in catchment ponds where it is held before treatment. The contribution of tailings pore water to the run off is of interest because of the potential for discharge of pore water containing high concentrations of Fe(II)-acidity, metals and SO₄ to the stream. Hydraulic head measurements, measurements of water-table elevation and groundwater flow modelling were conducted to determine the mechanisms responsible for tailings pore water entering the surface streams. Chemical hydrograph separation of storm run off in one of these streams, during three rainfall events, using Na and Cl as conservative tracers, indicates that the integrated tailings pore water fraction makes up between less than 1 % and 20% of the total hydrograph. This range is less than the maximum fraction of tailings pore water of 22–65% reported for run off from a conventional tailings deposit. At this site, preferential flow through permeable fractures may be the dominant mechanism causing discharge of tailings pore water to storm run off. Estimates of the mass of Fe(II) that discharges to the surface run off from the pore water range up to 2800 mg s⁻¹ during a moderate intensity, long duration rainfall event. The greatest potential for discharge of significant masses of solutes derived from the pore water exists during long duration rainfall events, when the water table rises to the surface over large areas of the tailings impoundment.     

Contact conditions on seismoactive faults

Square plate models with a diagonally located slit in compression were studied photoelastically. The resulting stress field surrounding the discontinuity (slit) is evaluated before and after seismoactive (seismic-energy-releasing) shear displacement. The mechanism of the fast shear movement (stick-slip), including its radiation properties, in interpreted. The results confirm the existence of a central locked zone in the loaded slit, the limits of which coincide with the initiation points of stick-slip movements. The zone is interpreted as the source of the seismic energy release. The complementary measurements (direct optical and ultrasonic) are presented to verify the results of the photoelastic analysis. The results obtained are discussed in regard to the conclusions that follow from the theory of elasticity.     

Star formation in taurus

Data with the 2MASS prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from IRAS observations to contain a number of very young solar type stars. Data at 1.25 (J), 1.65 (H), and 2.2 (K _s )µm are presented. These data are representative of the type and quality of data expected from the planned near-IR surveys, 2MASS and DENIS. Near-IR surveys will be useful for determining the large scale variation of extinction with clouds, for determining the luminosity function in nearby clouds down to ranges of 0.1–1.0 L, and for finding highly extincted T Tauri stars missed by IRAS because the bulk of their luminosity is emitted shortward of 12µm.     

Late Paleozoic orogeny in Alaska's Farewell terrane

Evidence is presented for a previously unrecognized late Paleozoic orogeny in two parts of Alaska's Farewell terrane, an event that has not entered into published scenarios for the assembly of Alaska. The Farewell terrane was long regarded as a piece of the early Paleozoic passive margin of western Canada, but is now thought, instead, to have lain between the Siberian and Laurentian (North American) cratons during the early Paleozoic. Evidence for a late Paleozoic orogeny comes from two belts located 100–200 km apart. In the northern belt, metamorphic rocks dated at 284–285 Ma (three ⁴⁰Ar/³⁹Ar white-mica plateau ages) provide the main evidence for orogeny. The metamorphic rocks are interpreted as part of the hinterland of a late Paleozoic mountain belt, which we name the Browns Fork orogen. In the southern belt, thick accumulations of Pennsylvanian-Permian conglomerate and sandstone provide the main evidence for orogeny. These strata are interpreted as the eroded and deformed remnants of a late Paleozoic foreland basin, which we name the Dall Basin. We suggest that the Browns Fork orogen and Dall Basin comprise a matched pair formed during collision between the Farewell terrane and rocks to the west. The colliding object is largely buried beneath Late Cretaceous flysch to the west of the Farewell terrane, but may have included parts of the so-called Innoko terrane. The late Paleozoic convergent plate boundary represented by the Browns Fork orogen likely connected with other zones of plate convergence now located in Russia, elsewhere in Alaska, and in western Canada.