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Research about British Columbia

Source-linked reports with geographic coverage including British Columbia.

44 records · Page 3Linked to original sources
USGS1999

Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

This report describes the acquisition and processing of deep-crustal wide-angle seismic reflection and refraction data obtained in the vicinity of Puget Lowland, the Strait of Juan de Fuca, and Georgia Strait, western Washington and southwestern British Columbia, in March 1998 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As part of a larger initiative to better understand lateral variations in crustal structure along the Cascadia margin, SHIPS participants acquired 1000 km of deep-crustal multichannel seismic-reflection profiles and 1300 km of wideangle airgun shot lines in this region using the R/V Thompson and R/V Tully. The Tully was used to record airgun shots fired by the Thompson in two different geometries: (1) expanding spread profiles (ESPs) and (2) constant offset profiles (COPs). Prior to this reflection survey, we deployed 257 Reftek and 15 ocean-bottom seismic recorders to record the airgun signals at far offsets. All data were recorded digitally on large-capacity hard disks. Although most of these stations only recorded the vertical component of motion, 95 of these seismographs recorded signals from an oriented 3-component seismometer. By recording signals generated by the Thompson's marine air gun array, operated in two differing geometries having a total volume of 110 and 79 liters (6730 and 4838 cu. in.), respectively, the arrays of wide-angle recorders were designed to (1) image the crustal structure, particularly in the vicinity of crustal faults and Cenozoic sedimentary basins, (2) determine the geometry of the Moho, and (3) image the subducting Gorda and Juan de Fuca plates. Nearly 33,300 air gun shots were recorded along several seismic lines. In this report, we illustrate the expanding spread profiles acquired using the Thompson and Tully, describe the land and ocean-bottom recording of the air gun signals, discuss the processing of the land recorder data into common receiver gathers, and illustrate the processed wide-angle seismic data collected using the Refteks and ocean-bottom seismometers. We also describe the format and content of the archival tapes containing the SEGY-formated, common-receiver gathers for the Reftek data. Data quality is variable but SHIPS appears to have successfully obtained useful data from almost all the stations deployed to record the airgun shots. Several interesting arrivals were observed: including refractions from the sedimentary basin fill in several basins, refractions from basement rocks forming the upper crust, Pg, refractions from the upper mantle, Pn, as well as reflections from within the crust and from the top of the upper mantle, PmP. We separately archived more than 30 local earthquakes recorded by the Reftek array during our deployment.

Washington↗
USGS1995

Intraglacial volcanism in the Wells Gray–Clearwater volcanic field, east-central British Columbia, Canada

Small-volume, subaerial, subaqueous and subglacial basaltic eruptions occurred in the Wells Gray–Clearwater area during Quaternary time. Part of this time, significant thicknesses of glacial ice were present. Dating of intraglacial volcanic features corroborates other evidence of an Early Pleistocene, Cordilleran-wide ice sheet. Of the intraglacial volcanoes investigated, three were studied in detail and of these, two probably erupted during the Fraser glaciation (11–20 ka), when maximum ice level exceeded 2100 m elevation. Major-element and sulphur concentrations were measured in glass from the volcanoes to provide insight into vent conditions at the time of eruption. Hyalo Ridge (2102 m elevation, whole-rock K–Ar age of 0.02 ± 0.01 Ma) is a small volcanic edifice capped by lava flows with coherent pillowed lavas and interbedded hyaloclastite exposed over nearly 400 m altitude on its east flank. Low sulphur content (<0.03 wt.%) in pillow rim glasses indicates that the lavas are degassed. It is interpreted that the vent built above the water (or ice) surface then fed lava flows that crossed a shoreline and produced pillowed flows. Pyramid Mountain is a volcanic cone 240 m high, comprised of glassy, vesicular, lapilli-tuff breccia. The highly alkalic glass contains 0.1 wt.% S (considered high), and indicates a high original volatile content and drastic quenching, probably during phreatomagmatic eruption from a meltwater-flooded vent. East of the Clearwater River a sequence of massive pillowed flows and pillow joint-block breccias is exposed from 880 to 1320 m elevation (0.27 ± 0.05 Ma). The vent location is unknown. Moderate S content (0.040–0.055 wt.%) indicates that the lavas were erupted in shallow water and are largely degassed. The S content of glass in dykes cutting the pillow breccias is low. The dykes are interpreted as lava that has flowed laterally or down into cracks

British Columbia↗
USGS1991

Radiocarbon test of earthquake magnitude at the Cascadia subduction zone

The Cascadia subduction zone, which extends along the northern Pacific coast of North America, might produce earthquakes of magnitude 8 or 9 ('great' earthquakes) even though it has not done so during the past 200 years of European observation 1–7 . Much of the evidence for past Cascadia earthquakes comes from former meadows and forests that became tidal mudflats owing to abrupt tectonic subsidence in the past 5,000 years 2,3,6,7 . If due to a great earthquake, such subsidence should have extended along more than 100 km of the coast 2 . Here we investigate the extent of coastal subsidence that might have been caused by a single earthquake, through high-precision radiocarbon dating of coastal trees that abruptly subsided into the intertidal zone. The ages leave the great-earthquake hypothesis intact by limiting to a few decades the discordance, if any, in the most recent subsidence of two areas 55 km apart along the Washington coast. This subsidence probably occurred about 300 years ago.

California, Oregon, Washington↗
USGS1991

Late Cretaceous and early Tertiary plutonism and deformation in the Skagit Gneiss Complex, north Cascade Range, Washington and British Columbia

The Skagit Gneiss Complex forms a more-or-less continuous terrane within the northern, more deeply eroded part of the North Cascade Range. The complex comprises abundant plutons intruded at mid-crustal depths into a variety of metamorphosed supracrustal rocks of both oceanic and volcanic-arc origin. A plethora of syntectonic pegmatite, small plutons, and granitic dikes gives the complex a migmatitic aspect. U-Pb zircon ages from gneissic plutons within and near the Skagit Gneiss Complex indicate magmatic crystallization between 75 and 60 Ma. Deformation, recrystallization, and migmatization in part postdate intrusion of the 75-60 Ma plutons. This latest Cretaceous and earliest Tertiary plutonism and migmatization may reflect thermal relaxation following early Late Cretaceous orogeny documented else-where in the North Cascades. The complex was ductilely extended northwest-southeast shortly after intrusion of granite dikes at ∼45 Ma, but before emplacement of the earliest (∼34 Ma) plutons of the Cascade arc. Outcrops of Late Cretaceous and earliest Tertiary plutons, migmatites of the Skagit Gneiss Complex, and rocks with young ductile deformation are roughly coextensive, all apparently marking a region of greater middle Eocene unroofing. Unroofing was apparently contemporaneous with east-west extension in the Okanogan region to the east and north-south and northwest-southeast strike-slip faulting within the North Cascades.

Washington↗
USGS1984

Neogene molluscan stages of the West Coast of North America

Neogene marine sediments of the West Coast of North America were deposited in a series of widely spaced basins that extended geographically from the western and northern Gulf of Alaska (60°N) to southern California (33°N). Rich molluscan faunas occur extensively throughout these deposits and form the basis for biostratigraphic schemes that are useful for correlating within and between individual basins. Early biostratigraphic work was concerned with faunas from particular horizons and with the stratigraphic range of diverse taxa, such as Pecten and Turritella , without reference to other fossil groups. Succeeding work increasingly dealt with the relationships of molluscan zones to benthic and, later, planktonic foraminiferal stages. In recent years the age limits of Neogene molluscan stages have become better documented by reference to planktonic microfossils from dated DSDP cores and onshore faunas. Neogene molluscan faunas from California, the Pacific Northwest states (Oregon and Washington), and southern Alaska have been treated separately due to differences in faunal composition and geographic isolation. As a result, a different biostratigraphic sequence has been described for each region. Pacific Northwest stages have been formally named and defined, and their names are also used informally for Alaskan faunas. California Neogene stages were proposed early in this century, are in need of redescription, and their usage is informal. Precise correlations between the three regional sequences have not yet been achieved, due to the low number of co-occurring species and the general lack of planktonic microfossils in these largely shallow-water faunas. The objectives of ongoing research include: fuller documentation of the faunas of California and Pacific Northwest stages; formal description of California stages; improved correlation between regional stage sequences; refinement of age estimates for stage boundaries; and, establishment of Neogene stages for Alaskan faunas.

California, Oregon, Washington↗
USGS1978

Simulation model of Cryptomonas ovata population dynamics in southern Kootenay Lake, British Columbia

A one-dimensional transient model is developed to simulate observed population dynamics of a small flagellate ( Cryptomonas ovata ) in southern Kootenay Lake, B.C., during a 1-year period (1 June 1974-31 May 1975). The model considers advective displacement of C. ovata as water flows from its southern entrance into the lake and moves northward toward sampling sites. Specific growth rate is computed from an experimentally determined function of mean irradiance, water temperature, and nutrient (ammonium and phosphate) concentration in the upper 10 m of the water column. Cell losses are assumed to result from zooplankton grazing and inhibition due to presence of the blue-green alga Anabaena . The model simulates well the timing and magnitude of all observed population changes and, more importantly, it gives insight into the important mechanisms which regulate population density of C. ovata in this natural system.

British Columbia↗
USGS1976

Recent limnological changes in southern Kootenay Lake, British Columbia

n response to a significant abatement of phosphate loading and the construction of a dam on its major inflow (the Kootenay River), southern Kootenay Lake experienced a number of limnological changes between 1969 and 1974. Water temperatures in 1974&ndash;1975 were similar to those previously reported for 1966&ndash;1969. However, water transparency has increased, particularly during the spring months.Nitrate concentrations have remained unchanged since 1969, and ranged from 2 to 8&ensp;&mu; M between 6 June 1974 and 22 May 1975. However, ammonium levels have been reduced in the winter months when mean concentration was about 1&ensp;&mu; M . Dissolved phosphorus levels in 1966&ndash;1969 were consistently around 3&ensp;&mu; M , but never reached 1&ensp;&mu; M in 1974. Phytoplankton populations in 1974&ndash;1975 (measured as chlorophyll a ) were lower than those during the 1966&ndash;1969 period, and evidence is presented that suggests that major shifts have occurred in the species composition of the phytoplankton. Whereas Kootenay Lake experienced blue&ndash;green and green algal blooms during the 1960's, no such phenomena were observed in 1974&ndash;1975 when the plankton was dominated by diatoms. Population maxima of the three most common zooplankters ( Cyclops bicuspidatus , Diaptomus ashlandi , and Diaphanosoma leuchtenbergianum ) have increased since 1966&ndash;1969.

British Columbia↗