Postshield stage transitional volcanism on Mahukona Volcano, Hawaii     

David A. Clague  Andrew T. Calvert 《Bulletin of Volcanology》2009,71(5):533-539

Age spectra from ⁴⁰Ar/³⁹Ar incremental heating experiments yield ages of 298 ± 25 ka and 310 ± 31 ka for transitional composition lavas from two cones on submarine Mahukona Volcano, Hawaii. These ages are younger than the inferred end of the tholeiitic shield stage and indicate that the volcano had entered the postshield alkalic stage before going extinct. Previously reported elevated helium isotopic ratios of lavas from one of these cones were incorrectly interpreted to indicate eruption during a preshield alkalic stage. Consequently, high helium isotopic ratios are a poor indicator of eruptive stage, as they occur in preshield, shield, and postshield stage lavas. Loihi Seamount and Kilauea are the only known Hawaiian volcanoes where the volume of preshield alkalic stage lavas can be estimated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Observations of the supernova SN1987L with the new Faint Object Spectrograph on the 4.2 m William Herschel Telescope     

Gillian Pearce  Bruce Patchett  Jeremy Allington-Smith  Ian Parry 《Astrophysics and Space Science》1988,150(2):267-271

We present the spectrum of the supernova SN1987L in NGC 2336 over the wavelength range 4000–9700 Å as recorded in one 500 s exposure on 20–21 October, 1987. This spectrum was taken using the new Faint Object Spectrograph on the 4.2 m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos.We conclude that SN1987L was a type Ia supernova, and approximately 100 days post maximum at the time of the observation.  相似文献   

Timing and cause of water level fluctuations in Kluane Lake, Yukon Territory, over the past 5000 years     

Janice Brahney  John J. Clague  Thomas 《Quaternary Research》2008,70(2):213-227

We reconstructed late Holocene fluctuations of Kluane Lake in Yukon Territory from variations in bulk physical properties and carbon and nitrogen elemental and isotopic abundances in nine sediment cores. Fluctuations of Kluane Lake in the past were controlled by changes in climate and glaciers, which affected inflow of Slims and Duke rivers, the two largest sources of water flowing into the lake. Kluane Lake fluctuated within a narrow range, at levels about 25 m below the present datum, from about 5000 to 1300 cal yr BP. Low lake levels during this interval are probably due to southerly drainage of Kluane Lake to the Pacific Ocean, opposite the present northerly drainage to Bering Sea. Slims River, which today is the largest contributor of water to Kluane Lake, only rarely flowed into the lake during the period 5000 to 1300 cal yr BP. The lake rose 7-12 m between 1300 and 900 cal yr BP, reached its present level around AD 1650, and within a few decades had risen an additional 12 m. Shortly thereafter, the lake established a northern outlet and fell to near its present level.  相似文献   

Natural hazards,extreme events,and mountain topography     

Oliver Korup  John J. Clague 《Quaternary Science Reviews》2009,28(11-12):977-990

The hazard of any natural process can be expressed as a function of its magnitude and the annual probability of its occurrence in a particular region. Here we expand on the hypothesis that natural hazards have size–frequency relationships that in parts resemble inverse power laws. We illustrate that these trends apply to extremely large events, such as mega-landslides, huge volcanic debris avalanches, and outburst flows from failures of natural dams. We review quantitative evidence that supports the important contribution of extreme events to landscape development in mountains throughout the world, and propose that their common underreporting in the Quaternary record may lead to substantial underestimates of mean process rates. We find that magnitude–frequency relationships provide a link between Quaternary science and natural hazard research, with a degree of synergism and societal importance that neither discipline alone can deliver. Quaternary geomorphology, stratigraphy, and geochronology allow the reconstruction of times, magnitudes, and frequencies of extreme events, whereas natural hazard research raises public awareness of the importance of reconstructing events that have not happened historically, but have the potential to cause extreme destruction and loss of life in the future.  相似文献   

Time-series analysis of six whale-fall communities in Monterey Canyon,California, USA     

Lonny Lundsten  Kyra L. Schlining  Kaitlin Frasier  Shannon B. Johnson  Linda A. Kuhnz  Julio B.J. Harvey  Gillian Clague  Robert C. Vrijenhoek 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(12):1573-1584

Dead whale carcasses that sink to the deep seafloor introduce a massive pulse of energy capable of hosting dynamic communities of organisms in an otherwise food-limited environment. Through long-term observations of one natural and five implanted whale carcasses in Monterey Canyon, CA, this study suggests that: (1) depth and related physical conditions play a crucial role in species composition; (2) the majority of species in these communities are background deep-sea taxa; and (3) carcass degradation occurs sub-decadally. Remotely operated vehicles (ROVs) equipped with studio quality video cameras were used to survey whales during 0.8 to seven year periods, depending on the carcass. All organisms were identified to the lowest possible taxon. Community differences among whale-falls seemed to be most strongly related to depth and water temperature. The communities changed significantly from initial establishment shortly after a carcass’ arrival at the seafloor through multiple years of steady degradation. The majority of species found at the whale-falls were background taxa commonly seen in Monterey Bay. While populations of species characterized as bone specialists, seep restricted, and of unknown habitat affinities were also observed, sometimes in great abundance, they contributed minimally to overall species richness. All whale carcasses, shallow and deep, exhibited sub-decadal degradation and a time-series of mosaic images at the deepest whale site illustrates the rapidity at which the carcasses degrade.  相似文献   

Holocene paleohydrology of a hypersaline lake in southeastern Alberta     

R. E. Vance  J. J. Clague  R. W. Mathewes 《Journal of Paleolimnology》1993,8(2):103-120

Analyses of pollen, plant macrofossils, sediment mineralogy, geochemistry, and lithology of cores from Chappice Lake, southeastern Alberta, provide an outline of paleohydrological changes spanning the last 7300 radiocarbon years. Situated near the northern margin of the Great Plains, Chappice Lake is currently a small (1.5 km²), shallow (<1 m), hypersaline lake. Results of this study suggest that the lake has experienced significant changes in water level and chemistry during the Holocene.From 7300 to 6000 BP the lake oscillated between relatively high stands and desiccation. From 6000 to 4400 BP it was smaller than present and ponded highly saline water. Although extreme water level variations of the preceding period had ceased, pronounced seasonal fluctuations persisted. Between 4400 and 2600 BP, lake level was more stable but gradually rising. Carbonates were a major component of the sediments deposited during this interval. A large, relatively fresh lake existed from 2600 to 1000 BP. Illite was the dominant mineral deposited during this period, but since then has been a minor constituent in a mineral suite dominated by detrital silicates. A series of low-water, high-salinity stands occurred between 1000 and 600 BP, although these low stands were not as pronounced as low-water intervals in the middle Holocene. Relatively high water levels were sustained from 600 BP until the late 1800s. The lake declined significantly in the last one hundred years, notably during the historically documented droughts of the late 1800s, 1920s, 1930s, and 1980s.The timing of paleohydrological events at Chappice Lake corresponds closely with well documented Holocene climatic intervals, such as the Hypsithermal, Neoglaciation, Medieval Warm Period, and Little Ice Age. In addition, historic lake-level fluctuations can be related directly to climate. As a result, the Chappice Lake sedimentary succession offers a rare opportunity to obtain a high-resolution, surrogate record of Holocene climate on the northern Great Plains, and to observe the response of lake chemistry and biota to significant environmental change.Geological Survey of Canada Contribution No. 45191, Palliser Triangle Global Change Contribution No. 2This publication is the first of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor for this series.  相似文献   

Early growth of the last Cordilleran ice sheet deduced from glacio-isostatic depression in southwest British Columbia, Canada     

John J. Clague  Duane Froese  Ian Hutchinson  Karen M. Simon 《Quaternary Research》2005,63(1):53-59

Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation.  相似文献   

Volcaniclastic deposits from the North Arch volcanic field, Hawaii: explosive fragmentation of alkalic lava at abyssal depths     

Alicé S. Davis  David A. Clague 《Bulletin of Volcanology》2006,68(3):294-307

Submarine explosive eruptions are generally considered to become less likely with increasing depth due to the increasing hydrostatic pressure of the overlying water column. Volcaniclastic deposits from the North Arch volcanic field, north of Oahu, have textural characteristics of explosive fragmentation yet were erupted in water depths greater than 4,200 m. The most abundant volcaniclastic samples from North Arch are clast-supported with highly vesicular, angular pyroclasts. They are most likely near-vent pyroclastic fall deposits formed in eruption columns of limited height. Interbedded with highly vesicular pillow lava, they form low (50 to 200 m), steep-sided cones around the vents. Less common are stratified samples with graded bedding; one such sample includes a layer of roughly aligned, platy, bubble-wall glass fragments (resembling littoral limu o Pele) that may have been deposited by density currents. In addition to bubble-wall glass shards, numerous glass fragments with spherical, delicate spindle and ribbon shapes, and Pele's hair-like glass strands occur in the finer size fraction (<0.5 mm) of some samples. They are probably more distal fallout. Another sample, consisting of glass fragments dispersed in a marine clay matrix, was apparently reworked and deposited farther from the vents by bottom currents. Glass compositions include low-(∼0.4-0.6 wt%) and medium-K₂O (>0.6 wt%) alkalic basalt, basanite, and nephelinite. Sulfur and chlorine abundances are high, reaching a maximum of 1,800 and 1,300 ppm, respectively. The ubiquitous presence of limu o Pele fragments, regardless of glass composition, suggests that bursts of Strombolian-like activity accompanied most eruptions. Coalescing vesicles observed in larger pyroclasts and some pillow lava suggests accumulation of volatiles. Since the great hydrostatic pressure makes steam expansion impossible, a volatile-rich, supercritical magmatic fluid probably drove the eruptions. If these volatile-rich magmas had erupted in shallow water or subaerially, tall fountains would most likely have resulted. The great hydrostatic pressure (>40 MPa) limited fountain and eruption column heights.  相似文献   

1,000-year record of landslide dams at Halden Creek, northeastern British Columbia     

Marten Geertsema  John J. Clague 《Landslides》2006,3(3):217-227

Large, rapid, low-gradient landslides are common in clay-rich glacial sediments in northeastern British Columbia. Many of the landslides create upstream impoundments that may persist for years in small watersheds in the region. We have documented such events in the Halden Creek watershed, 60 km southeast of Fort Nelson. The events are recorded geologically in two ways. First, trees are drowned in lakes dammed by the landslides and subsequently buried by deltaic sediments, where they are protected from decay. Bank erosion later exhumes the drowned trees. Second, landslide deposits with entrained wood are exposed along stream banks. We have reconstructed the recent history of landslide damming at Halden Creek by performing radiocarbon dating on exhumed trees and wood in and beneath landslide deposits at 13 sites in the watershed. Drowned trees range in age from 169±59 to 274±49 ¹⁴C year bp. Wood in and below landslide deposits yielded radiocarbon ages ranging from modern to 965±49 ¹⁴C year bp.  相似文献   

Reversals of the Earth's Magnetic Field     

J.A. Jacobs  Gillian M. Turner 《Geophysical Journal International》1995,121(3):975-975

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