A new 40Ar/39Ar eruption age for the Mount Widderin volcano,Newer Volcanic Province,Australia, with implications for eruption frequency in the region     

E. L. Matchan  E. B. Joyce  D. Phillips 《Australian Journal of Earth Sciences》2016,63(2):175-186

The Mount Widderin shield volcano is located near Skipton, western Victoria, in the Western Plains subprovince of the monogenetic Pliocene–Holocene Newer Volcanic Province (NVP). Radiometric ages for lavas in the Hamilton–Skipton–Derrinallum area are few, owing to limited suitable outcrop for K–Ar or ⁴⁰Ar/³⁹Ar geochronology studies. Existing age constraints for flows in this area have been inferred from Regolith Landform Units (RLUs), complemented by a small number of K–Ar studies on ≥1 Ma flows. Although the RLU approach provides a valuable overview of relative eruption ages across the NVP, it is of limited use in eruption frequency studies. Additional radio-isotopic ages are required to refine age ranges for individual RLUs, and to validate previous assignment of individual flows to specific RLUs. We report a new, high-precision ⁴⁰Ar/³⁹Ar age of 389 ± 8 ka (2σ) for a Mount Widderin basalt sample. Based on this age and geomorphic observations, we propose that both the Widderin and Elephant lava flows be reassigned from the Eccles RLU to the Rouse RLU. We use the 389 ± 8 ka (2σ) age for Widderin, along with published K–Ar ages, to anchor a stratigraphic sequence of 15 individual flows in the Hamilton–Skipton–Derrinallum area, demonstrating that intermittent volcanism has occurred in this area from ≥3 Ma to ≤0.389 Ma. Within the limits of available data for the NVP, this time span of volcanic activity is second only to that of the Melbourne area. We consider the significance of the Widderin eruption age, in conjunction with published age constraints for maars and scoria cones of the Western Plains subprovince, building on previous studies that have focused solely on lava flow ages. The inclusion of the additional data weakens the argument for a decrease in volcanic activity after ca 0.9 Ma as implied by published ages for lava flows only. Additional detailed combined geochronology–geomorphology studies of lavas, scoria cones and maars in strategically selected small areas are advocated to better understand eruption frequency across the NVP.  相似文献   

Practices in disaster mitigation in the case of the 2015 Typhoon Koppu debris flows in Nueva Ecija,Philippines     

Llanes  Francesca V.  Eco  Rodrigo  Herrero  Tatum Miko  Briones  Jo Brianne Louise  Escape  Carmille Marie  Sulapas  Jolly Joyce  Galang  Jan Albert Macario  Ortiz  Iris Jill  Sabado  Jasmine May  Lagmay  Alfredo Mahar Francisco  Rodolfo  Kelvin 《Natural Hazards》2022,114(1):665-690

Natural Hazards - In October 2015, heavy rains brought by Typhoon Koppu generated landslides and debris flows in the municipalities of Bongabon, Laur, and Gabaldon in Nueva Ecija province....  相似文献   

The evolution of Rapid Burster outbursts     

R. Guerriero    D. W. Fox    J. Kommers    W. H. G. Lewin    R. Rutledge    C. B. Moore    E. Morgan    J. Van Paradijs    M. Van der Klis    L. Bildsten  T. Dotani 《Monthly notices of the Royal Astronomical Society》1999,307(1):179-189

We describe the evolutionary progression of an outburst of the Rapid Burster. Four outbursts have been observed with the Rossi X-Ray Timing Explorer between 1996 February and 1998 May, and our observations are consistent with a standard evolution over the course of each. An outburst can be divided into two distinct phases. Phase I is dominated by type I bursts, with a strong persistent emission component; it lasts for 15–20 d. Phase II is characterized by type II bursts, which occur in a variety of patterns. The light curves of time-averaged luminosity for the outbursts show some evidence for reflares, similar to those seen in soft X-ray transients. The average recurrence time for Rapid Burster outbursts during this period was 218 d, in contrast to an average ∼180‐d recurrence period observed during 1976–1983.  相似文献   

A new statistic for picking out non-Gaussianity in the CMB     

Alex Lewin  reas Albrecht  João Magueijo 《Monthly notices of the Royal Astronomical Society》1999,302(1):131-138

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Cooling of the quasi-persistent neutron star X-ray transients KS 1731−260 and MXB 1659−29     

Edward M. Cackett  Rudy Wijnands  Manuel Linares  Jon M. Miller  Jeroen Homan  Walter H. G. Lewin 《Monthly notices of the Royal Astronomical Society》2006,372(1):479-488

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Persistent blooms of surf diatoms along the pacific coast,U.S.A.: I. Physical characteristics of the coastal region in relation to the distribution and abundance of the species     

Janice Lee Garver  Joyce Lewin 《Estuarine, Coastal and Shelf Science》1981,12(2):217-229

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Comparison of the Climate during Marine Isotope Stage 9 and 11 Inferred from a Speleothem Isotope Record from Northern Norway     

Ida M. Berstad  Joyce Lundberg  Stein-Erik Lauritzen  Henriette C. Linge 《Quaternary Research》2002,58(3):361

A stalagmite from northern Norway is dated with 12 thermal ionization mass spectrometry U-Th dates, and at least four separate growth periods are identified that correspond with marine isotope stages 9, 11, 13, and probably 15. The calcite is tested for isotopic equilibrium with the Hendy test. Oxygen isotope measurements on 231 subsamples on a vertical transect are used as a paleotemperature proxy. The detailed isotopic record from MIS 9 show apparent similarities to a Holocene record from the same cave, both in the climatic evolution and the overall temperatures: both show temperature oscillations changing from high-frequency, low-amplitude cycles in the beginning of the interglacial period to lower frequency, higher amplitude cycles in the later part of the interglacial period. The isotope record from MIS 11 shows a distinct isotopic event toward heavier values. The isotopic record together with the porous, humus-rich calcite are interpreted as indicating a warmer than present interglacial period with several episodes of heavy rainfall.  相似文献   

Copper bioavailability to marine bivalves and shrimp: Relationship to cupric ion activity     

E.A Crecelius  J.T Hardy  C.I Gibson  R.L Schmidt  C.W Apts  J.M Gurtisen  S.P Joyce 《Marine environmental research》1982,6(1):13-26

Studies were performed to determine the effects of dissolved substances present in natural seawater and sediment on the bioavailability of added Cu⁺². Whole clams Macoma inquinata and shrimp, Pandalus danae, were exposed to four concentrations of Cu in a flow-through seawater system. Bioaccumulation of Cu was reduced in shrimp, Pandalus danae, clams, M. inquinata, and excised clam gills, Protothaca staminea, exposed to an aged, compared with an unaged, Cu-seawater solution. This is thought to be due to slow complexation of the Cu by dissolved substances present in natural seawater. In a static system, with added sediment, more than 50% of the added Cu⁺² became bound to the organic fraction of the sediment and was unavailable to suspension feeding clams, Protothaca staminea. In contrast, deposit feeding clams, Macoma inquinata, placed in the sediment approximately doubled in Cu body burden within two months.Complexed Cu appears to be less bioavailable than ionic Cu and hence measurements of ionic and weakly complexed Cu by differential pulse anodic stripping voltametry provide a better prediction of bioavailable Cu than conventional measurements of total Cu-seawater concentrations.  相似文献   

Temporal variation in the structure of autotrophic and heterotrophic communities in the subarctic Pacific     

Beatrice C. Booth  Joyce Lewin  James R. Postel 《Progress in Oceanography》1993,32(1-4)

Autotrophic and microheterotrophic plankton populations were monitored in the euphotic zone of the eastern subarctic Pacific during 6 one-month cruises in spring and summer, 1984, 1987 and 1988. Transmitted light, epifluorescence, and electron microscopy were used to identify, enumerate and estimate the biomass of size-populations of species. The 2–10μm size class dominated the biomass of both autotrophs and heterotrophs. The autotrophic flagellate, Phaeocystis pouchetii, was frequently observed in its non-colonial phase. Temporal variation in all the stocks was evident and could be explained only partially by the physical, chemical or biological factors investigated here. The general structure of the autotrophic community was similar to that in the North Atlantic, but major, unexplained variations between cruises occurred. Variation in mixed-layer depth and day length (but not variation in daily insolation) explained 25% of the variation in autotrophic doubling rate. Heterotrophic biomass comprised, in decreasing order of importance, non-pigmented flagellates, dinoflagellates, and ciliates. Ciliates rarely contributed more than 40% to the total. Microheterotrophic biomass rarely exceeded 30μg C 1⁻¹ (avg 15μg C 1⁻¹, 0–60m) whereas autotrophic biomass averaged 20μg C 1⁻¹, 0–60m, and reached 74μg C 1⁻¹ on one occasion, yet the grazing capacity of these microheterotrophs averaged 100% of primary production.  相似文献   

Cracking up: faulting on Earth and Mars     

Joyce Vetterlein  Gerald P Roberts 《Astronomy& Geophysics》2003,44(4):4.22-4.22

Joyce Vetterlein and Gerald P Roberts describe research in progress on the structural evolution of Cerberus Fossae, Mars, with implications for cryosphere cracking in recent Mars history.  相似文献