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1.
To determine periods of incremental landslide movement and their possible relationship to regional seismic events, the tree-ring records of 32 tilted and damaged conifers at three sites on landslides in the Gravelly Range of southwestern Montana were examined. Several signs of disturbance in the tree-ring record indicating landslide movement were observed. Commonly, the tree-ring record displayed a marked reduction in annual ring width and/or the reaction wood formation. The tree-ring records from the three landslide sites indicate multiple periods of movement during the 20th century. Many of the periods of movement indicated by the strongest signals (most trees) at the sites occurred the year following significant earthquakes in the region. Those seismic events for which evidence in the tree-ring record was found at one or more of the three sites are the 1983 Borah Peak, 1959 Hebgen Lake, 1935 Helena, 1925 Clarkson, and 1908 Virginia City earthquakes. This study suggests that many of the landslide movements were triggered by, or are coincident with, earthquakes as much as 200 km from the study area. 相似文献
2.
Toshifumi Yanagisawa Yasushi Muraki Yutaka Matsubara Fumio Abe Kimiaki Masuda Sachiyo Noda Takahiro Sumi Yuji Kato Mitsuaki Fujimoto Shuji Sato Ian Bond Nicholas Rattenbury Philip Yock Pam Kilmartin John Hearnshaw Micheal Reid Denis Sullivan Brian Carter Richard Dodd Garry Nankivell Noiman Rumsey Morihiro Honda Maki Sekiguchi Masanori Yoshizawa Takashi Nakamura Humitaka Sato Seiji Kabe Makoto Kobayashi Yoshiyuki Watase Jun Jugaku Toshiharu Saito Barbel Koribalsky 《Experimental Astronomy》2000,10(4):519-535
We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration. 相似文献
3.
4.
Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States 总被引：2，自引：0，他引：2
Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United
States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin
and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites
are generally calc-alkaline, magnesian, oxidized, wet, cool (<850°C), Sr-and Al-rich, and Fe-poor. These silicic rocks are
interpreted to have been derived from mafic parent magmas generated by dehydration of oceanic lithosphere and melting in the
mantle wedge above a subduction zone. Plagioclase fractionation was minimized by the high water fugacity and oxide precipitation
was enhanced by high oxygen fugacity. This resulted in the formation of Si-, Al-, and Sr-rich differentiates with low Fe/Mg
ratios, relatively low temperatures, and declining densities. Magma mixing, large proportions of crustal assimilation, and
polybaric crystal fractionation were all important processes in generating this Oligocene suite. In contrast, most of the
rhyolites of the Snake River Plain are alkaline to calc-alkaline, ferroan, reduced, dry, hot (830–1,050°C), Sr-and Al-poor,
and Nb-and Fe-rich. They are part of a distinctly bimodal sequence with tholeiitic basalt. These characteristics were largely
imposed by their derivation from parental basalt (with low fH2O and low fO2) which formed by partial melting in or above a mantle plume. The differences in intensive parameters caused early precipitation
of plagioclase and retarded crystallization of Fe–Ti oxides. Fractionation led to higher density magmas and mid-crustal entrapment.
Renewed intrusion of mafic magma caused partial melting of the intrusive complex. Varying degrees of partial melting, fractionation,
and minor assimilation of older crust led to the array of rhyolite compositions. Only very small volumes of distinctive rhyolite
were derived by fractional crystallization of Fe-rich intermediate magmas like those of the Craters of the Moon-Cedar Butte
trend.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
‘Snake River (SR)-type’ volcanism at the Yellowstone hotspot track: distinctive products from unusual,high-temperature silicic super-eruptions 总被引：1，自引：0，他引：1
M. J. Branney B. Bonnichsen G. D. M. Andrews B. Ellis T. L. Barry M. McCurry 《Bulletin of Volcanology》2008,70(3):293-314
A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive
volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern
Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous
and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) large-volume,
lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarse-grained
ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre;
(3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development
of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary
lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association
between the rhyolitic rocks and numerous, coalescing low-profile basalt lava shields; and (8) widespread evidence of emplacement
in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic
hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many
rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6–8), and involved H2O-poor, low-δ18O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900–1,050°C). SR-type
volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with
pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme,
and the rhyolite extrusions are small volume silicic domes and coulées. SR-type volcanism seems to have occurred at numerous
times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos
Texas, Etendeka-Paraná, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea
Dacite of Australia.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
6.
Precipitation data are important for hydrometeorological analyses, yet there are many ways to measure precipitation. The impact of station density analysed by the current study by comparing measurements from the Missouri Mesonet available via the Missouri Climate Center and Community Collaborative Rain, Hail, and Snow (CoCoRaHS) measurements archived at the program website. The CoCoRaHS data utilize citizen scientists to report precipitation data providing for much denser data resolution than available through the Mesonet. Although previous research has shown the reliability of CoCoRaHS data, the results here demonstrate important differences in details of the spatial and temporal distribution of annual precipitation across the state of Missouri using the two data sets. Furthermore, differences in the warm and cold season distributions are presented, some of which may be related to interannual variability such as that associated with the El Niño and Southern Oscillation. The contradictory results from two widely‐used datasets display the importance in properly choosing precipitation data that have vastly differing temporal and spatial resolutions. With significantly different yearly aggregated precipitation values, the authors stress caution in selecting 1 particular rainfall dataset as conclusions drawn could be unrepresentative of the actual values. This issue may be remediated by increased spatiotemporal coverage of precipitation data. 相似文献
7.
Graham D. M. Andrews Michael J. Branney Bill Bonnichsen Michael McCurry 《Bulletin of Volcanology》2008,70(3):269-291
The 80 km long NNE-trending Rogerson Graben on the southern margin of the central Snake River Plain, Idaho, USA, hosts a rhyolitic
pyroclastic succession, 200 m thick, that records a period of successive, late-Miocene, large-volume explosive eruptions from
the Yellowstone–Snake River Plain volcanic province, and contemporaneous extension. The succession, here termed the Rogerson
Formation, comprises seven members (defined herein) and records at least eight large explosive eruptions with numerous repose
periods. Five high-grade and extremely high-grade ignimbrites are intercalated with three non-welded ignimbrites and two volcaniclastic
deposits, with numerous repose periods (palaeosols) throughout. Two of the ignimbrites are dominantly rheomorphic and lava-like
but contain subordinate non-welded pyroclastic layers. The ignimbrites are typical Snake River Plain high-silica rhyolites,
with anhydrous crystal assemblages and high inferred magmatic temperatures (≤ 1,025°C). We tentatively infer that the Jackpot
and Rabbit Springs Members may have been emplaced from the Bruneau–Jarbidge eruptive centre on the basis of: (1) flow lineation
trends, (2) crystal assemblage, and (3) radiometric age. We infer that the overlying Brown’s View, Grey’s Landing, and Sand
Springs Members may have been emplaced from the Twin Falls eruptive centre on the basis of: (1) kinematic indicators (from
the east), and (2) crystal assemblage. Furthermore, we have established the contemporaneous evolution of the Rogerson Graben
from the emplacement of the Jackpot Member onwards, and infer that it is similar to younger half-graben along the southern
margin of the Snake River Plain, formed by local reactivation of Basin and Range structures by the northeastwardly migration
of the Yellowstone hot-spot.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
9.
Can crystallization of olivine tholeiite give rise to potassic rhyolites?—an experimental investigation 总被引：6，自引：0，他引：6
Matthew L. Whitaker Hanna Nekvasil Donald H. Lindsley Michael McCurry 《Bulletin of Volcanology》2008,70(3):417-434
Experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica-saturated potassic suites
could be genetically related through crystallization. Extreme crystallization (96–97%) of a high-MgO (10.62 wt%) olivine tholeiite
from the Snake River Plain with an initial bulk water content of 0.4 wt% at a mid-crustal pressure of 4.3 kbar generated potassic
rhyolitic liquids similar in major element chemistry to those found in the Quaternary rhyolite domes of the Snake River Plain
and their plutonic equivalents in the Proterozoic Laramie Anorthosite Complex. Residual liquids comparable in composition
to the bulk rock compositions of intermediate rocks found at the Craters of the Moon and Cedar Butte eruptive centers in the
Snake River Plain are also generated along this crystallization path.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
10.
Radar accuracy in estimating qualitative precipitation estimation at distances larger than 120 km degrades rapidly because of increased volume coverage and beam height. The performance of the recently upgraded dual‐polarized technology to the NEXRAD network and its capabilities are in need of further examination, as improved rainfall estimates at large distances would allow for significant hydrological modelling improvements. Parameter based methods were applied to radars from St. Louis (KLSX) and Kansas City (KEAX), Missouri, USA, to test the precision and accuracy of both dual‐ and single‐polarized parameter estimations of precipitation at large distances. Hourly aggregated precipitation data from terrestrial‐based tipping buckets provided ground‐truthed reference data. For all KLSX data tested, an R(Z,ZDR) algorithm provided the smallest absolute error (3.7 mm h?1) and root‐mean‐square‐error (45%) values. For most KEAX data, R(ZDR,KDP) and R(KDP) algorithms performed best, with RMSE values of 37%. With approximately 100 h of precipitation data between April and October of 2014, nearly 800 and 400 mm of precipitation were estimated by radar precipitation algorithms but was not observed by terrestrial‐based precipitation gauges for KLSX and KEAX, respectively. Additionally, nearly 30 and 190 mm of measured precipitation observed by gauges were not detected by the radar rainfall estimates from KLSX and KEAX, respectively. Results improve understanding of radar based precipitation estimates from long ranges thereby advancing applications for hydrometeorological modelling and flood forecasting. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献