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Lithologic control of debris torrent occurrence 总被引：1，自引：0，他引：1
A field-based investigation into the frequency and magnitude of debris torrent systems reveals that lithology controls the spatial and temporal occurrence of debris torrents in the Tsitika Watershed, Vancouver Island, British Columbia. We identified 125 debris torrent systems in the watershed; for half these basins we used dendrochronology, historical air photographs, and field surveys to estimate debris torrent frequency and magnitude for a 30 year period. We find that the volcaniclastic half of the watershed contains more than twice as many debris torrent systems, in which debris torrents occur over seven times more frequently, and the deposits have a higher rate of delivery of sediment to the mainstem river than the intrusive half. Lithologic differences in weathering rates, weathering product grain size, and rock texture can explain the observed differences in debris torrent behaviour. Because debris torrents are the main sediment transport path from hilltop to valley bottom in the region, these results confirm an important lithologic control on regional sediment transport. While the exact numbers are uncertain, we estimate that the sediment flux of volcaniclastic debris torrents in the watershed is five times higher than that of the intrusive debris torrents. 相似文献
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Sterling L. Levie Jr. 《Earth, Moon, and Planets》1971,3(3):315-325
A set of twenty-one point masses gravitationally equivalent to the L1 lunar potential model is presented. By construction, the equivalence is valid only in a region of space sampled by Apollo spacecraft. That region is taken to be a finite, torus-shaped shell. When used in place of the L1 model for Apollo 12 lunar orbit determination, the solution set gives spacecraft positions identical to within about 100 m.The solution is developed in two steps: first the L1 potential is examined to determine favorable mass locations, and then the mass values are computed to force an optimum matching of the L1 potential. Therefore the solution set is artificial. It is related to the Moon's actual mass distribution only in its similar gravitational effects in a limited region of space. 相似文献
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D. F. Webb H. Cremades A. C. Sterling C. H. Mandrini S. Dasso S. E. Gibson D. A. Haber R. W. Komm G. J. D. Petrie P. S. McIntosh B. T. Welsch S. P. Plunkett 《Solar physics》2011,274(1-2):57-86
The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected ??heliophysical?? system during this solar minimum, centered on Carrington Rotation 2068, March 20??C?April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. But during the first half of CR 2068 three solar active regions flanked by two opposite-polarity, low-latitude coronal holes were present. These departures from the quiet Sun led to both eruptive activity and solar wind structure. Most of the eruptive activity, i.e., flares, filament eruptions and coronal mass ejections (CMEs), occurred during this first, active half of the interval. We determined the source locations of the CMEs and the type of associated region, such as active region, or quiet sun or active region prominence. To analyze the evolution of the events in the context of the global solar magnetic field and its evolution during the three rotations centered on CR 2068, we plotted the CME source locations onto synoptic maps of the photospheric magnetic field, of the magnetic and chromospheric structure, of the white light corona, and of helioseismological subsurface flows. Most of the CME sources were associated with the three dominant active regions on CR 2068, particularly AR 10989. Most of the other sources on all three CRs appear to have been associated with either isolated filaments or filaments in the north polar crown filament channel. Although calculations of the flux balance and helicity of the surface magnetic features did not clearly identify a dominance of one region over the others, helioseismological subsurface flows beneath these active regions did reveal a pronounced difference among them. These preliminary results suggest that the ??twistedness?? (i.e., vorticity and helicity) of subsurface flows and its temporal variation might be related to the CME productivity of active regions, similar to the relationship between flares and subsurface flows. 相似文献
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We amassed statistics for quiet-sun chromosphere spicules at the limb using ground-based observations from the Swedish 1-m Solar Telescope on La Palma and simultaneously from NASA’s Transition Region and Coronal Explorer (TRACE) spacecraft. The observations were obtained in July 2006. With the 0.2 arcsecond resolution obtained after maximizing
the ground-based resolution with the Multi-Object Multi-Frame Blind Deconvolution (MOMFBD) program, we obtained specific statistics
for sizes and motions of over two dozen individual spicules, based on movies compiled at 50-second cadence for the series
of five wavelengths observed in a very narrow band at Hα, on-band and at ± 0.035 nm and ± 0.070 nm (10 s at each wavelength)
using the SOUP filter, and had simultaneous observations in the 160 nm EUV continuum from TRACE. The MOMFBD restoration also
automatically aligned the images, facilitating the making of Dopplergrams at each off-band pair. We studied 40 Hα spicules,
and 14 EUV spicules that overlapped Hα spicules; we found that their dynamical and morphological properties fit into the framework
of several previous studies. From a preliminary comparison with spicule theories, our observations are consistent with a reconnection
mechanism for spicule generation, and with UV spicules being a sheath region surrounding the Hα spicules. 相似文献
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Frank I. González Vasily V. Titov Harold O. Mofjeld Angie J. Venturato R. Scott Simmons Roger Hansen Rodney Combellick Richard K. Eisner Don F. Hoirup Brian S. Yanagi Sterling Yong Mark Darienzo George R. Priest George L. Crawford Timothy J. Walsh 《Natural Hazards》2005,35(1):89-110
The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers. 相似文献
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Vertical cross contamination of trichloroethylene in a borehole in fractured sandstone 总被引：1，自引：0，他引：1
Boreholes drilled through contaminated zones in fractured rock create the potential for vertical movement of contaminated ground water between fractures. The usual assumption is that purging eliminates cross contamination; however, the results of a field study conducted in a trichloroethylene (TCE) plume in fractured sandstone with a mean matrix porosity of 13% demonstrates that matrix-diffusion effects can be strong and persistent. A deep borehole was drilled to 110 m below ground surface (mbgs) near a shallow bedrock well containing high TCE concentrations. The borehole was cored continuously to collect closely spaced samples of rock for analysis of TCE concentrations. Geophysical logging and flowmetering were conducted in the open borehole, and a removable multilevel monitoring system was installed to provide hydraulic-head and ground water samples from discrete fracture zones. The borehole was later reamed to complete a well screened from 89 to 100 mbgs; persistent TCE concentrations at this depth ranged from 2100 to 33,000 microg/L. Rock-core analyses, combined with the other types of borehole information, show that nearly all of this deep contamination was due to the lingering effects of the downward flow of dissolved TCE from shallower depths during the few days of open-hole conditions that existed prior to installation of the multilevel system. This study demonstrates that transfer of contaminant mass to the matrix by diffusion can cause severe cross contamination effects in sedimentary rocks, but these effects generally are not identified from information normally obtained in fractured-rock investigations, resulting in potential misinterpretation of site conditions. 相似文献
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