Enhanced rock‐slope failure following ice‐sheet deglaciation: timing and causes          下载免费PDF全文

Colin K. Ballantyne  Peter Wilson  Delia Gheorghiu  Àngel Rodés 《地球表面变化过程与地形》2014,39(7):900-913

The temporal pattern of rock‐slope failures (RSFs) following Late Pleistocene deglaciation on tectonically stable terrains is controversial: previous studies variously suggest (1) a rapid response due to removal of supporting ice (‘debuttressing’), (2) a progressive decline in RSF frequency, and (3) a millennial‐scale delay before peak RSF activity. We test these competing models through beryllium‐10 (¹⁰Be) exposure dating of five closely‐spaced quartzite RSFs on the Isle of Jura, Scotland, to establish the relationship between timing of failure and those of deglaciation, episodes of rapid warming and periods of rapid glacio‐isostatic uplift. All five dated RSFs occurred at least 720–2240 years after deglaciation, with the probability of failure peaking ~2 ka after deglaciation, consistent with millennial‐scale delay model (3). This excludes debuttressing as an immediate cause of failure, though it is likely that time‐dependent stress release due to deglacial unloading resulted in progressive development of failure planes within the rock. Thaw of permafrost ice in joints is unlikely to have been a prime trigger of failure as some RSFs occurred several centuries after the onset of interstadial warming. Conversely, the timespan of the RSFs coincides with the period of maximum glacio‐isostatic crustal uplift, suggesting that failure was triggered by uplift‐driven seismic events acting on fractured rock masses. Implications of this and related research are: (1) that retreat of the last Pleistocene ice sheets across tectonically‐stable mountainous terrains was succeeded by a period of enhanced rock‐slope failure due to deglacial unloading and probably uplift‐driven seismicity; (2) that the great majority of RSFs in the British Isles outside the limits of Loch Lomond Stadial (= Younger Dryas) glaciation are of Lateglacial (pre‐Holocene) age; and (3) numerous RSFs must also have occurred inside Loch Lomond Stadial (LLS) glacial limits, but that runout debris was removed by LLS glaciers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

A Brownian model for recurrent volcanic eruptions: an application to Miyakejima volcano (Japan)     

Alexander Garcia-Aristizabal  Warner Marzocchi  Eisuke Fujita 《Bulletin of Volcanology》2012,74(2):545-558

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Nitrogen isotope ratios of nitrate as a clue to the origin of nitrogen on the Pacific coast of Japan     

Ryo Sugimoto  Akihide Kasai  Toshihiro Miyajima  Kouichi Fujita 《Continental Shelf Research》2009

To clarify the sources and transformation of NO₃⁻ on the Pacific coast of Japan, observations over the continental shelf were conducted during the summer in 2005 and 2006 when the Kuroshio flowed close to and away from the coastal area, respectively. Below the halocline, there are two prominent salinity peaks that originated in two different waters. In the subsurface layer, the salinity maximum (S_max) was indicative of the Kuroshio Water (KW), while the salinity minimum (S_min) in the middle layer at ∼400 m depth was indicative of the North Pacific Intermediate Water (NPIW). δ¹⁵N_NO3 ranged from 4.1‰ to 5.1‰ with a mean of 4.8±0.4‰ in the deeper water around S_min. Below 50 m depth over the shelf break, δ¹⁵N_NO3 values (3.1±0.8‰ in 2005 and 4.6±0.3‰ in 2006) clearly increased as contribution of NPIW increased in 2006. On the contrary, subsurface δ¹⁵N of NO₃⁻ values (−1.1±0.1‰) remained unchanged in both years, although the contribution of the KW to the subsurface water changed significantly. This suggests that the source of NO₃⁻ has little effect on the δ¹⁵N of NO₃⁻ in this layer. The negative δ¹⁵N values also coincided with the base of the chlorophyll maximum layer suggesting that these isotopic signals must be evidence of active nitrification in the upper layer.  相似文献   

Constraints on the velocity structure beneath the Tornquist-Teisseyre Zone from beam-forming analysis     

Dolors Alsina  Rod Snieder 《Geophysical Journal International》1996,126(1):205-218

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In situ flash X-ray observation of projectile penetration processes and crater cavity growth in porous gypsum target analogous to low-density asteroids     

Minami Yasui  Masahiko Arakawa  Sunao Hasegawa  Yukihiro Fujita  Toshihiko Kadono 《Icarus》2012,221(2):646-657

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Why does the Sea Level Difference between Kushimoto and Uragami Show Periods of Large Meander and Non-Large Meander Paths of the Kuroshio South of Japan?     

Yoshihiko Sekine  Kohichi Fujita 《Journal of Oceanography》1999,55(1):43-51

The sea level difference between Kushimoto and Uragami, located to the west and east of the southern tip of the Kii Peninsula, is relatively large in periods of non-large meander path (nLMP) of the Kuroshio south of Japan in comparison with periods of large meander path (LMP). Based on this clear relationship, the sea level difference between Kushimoto and Uragami has been used as an index showing the periods of nLMP and those of LMP of the Kuroshio south of Japan. It has been pointed out that warm and saline Kuroshio water, separated from the main path of the Kuroshio, has a tendency to approach the western area off Kii Peninsula to off Muroto Peninsula in periods of nLMP, while it approaches the eastern area off Kii Peninsula to Omae-zaki in periods of LMP. On the basis of this observational evidences, the dynamic background underlaying the well-known relationship between the Kuroshio path and the sea level difference between Kushimoto and Uragami is examined in the present study, using the temperature and salinity data observed by Wakayama Prefectural Fisheries Experimental Station and Fisheries Research Institute of Mie. It is shown that deviations in vertically integrated specific volume off Kushimoto and Uragami almost equal deviations in observed sea level at Kushimoto and Uragami, respectively. It is also shown that the difference in vertically integrated specific volume between off Kushimoto and off Uragami almost equals the difference in observed sea level between Kushimoto and Uragami. As for the Kuroshio water, the high-temperature contribution is predominant for its specific volume rather than that of high salinity, which yields thermal expansion in comparison with coastal water. Because the difference in vertically integrated specific volume between off Kushimoto and off Uragami almost equals the difference in observed sea level between Kushimoto and Uragami, it is concluded that the relationship between the Kuroshio path and sea level difference between Kushimoto and Uragami is caused by the different approaching of the warm Kuroshio water between in nLMP periods and in LMP periods.  相似文献   

Mass-balance Measurements in Alaska and Suggestions for Simplified Observation Programs     

Dennis C. Trabant  & Rod S. March 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):777-789

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Development of new sensor systems for continuous bedload monitoring using a submerged load‐cell system (SLS)          下载免费PDF全文

Takahiro Itoh  Takahiko Nagayama  Rei Utsunomiya  Masaharu Fujita  Daizo Tsutsumi  Shusuke Miyata  Takahisa Mizuyama 《地球表面变化过程与地形》2018,43(8):1689-1700

It is important to evaluate bedload discharge and temporal changes of the bed surface, and bed deformation can be estimated during floods if the bedload discharge is properly evaluated in an arbitrary cross‐section. With the exception of grain size and its distribution within the bedload, bedload discharge has been measured using both direct and indirect methods. Bedload slot is a direct method but cannot be used to measure bedload during a flood because of volume limitations. Indirect methods require correlation between the signals and sediment volume measured using another method. In the present study, a small, automatically recording bedload sensor with an iron plate and a pair of load cells is developed in order to evaluate not only large particles but also sand particles as bedload. Bedload mass is calculated by integrating with respect to both the velocity of sediment particles and the averaged particle weight as measured by a pair of load cells, and, as an example, the velocity is estimated by the cross‐correlation function of weights measured by load cells. The applicability of the proposed sensor is discussed based on the results of flume tests in the laboratory (2014) and the observation flume of the Hodaka Sedimentation Observatory of Kyoto University in Japan (2015). The system was installed in the observation flume in November of 2012, and flume data were obtained using natural sediment particles. In particular, it was difficult to estimate the velocity of averaged bedload particles, and it was better to apply a cross‐correlation function in the laboratory tests. However, it appears that the previous estimation can estimate these velocities in the observation flume using a connecting tube and submerged load‐cell systems. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献