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1.
This study proposes a tsunami depositional model based on observations of emerged Holocene tsunami deposits in outcrops located in eastern Japan. The model is also applicable to the identification of other deposits, such as those laid down by storms. The tsunami deposits described were formed in a small bay of 10–20-m water depth, and are mainly composed of sand and gravel. They show various sedimentary structures, including hummocky cross-stratification (HCS) and inverse and normal grading. Although, individually, the sedimentary structures are similar to those commonly found in storm deposits, the combination of vertical stacking in the tsunami deposits makes a unique pattern. This vertical stacking of internal structures is due to the waveform of the source tsunamis, reflecting: 1) extremely long wavelengths and wave period, and 2) temporal changes of wave sizes from the beginning to end of the tsunamis.
The tsunami deposits display many sub-layers with scoured and graded structures. Each sub-layer, especially in sandy facies, is characterized by HCS and inverse and normal grading that are the result of deposition from prolonged high-energy sediment flows. The vertical stack of sub-layers shows incremental deposition from the repeated sediment flows. Mud drapes cover the sub-layers and indicate the existence of flow-velocity stagnant stages between each sediment flow. Current reversals within the sub-layers indicate the repeated occurrence of the up- and return-flows.
The tsunami deposits are vertically divided into four depositional units, Tna to Tnd in ascending order, reflecting the temporal change of wave sizes in the tsunami wave trains. Unit Tna is relatively fine-grained and indicative of small tsunami waves during the early stage of the tsunami. Unit Tnb is a protruding coarse-grained and thickest-stratified division and is the result of a relatively large wave group during the middle stage of the tsunami. Unit Tnc is a fine alternation of thin sand sheets and mud drapes, deposited from waning waves during the later stage of the tsunami. Unit Tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout. Cyclic build up of these sub-layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays. 相似文献
2.
Takanobu Oba 《Contributions to Mineralogy and Petrology》1980,71(3):247-256
The join tremolite (Tr)-pargasite (Pa) has been studied in the temperature range 750 °–1,150 ° C under a water vapor pressure
of 1 and 5 kbar. There is a continuous solid solution series between the compositions Tr85Pa15 and TroPa100 at 850 ° C and 5 kbar. Tremolite and pargasite are separated by a solvus at 1 kbar and the field of tremolitic amphibole
+pargasitic amphibole+vapor is present in the region between Tr90Pa10 and Tr10Pa90 at 800 ° C. The phase assemblages at 850 ° C and 1 kbar change as follows with increasing pargasite component; clinopyroxene
+orthopyroxene+quartz+vapor, tremolitic amphibole+vapor, tremolitic amphibole+clinopyroxene +forsterite+plagioclase+vapor,
tremolitic amphibole+pargasitic amphibole+vapor, and pargasitic amphibole+vapor. The petrological significance of amphibole
pairs in metamorphic rocks is discussed on the basis of the experimental results. 相似文献
3.
Discovery of an ice cave in the Yatude Valley, Langhovde, Dronning Maud Land, East Antarctica 总被引：1，自引：0，他引：1
A circular hole was discovered on the downstream side of a glacier dam in the Yatude Valley, Langhovde, East Antarctica, during the 2005–2006 austral summer. The opening of this hole is the first opportunity enabling us to observe the interior of the dam. The opening led to a large cave in the dam, raising the possibility of meltwater drainage through the dam. The Yatude Valley is an approximately U-shaped fluvial valley. The valley floor has been incised to form a box-shaped inner valley that contains fluvial terraces and large boulders upon the valley floor. The origin of these features can be explained by a large amount of running water; however, we consider it unlikely that a regular current has flowed through this site for a long period. Instead, it is more likely that large quantities of lake water have been periodically discharged due to collapse of the glacier dam or spilling out through a tunnel channel within the cave. The discovered hole and the ice cave are key features in understanding the historical development of the Yatude Valley in relation to the melting history of the Antarctic ice sheet. 相似文献
4.
Foraminiferal tests are commonly found in tsunami deposits and provide evidence of transport of sea floor sediments, sometimes from source areas more than 100 m deep and several kilometers away. These data contribute to estimates of the physical properties of tsunami waves, such as their amplitude and period. The tractive force of tsunami waves is inversely proportional to the water depth at sediment source areas, whereas the horizontal sediment transport distance by tsunami waves is proportional to the wave period and amplitude. We derived formulas for the amplitudes and periods of tsunami waves as functions of water depth at the sediment source area and sediment transport distance based on foraminiferal assemblages in tsunami deposits. We applied these formulas to derive wave amplitudes and periods from data on tsunami deposits in previous studies. For some examples, estimated wave parameters were reasonable matches for the actual tsunamis, although other cases had improbably large values. Such inconsistencies probably reflect: (i) local amplification of tsunami waves by submarine topography, such as submarine canyons; and (ii) errors in estimated water depth at the sediment source area and sediment transport distance, which mainly derive from insufficient identification of foraminiferal tests. 相似文献
5.
Takanobu OBA 《Journal of Earth System Science》1990,99(1):81-90
The join tremolite (Tr)-pargasite (Pa) was studied at temperatures between 800 and 1150°C under water vapour pressure of 10 kbar. The results show a continuous solid solution of amphibole between the composition Tr80Pa20 and Pa100 at 800°C and 10kb. Pargasite melts incongruently and breaks down at high temperature to clinopyroxene+forsterite+spinel+L+V. A single phase amphibole with composition lying between Tr80Pa20 and nearly pure Pa, breaks down to amphibole of different composition plus other phases. The stability fields of amphibole spread toward higher temperature side with increasing pargasite content, and pargasite itself has the widest stability field. At subliquidus, the composition of amphibole coexisting with other phases becomes more pargasitic with increasing temperature. The compositions of liquid, which are formed by partial melting of amphibole of Tr40Pa60 composition (Fo-normative) under water vapour pressure of 10 kbar, are alumina-rich and Qz-normative. 相似文献
6.
7.
An assessment of conditions before and after the 1998 Tam Pokhari outburst in the Nepal Himalaya and an evaluation of the future outburst hazard 
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下载免费PDF全文 Damodar Lamsal Takanobu Sawagaki Teiji Watanabe Alton C. Byers Daene C. McKinney 《水文研究》2016,30(5):676-691
On 3 September 1998, a glacial lake outburst flood (GLOF) that originated from Tam Pokhari occurred in the Hinku valley of the eastern Nepal Himalaya. This study analyses the lake's geomorphic and hydrologic conditions prior to the outburst, and evaluates the conditions that could contribute to a future flood through photogrammetric techniques. We processed high‐resolution Corona KH‐4A (2.7 m) and ALOS PRISM (2.5 m) stereo‐images taken before and after the GLOF event, and produced detailed topographic maps (2‐m contour interval) and DEMs (5 m × 5 m). We (re‐) constructed lake water surfaces before (4410 ± 5 m) and after (4356 ± 5 m) the outburst, and reliably estimated the lake water surface lowering (54 ± 5 m) and the water volume released (19.5 ± 2.2 × 106 m3) from the lake, showing good agreement with the results obtained from ground‐based measurements. The most relevant conditions that may have influenced the catastrophic drainage of Tam Pokhari in 1998 include the presence of: (i) a narrow (75 ± 6 m), steep (up to 50°) and high (120 ± 5 m) moraine dam; (ii) high lake level (8 ± 5 m of freeboard) and (iii) a steep overhanging glacier (>40°). The lake outburst substantially altered the immediate area, creating a low and wide (>500 m) outwash plain below the lake, a wide lake outlet channel (~50 m) and a gentle channel slope (~3–5°). Our new data suggest that the likelihood of a future lake outburst is low. Our results demonstrate that the datasets produced by photogrammetric techniques provide an excellent representation of micro‐landform features on moraine dams, lake water surfaces and the changes in both over time, thereby allowing highly accurate pre‐ and post‐GLOF (volumetric) change analysis of glacial lakes. Furthermore, it enables precise measurement of several predictive variables of GLOFs that can be useful for identifying potentially dangerous glacial lakes or prioritizing them for detailed field investigations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
Momentum and Heat Transfer over Urban-like Surfaces 总被引：2，自引：2，他引：0
Momentum and heat transfer was examined for the urban-like surfaces used within the Comprehensive Outdoor Scale MOdel (COSMO)
experiments. Simultaneous and comparative meteorological measurements were made over a pair of scale models with different
block geometries. These data were analyzed to investigate the influence of height variations, obstacle elongation, and packing
density, λ
p
, of blocks on the aerodynamic properties. In addition, the robustness of theoretical expressions of bulk transfer coefficients
for momentum and heat with respect to geometric parameters was examined. Our analyses showed: (1) the theoretical framework
for the bulk transfer coefficient for momentum, C
m
, and that for heat, C
h
, was applicable for homogeneous building arrays, (2) the sensitivity of C
h
to the surface geometry was smaller than that of C
m
, (3) the transfer coefficients were increased by variations of block heights, but not by elongation of blocks, (4) first-order
approximations of C
m
and C
h
for an array of blocks with two different heights can be made by applying simple theoretical assumptions to include the effects
of height variation, and (5) variations of block heights increased the momentum flux significantly, but caused little change
in the sensible heat flux. This can be explained by the feedback mechanism of aerodynamic– thermal interaction; aerodynamic
mixing decreased both the advective velocity and the vertical temperature gradient. 相似文献
9.
Digital terrain modelling using Corona and ALOS PRISM data to investigate the distal part of Imja Glacier, Khumbu Himal, Nepal 总被引：2，自引：2，他引：0
This study used Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM images to generate digital terrain models (DTMs) of the distal part of Imja Glacier,where a few supraglacial ponds (～0.07 km 2) expanded into the large Imja Glacier Lake (Imja Tsho,～0.91 km 2) between 1964 and 2006.DTMs and subsequently derived topographical maps with contour intervals of 1 m were created from the high-resolution images (Corona in 1964 and ALOS in 2006) in the Leica Photogrammetric Suite (LPS) platform.The DTMs and topographic maps provided excellent representation of the elevation and micro-topography of the glacier surface,such as its supra-glacial ponds/lake,surface depressions,and moraine ridges,with an error of about +/-4 m (maximum).The DTMs produced from the Corona and ALOS PRISM images are suitable for use in studies of the surface change of glaciers.The topographical maps produced from the Corona data (1964) showed that part of the dead ice in the down-glacier area was even higher than the top of the lateral moraine ridges,while the glacier surface in the up-glacier area was noticeably lower than the moraine crests.This suggests more extensive melting of glacier ice in the up-glacier area before 1964.The average lowering of the glacier surface from 1964 to 2006 was 16.9 m for the dead-ice area west of the lake and 47.4 m for the glacier surface east of the lake;between 1964 and 2002,the lake surface lowered by 82.3 m.These figures represent average lowering rates of 0.4,1.1,and 2.2 m/year for the respective areas. 相似文献
10.
Takanobu Sawagaki & Kazuomi Hirakawa 《Geografiska Annaler: Series A, Physical Geography》1997,79(4):223-238
The formation of the glacial erosional bedforms at the Soya Coast of Lützow-Holm Bay, East Antarctica is discussed. The streamlined bedforms in the studied area are classified into crescentic transverse ridges and tadpole rocks, and these bedforms are accompanied by small erosional marks (s-forms) which suport the interpretation of subglacial meltwater erosion. Some tadpole rocks are superimposed on a large roche moutonnée, and these two kinds of landform are interpreted to have different modes of formation. Observations and interpretations of these bedforms are used to reconstruct the historical development of the glacial erosional bedforms, and to draw attention to the significance and implications of subglacial meltwater erosion on the marginal area of the Antarctic Ice Sheet in the past. An initial episode of glacial plucking and abrasion produced roches moutonnées and basic large-scale landforms. Subglacial meltwater flowing peiodically into the Lützow-Holm Bay sculptured s-forms and streamlined bedforms in bedrock over much of the area. During this period, except for water-flowing phases, ice again came in contact with the bedrock to form striations superimposed on the s-forms and the hillocks. 相似文献