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31.
At Gross Brukkaros a central depression has developed within domed Nama Group sediments and has functioned as a local depocenter, with a primary fill deposited during the Cretaceous and a small secondary fill by alluvial fans during the Tertiary and Quaternary. The diameter of the entire structure is about 10 km and that of the central depression is about 3 km. Within this depocenter the sedimentary sequence consists mainly of debris-flow and mudflow deposits, with minor intercalations of fluviatile (braided channel) sediments and fossiliferous lacustrine deposits. The sedimentary system represents a set of coalesced subaerial fans which formed a fringing sedimentary apron along the margin of the depocenter. This sedimentary apron passed distally and centrally into a permanent lake, which was characterized by a fluctuating water level. Facies transitions observed are typical of those described from modern and ancient fan delta systems. Contact relationships show the Gross Brukkaros sediments to be about the same age (Upper Cretaceous) as the surrounding carbonatitic volcanism. An Upper Cretaceous age is also consistent with the plant fossil association recently recognized within the lacustrine beds of Gross Brukkaros. We attribute the genesis of the dome structure to the shallow intrusion of a laccolith-shaped, strongly alkaline to carbonatitic magma body. Subsequent depletion of the reservoir due to volcanic activity around and in(?) Gross Brukkaros led to subsidence resulting in the development of the Gross Brukkaros depocenter. Differences between Gross Brukkaros and the general caldera model consist of a radially oriented dike pattern and the formation of the caldera by downsagging rather than cauldron subsidence, as derived from the absence of ring faults and ring dikes. The first (radial dikes) may be attributed to comparatively strong initial doming; the latter (lack of ring faults) to the small size of the caldera, its incremental subsidence, and finally the sedimentary wall rocks instead of a rigid crystalline crust. 相似文献
32.
传统的观点认为山区泥石流灾害的形成主要取决于降水,其产汇流运动的过程是可采用水文过程模拟的物理过程。基于目前泥石流灾害集中分布于地震带和干旱河谷的现象以及现有的泥石流形成与防治研究基础,我们发现在人类居住与活动的山区,其坡度和降水极易满足泥石流灾害的形成条件,因此物源控制着泥石流灾害的孕育、形成和演化,主宰了灾害性泥石流的过程。物源的动态变化改变了泥石流发育的难易程度,主导了泥石流的规模和频率变化。泥石流物源在内外动力作用下经历松散化或密实化两个不同的演化过程,不同密度的土体通过剪缩或剪胀形成不同规模、频率与性质的泥石流。此外物源也控制了泥石流的规模放大过程。实践证明基于物源控制理论的区域预测、分级多指标预警和工程调控技术是科学有效的。因此,灾害性泥石流是一个地质作用主导的地质过程,该过程的特征描述需要更多地考虑基于地质环境条件的经验模型,且高效能的灾害预测预警与调控需要基于物源控制的机理和过程而进行。 相似文献
33.
浙江桐庐地区上奥陶统堰口组主要为一套灰色细砂岩、粉砂岩与深灰色-灰黑色泥岩、粉砂质泥岩的韵律性薄互层, 底部发育2～3层灰色中-厚层的砾岩, 其砂泥岩薄互层中发育有典型的脉状、波状和透镜状层理及韵律层理。这种砾岩过去一直被认为是底砾岩, 其上的砂泥岩韵律性薄互层被认为是典型的古代潮坪沉积。野外调查并结合区域地质资料分析结果表明, 堰口组沉积环境应为较深水斜坡环境,而非浅水海岸环境;其底部的砾岩应为富基质的碎屑流沉积,而不应是底砾岩;中上部的砂泥岩韵律性薄互层应为较深水斜坡上的内潮汐沉积,而不是浅水潮坪沉积。这一内潮汐沉积具有典型的对偶层双向递变层序, 可能为内潮汐的大潮和小潮周期性变化的结果,这是在中国首次识别出的古代内潮汐沉积。 相似文献
34.
The Saharan debris flow: an insight into the mechanics of long runout submarine debris flows 总被引：6，自引：0，他引：6
New 3·5 kHz profiles and a series of piston cores from the north-west African margin provide evidence that the Saharan debris flow travelled for more than 400 km on a highly fluid, low-friction layer of poorly sorted sediment. Data suggest that the Saharan debris flow is a two-phase event, consisting of a basal, volcaniclastic debris flow phase overlain by a pelagic debris flow phase. Both phases were emplaced on the lower continental rise by a single large debris flow at around 60 ka. The volcaniclastic flow left a thin deposit less than 5 m thick. This contrasts with the much thicker (over 25 m) deposit left by the pelagic debris flow phase. We suggest that pelagic sediment, sourced and mobilized as debris flow from the African continental margin, loaded and destabilized volcaniclastic material in the vicinity of the western Canaries. When subjected to this loading, the volcaniclastic material appears to have formed a highly fluid sandy debris flow, capable of transporting with it the huge volumes of pelagic debris, and contributing to a runout distance extending over 400 km downslope of the Canary Islands on slopes that decrease to as little as 0·05°. It is likely that the pelagic debris formed a thick impermeable slab above the volcanic debris, thus maintaining high pore pressures generated by loading and giving rise to low apparent friction conditions. The distribution of the two debris phases indicates that the volcaniclastic debris flow stopped within a few tens of kilometres after escaping from beneath the pelagic debris flow, probably because of dissipation of excess pore pressure when the seal of pelagic material was removed. 相似文献
35.
深海相中的砂质碎屑流沉积：以西藏特提斯喜马拉雅侏罗—白垩系为例 总被引：7，自引：1，他引：6
阐述了砂质碎屑流沉积特征、研究现状及其与其他深海碎屑沉积的区别,认为西藏特提斯喜马拉雅上休罗统－下白垩统深海沉积背景下的块状砂岩具有砂质碎屑流沉积性质,指出深海相中的块状砂岩可以预测。 相似文献
36.
Some of the soils on the floors of dry chalkland valleys north of the River Thames in the Marlow area have surface horizons of moderately to very flinty, weakly or non-calcareous, poorly sorted loams, which were deposited in the late Holocene. These overlie typical chalkland gelifluction and periglacial fluvial deposits. Fine calcareous colluvial loams also occur but are less common than in valleys elsewhere on the English chalk. Particle size and mineralogical analyses suggest that the loamy matrix of the flinty surface horizons was derived from loess and early Tnames terrace deposits or Clay-with-flints occurring on interfluves between the dry-valleys. On the evidence of their poorly sorted nature, lack of carbonate, abundance of large flints and irregularly ridged surfaces, it is suggested that they originated mainly as valley-side debris flows. 相似文献
37.
This paper proposes an extension of methods used to predict the propagation of landslides having a long runout to smaller landslides with much shorter propagation distances. The method is based on: (1) a depth-integrated mathematical model including the coupling between the soil skeleton and the pore fluids, (2) suitable rheological models describing the relation between the stress and the rate of deformation tensors for fluidised soils and (3) a meshless numerical method, Smooth Particle Hydrodynamics, which separates the computational mesh (or set of computational nodes) from the mesh describing the terrain topography, which is of structured type – thus accelerating search operations. The proposed model is validated using two examples for which there are analytical solutions, and then it is applied to two short runout landslides which happened in Hong Kong in 1995, for which there is available information. 相似文献
38.
Sophia Zubrycky Andrew Mitchell Scott McDougall Alex Strouth John J. Clague Brian Menounos 《地球表面变化过程与地形》2021,46(12):2395-2413
Predicting the spatial impact of debris flows on fans is challenging due to complex runout behaviour. Debris flow mobility is highly variable and flows can sporadically avulse the channel. For hazard and risk assessments, practitioners typically base the probability of spatial impact or avulsion on their experience and expert judgement. To support decision-making with empirical observations, we studied spatial impact distributions on 30 active debris-flow fans in south-western British Columbia, Canada. We mapped 146 debris-flow impact areas over an average observation period of 74 years using orthorectified airphotos, satellite imagery, topographic base maps, LiDAR data, orthophotos, and field observations. We devised a graphical method to convert our geospatial mapping into spatial impact heat maps normalized by fan boundaries, enabling comparison of runout distributions across different fans. About 90% of the mapped debris flows reached beyond the mid-points of fans, while less than 10% avulsed more than half-way across the fan relative to the previous flow path. Most avulsions initiated at distances of 20% to 40% of the maximum fan length from the fan apex and upstream of the fan intersection point. Large volume events tend to be more mobile in the down-fan direction, but the relation between volume and cross-fan runout (e.g., avulsions) is more complex. Differences in spatial impact distributions can be explained, in part, by the degree of fan incision and whether a fan is truncated at its toe by a river or lake. There were no significant differences in spatial impact distributions based on the geology of the source area, sediment supply condition, or hydrogeomorphic process classification. 相似文献
39.
川藏铁路加查至朗县段位于青藏高原东南部雅鲁藏布江中游,地形地貌复杂、构造活动强烈,是我国地质灾害高易发区,崩塌、滑坡和泥石流等地质灾害发育密度大、危害严重。在资料收集和遥感解译的基础上,对川藏铁路加查—朗县段的地质灾害进行野外调查,在铁路线两侧各5 km约780 km2范围内发现了崩塌、滑坡和泥石流共139处,沿雅鲁藏布江断裂带新发现拉岗村高速远程滑坡和日阿莫大型滑坡,并研究了该区地质灾害的发育特征和形成机理。调查结果表明：在雅鲁藏布江断裂对区域地貌和岩体结构控制作用下,崩塌、滑坡等地质灾害沿断裂带呈带状密集分布是该区地质灾害发育分布的主要特征之一,约有53%的崩塌滑坡滑动方向垂直于断裂走向,30%的崩塌滑坡与断裂带走向近于平行;在地壳强烈隆升和河流侵蚀作用下,雅鲁藏布江宽谷段和峡谷段的地质灾害发育特征具有明显差异;断裂活动特别是断裂剧烈活动诱发地震导致该区具有高速远程滑坡发生的背景,如拉岗村高速远程滑坡;在断裂活动、降雨、人类工程活动等内外动力耦合作用下该区地质灾害形成机理更加复杂,部分滑坡稳定性差且多次发生活动,给该区重大工程规划建设和防灾减灾造成重要影响。 相似文献
40.
１９９４－０３－２０四川省高县白庙乡芙蓉村白崖（１０４°３９′００″Ｅ，２８°２７′４０″Ｎ）发生崩塌性滑坡。滑坡发生区前后缘海拔分别为１０００和１１００（ｍ）．原始方量约１１０万ｍ￣３岩土物质从坡体剪出后，沿陡坡继续运动，随即解体、破碎，部分碎屑物质形成方量约４０万ｍ￣３的崩积锥；大部岩土物质转化为碎屑流而进入沟道内，后经三次转折，流程约６５０ｍ，形成方量约１００万ｍ￣３的碎屑堆积物，历时约１ｍｉｎ，这场灾害致死１８人，伤３人，造成直接经济损失３００万元。 相似文献