Quantitative Examination of Hummock Alignment in Debris Avalanche Deposits: Zenkoji Debris Avalanche, Usu Volcano, Japan
Quantitative Examination of Hummock Alignment in Debris Avalanche Deposits: Zenkoji Debris Avalanche, Usu Volcano, Japan
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碎片雪崩沉积物中的小丘排列的定量检查：日本有珠火山善光寺碎片雪崩
DOI：
10.4157/geogrevjapanb.83.64
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
Sugai Toshihiko
中科院分区：
文献类型：
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作者：
Y. Hidetsugu;Sugai Toshihiko
残骸雪崩是由灾难性的火山区坍塌造成的。缺乏关于它们相对于碎片雪崩方向的方向的定量数据，这在研究人员中造成了相互矛盾的观点。我们评估了日本USU火山Zenkoji碎屑雪崩堆积物的隆起方向。我们的结果表明，主要沉积区上部的丘陵，即从岩屑雪崩堆积源直接通向中央末端的轴带，倾向于垂直于假定的流动方向排列。然而，沿纵向路径，驼峰对齐有系统地变化。虽然靠近源头的土丘方向垂直于水流方向，但我们注意到，随着距源头距离的增加，逐渐过渡到平行方向。与此同时，边缘地区碎屑雪崩表面以挤压为主的特征上出现了隆起。这些观察结果与以下碎片雪崩运动的情景相一致。首先，对于震源附近的一些大型驼峰，其起源是可以解释的，如下所示。在崩塌时刻，少量的正断层垂直于滑坡方向发展，形成一系列的山脊和地台。然后，随着延伸距离的增加，其他山丘的排列由伸展机制引起，火山附近侵蚀路径的横向约束消失了。随着纵向速度相对于横向速度的进一步增加，驼峰在距离近端区域的距离上变得更加强烈。另一方面，在边缘地区观察到了更分散的隆起方向。这可能是因为它们来自于从主流中排出的沉积物，而不是通过从源头最直接的方式输送。
Debris avalanche hummocks are created by catastrophic volcanic sector collapses. The paucity of quantitative data on their orientation relative to the debris avalanche direction has caused conflicting views among researchers. We evaluated hummock orientation in the Zenkoji debris avalanche deposits at Usu volcano, Japan. Our results show that hummocks within the upper part of the main depositional area, the axial band leading directly from the source to the central extremity of the debris avalanche deposits, tend to be aligned perpendicular to the presumed flow direction. However, hummock alignment varied systematically along the longitudinal path. Although hummocks close to the source were oriented perpendicular to the flow direction, we noted a gradual transition to a parallel orientation with increasing distance from the source. At the same time, hummocks had arisen on compression-dominated features of the debris avalanche surfaces in the marginal areas. These observations are consistent with the following scenario of the debris avalanche movement. To begin with, the origin is explainable for some large-scale hummocks near the source as below. At the moment of collapse, a small number of normal faults develop perpendicular to the landsliding direction, generating a series of ridges and grabens. Then, the alignment of the other hummocks was given rise to by an extensional regime as the runout distance increased and the lateral constraints on the erosional path near the volcano disappeared. As the longitudinal velocity increased further with respect to lateral velocity, hummocks became more strongly aligned at such distances from the proximal area. On the other hand, more-scattered orientations of hummocks have been observed in the marginal areas. This is probably because they were originated from the sediments pushed out of the main flow instead of being transported by the most direct way from the source.