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首页> 外文期刊>Geographical Research >Geomorphic reconstruction of formation and recession processes of waterfalls of the Kaminokawa river basin on Osumi Peninsula, southern Kyushu, Japan
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Geomorphic reconstruction of formation and recession processes of waterfalls of the Kaminokawa river basin on Osumi Peninsula, southern Kyushu, Japan

机译：日本九州南部大须半岛上河上川河流域瀑布形成与衰退过程的地貌重建

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摘要

To assess the geomorphological importance of waterfall recession in volcanic bedrock, we examined recession rates of six waterfalls in the lower reaches of Kaminokawa river basin on the Osumi Peninsula in southern Kyushu. The examination was performed with an empirical equation that uses a dimensionless parameter obtained by dimensional analysis of relevant measured factors, including erosive force, size of waterfall, and bedrock resistance. Welded Ata ignimbrite, formed at approximately 110ka, may have played an initiating role to maintain such waterfalls because it resists weathering more than other local rocks. Estimated recession rates for the six waterfalls range from 0.2 to 3.0cm/y, which compare with estimated rates for waterfalls in another region characterised by welded ignimbrite. Comparison of equation-derived recession rates of waterfalls with actual recession distances from confluences supports the idea that an original waterfall will subsequently split into two distinct waterfalls when it recesses past an upstream junction of two channels. Our findings revealed that all six waterfalls likely would have been at almost the same point lower in the watershed in the past, marking the general site of the original waterfall. Moreover, the ancestral original waterfall is highly likely to have started from a point between the caldera rim and present river mouth. There, a knickpoint was likely caused by the river dropping into an inner part of the caldera, possibly just after the eruption of the Ata ignimbrite. The waterfall erodes upstream away from the caldera basin, and this happens to be to the east.
机译：为了评估火山岩基岩中瀑布后退的地貌学重要性，我们研究了九州南部大s半岛上河上川流域下游六个瀑布的后退率。使用经验方程式进行检查，该方程式使用通过对相关测量因子（包括侵蚀力，瀑布的大小和基岩阻力）进行尺寸分析而获得的无量纲参数。焊接的Ata火成岩形成于大约110ka，可能起了维持这种瀑布的作用，因为它比其他本地岩石更能抵抗风化。六个瀑布的估计衰退率范围为0.2到3.0cm / y，与另一个以焊接的火成岩为特征的区域的估计衰退率相比。将瀑布方程式的衰退速率与汇合处的实际衰退距离进行比较，可以支持这样的想法，即原始瀑布经过两个通道的上游交汇处后将随后分成两个不同的瀑布。我们的发现表明，过去所有6个瀑布可能都位于分水岭的几乎同一位置，这标志着原始瀑布的总体位置。此外，祖先的原始瀑布很有可能是从火山口边缘和当前河口之间的一点开始的。在那儿，很可能是由于河流落入破火山口内部而造成的一个拐点，可能是在Ata火成岩喷发之后。瀑布从火山口流域向上游侵蚀，恰好在东部。

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