Abrasion-set limits on Himalayan gravel flux
Abrasion-set limits on Himalayan gravel flux
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DOI：
10.1038/nature22039
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发表时间：
2017-04-27
期刊：
影响因子：
64.8
通讯作者：
Sinclair, Hugh D.
中科院分区：
文献类型：
--
作者：
Dingle, Elizabeth H.;Attal, Mikael;Sinclair, Hugh D.
来自喜马拉雅山脉的河流携带着地球上最大的沉积物负荷（1），但这些河流中的粗砾石在进入恒河平原（包含恒河的北印度河平原的一部分）后约10-40公里内消失。了解砾石的命运对于预测河流对地震或风暴引发的大量沉积物流入的反应非常重要。1999年集集地震和2008年汶川地震（2-7）后，砾石流量迅速增加，随后河床淤积（即河流沉积物）减少了河道容量，增加了洪水淹没（3）。在这里，我们提出了在恒河盆地的扇的几何形状，沉积物粒度和岩性的分析。我们发现，从喜马拉雅山脉中部排水的河流的砾石通量，上游集水面积约为350至50，000平方公里，是可比的。我们的研究结果表明，在河流运输过程中的砾石磨损可以解释这一观察，大部分的砾石来源超过100公里上游转化为沙子的时候，它到达恒河平原。这些发现表明，来自大喜马拉雅山脉的地震引起的沉积物脉冲，例如2015年廓尔喀地震（8）之后的沉积物脉冲，不太可能导致山前砾石淤积增加。相反，我们认为，沉积物涌入应导致在一个升高的沙通量，导致不同的模式，在人口稠密，低救济恒河平原的淤积和洪水风险。
Rivers sourced in the Himalayan mountain range carry some of the largest sediment loads on the planet(1), yet coarse gravel in these rivers vanishes within approximately 10-40 kilometres on entering the Ganga Plain (the part of the North Indian River Plain containing the Ganges River). Understanding the fate of gravel is important for forecasting the response of rivers to large influxes of sediment triggered by earthquakes or storms. Rapid increase in gravel flux and subsequent channel bed aggradation (that is, sediment deposition by a river) following the 1999 Chi-Chi and 2008 Wenchuan earthquakes(2-7) reduced channel capacity and increased flood inundation(3). Here we present an analysis of fan geometry, sediment grain size and lithology in the Ganga Basin. We find that the gravel fluxes from rivers draining the central Himalayan mountains, with upstream catchment areas ranging from about 350 to 50,000 square kilometres, are comparable. Our results show that abrasion of gravel during fluvial transport can explain this observation; most of the gravel sourced more than 100 kilometres upstream is converted into sand by the time it reaches the Ganga Plain. These findings indicate that earthquake-induced sediment pulses sourced from the Greater Himalayas, such as that following the 2015 Gorkha earthquake(8), are unlikely to drive increased gravel aggradation at the mountain front. Instead, we suggest that the sediment influx should result in an elevated sand flux, leading to distinct patterns of aggradation and flood risk in the densely populated, low-relief Ganga Plain.