Menier David, Mathew Manoj, Pubellier Manuel, Sapin François, Delcaillau Bernard, Siddiqui Numair, Ramkumar Mu, Santosh M
Université Bretagne Sud, Laboratoire Géosciences Océan, UMR CNRS 6538, rue Yves, Mainguy, 56017, Vannes cedex, France.
Ecole Normale Supérieure UMR 8538 du CNRS, 24 rue Lhomond, 75231, Paris, Cedex 05, France.
Sci Rep. 2017 Mar 28;7(1):457. doi: 10.1038/s41598-017-00620-y.
Empirical models have simulated the consequences of uplift and orographic-precipitation on the evolution of orogens whereas the effects of these forcings on ridgelines and consequent topography of natural landscapes remain equivocal. Here we demonstrate the feedback of a terrestrial landscape in NW Borneo subject to uplift and precipitation gradient owing to orographic effect, and leading to less-predictable flooding and irreversible damages to life and property. Disequilibrium in a large catchment recording the lowest rainfall rates in Borneo, and adjacent drainage basins as determined through χ, a proxy for steady-state channel elevation, is shown to result in dynamic migration of water divide from the windward-side of the orogen towards the leeward-side to attain equilibrium. Loss of drainage area in the leeward-side reduces erosion rates with progressive shortening resulting in an unstable landscape with tectonic uplift, gravity faults and debris flows. C dating of exhumed cut-and-fill terraces reveal a Mid-Pleistocene age, suggesting tectonic events in the trend of exhumation rates (>7 mm a) estimated by thermochronology, and confirmed by morphotectonic and sedimentological analyses. Our study suggests that divide migration leads to lowered erosion rates, channel narrowing, and sediment accretion in intermontane basins on the leeward-side ultimately resulting in enhanced flooding.
经验模型已经模拟了隆升和地形降水对造山带演化的影响，然而这些作用力对山脊线以及自然景观后续地形的影响仍不明确。在此，我们展示了婆罗洲西北部陆地景观的反馈情况，该地区由于地形效应而受到隆升和降水梯度的影响，进而导致洪水的发生难以预测，并对生命和财产造成不可逆转的损害。通过χ（一种代表稳态河道高程的指标）确定的，记录婆罗洲最低降雨率的大型集水区以及相邻流域的不平衡状态，表明分水线会从造山带的迎风侧向背风侧动态迁移以达到平衡。背风侧流域面积的减少会降低侵蚀速率，随着不断缩短，会导致景观不稳定，出现构造隆升、重力断层和泥石流。对挖掘出的填挖阶地进行碳年代测定显示其年龄为中更新世，这表明构造事件与热年代学估计的剥蚀速率趋势（>7毫米/年）一致，并得到了地貌构造和沉积学分析的证实。我们的研究表明，分水线迁移会导致侵蚀速率降低、河道变窄以及背风侧山间盆地的沉积物堆积，最终导致洪水加剧。
