末次冰期河流下切行为对气候变化的响应模式

River Incision Behavior Response to Climate Change During the Last Glacial Period

末次冰期是距离人类最近的一次冰期,气候异常寒冷且存在高频高幅波动,河流系统如何响应冰期气候的变化值得关注与研究。基于河流系统对气候变化的敏感响应,传统的经典地貌理论认为河流下切在河流阶地形成过程中起着至关重要的作用,河流的下切行为发生在间冰期或者冰期向间冰期的过渡阶段,堆积行为发生于冰期,然而近年来最新的河流地貌研究成果表明,末次冰期河流下切较为普遍。首先对河流阶地形成的传统模式进行总结分析,认为单纯的构造驱动模式存在不合理性,气候也发挥着重要的调节作用;单一的气候变化无法驱动多级且高差较大阶地的形成,地壳抬升往往是必要因素;气候变化是引发河流堆积-下切行为转换形成河流阶地的关键因素。其次通过前人的研究案例总结出末次冰期河流下切行为响应气候变化的三种模式:(1)气候的高度不稳定性引发大规模的洪水事件驱动河流快速下切;(2)快速隆升区气候高频波动叠加构造抬升驱动河流下切;(3)沿海平原地区海平面大幅度下降驱动河流下切。这三种模式对于理解末次冰期河流系统对短尺度高频气候变化的响应以及对河流阶地成因的判断具有十分重要的指导意义。

The Last Glacial Period, popularly known as the Ice Age, was the most recent glacial period, which is characterized by high frequency and high amplitude climate fluctuations and unusually cold. How the river system responds to the climate change in this period deserves attention？ According to classical geomorphology theory, the behavior of the river incision occured during the interglacial period or glacial-interglacial transition, while the fluvial aggradation occurred during the glacial period. However, this paper believed that the river incision occurred during the Last Glacial Period is an indisputable fact based on summarizing the research results of river geomorphology in recent years. To begin with, the traditional models of river terrace formation were summarized. The simple tectonic driving model is not reasonable because the climate change plays a very important role. The single climate change cannot drive the formation of multistage and higher elevation terrace, so crustal uplift is a necessary factor. The climate change is a key factor for the formation of river terraces by driving the river fill-cut behavior transition. Three models of the river system response to climate change during＇the Last Glacial Period are summarized ： （ 1 ） massive flooding events caused by high-frequency climate fluctuations drive rapid the river incision; （2）the high-frequency climate fluctuations combining rapid crustal uplift drive the river incision; （3） the coastal plain sea level which drops significantly triggers the river incision. Those models have very important guiding significance of understanding the river system responses to the short-term climate change and the judgment on the origin of river terraces.