Knickpoint Migration: Processes, Rates, and Form

尼克点迁移长期以来被认为是河流对基准面突然下降的主要反应机制。由于基准面下降可由构造隆起、气候变化、海平面下降或河流捕获引发，因此在广泛的地质、构造和气候背景下，裂缝点迁移是河道切割和景观演变的一个重要方面。在基准面突然下降之后，分水岭内积极迁移的裂缝点分布设置了已适应新基准面的地貌和未适应新基准面的地貌之间的边界，因此保留了其遗留的切口前形态。因此，随着构造或气候条件的变化，景观响应的时间尺度和沉积物向盆地输送的时间受到上游裂缝点迁移的速度和方式的强烈影响。尽管裂缝点在景观演变中至关重要，但对裂缝点迁移速度和风格的控制却知之甚少。我们建议在新西兰北岛东角的Waipaoa流域进行一项长达18 ka的nickpoint迁徙自然实验。大约在18ka时，沿着Waipaoa干流形成的一波切口形成了上百个裂口点，这些裂口点在废弃的带状阶地上冲积填充物的阶地地层学中有记录。初步地图和航空摄影调查表明，裂缝点迁移速率和形式（弥漫性、陡峭/离散性、瀑布性）在流域内都显示出相当大的变化。将收集、分析和传播有关断裂点迁移过程、速率和类型的重要新数据，这些数据与上游流域面积（流量和沉积物通量）、基岩岩性和断裂点迁移距离有关。怀帕阿是一个生动的例子，展示了我们所生活的景观是多么的动态，以及它是多么容易受到人类干扰，我们致力于开发各级教育模块，包括K-12教学。

Knickpoint migration has long been recognized as a primary mechanism of river response to sudden base-level fall. As base-level fall can be triggered by tectonic upheaval, climatic change, sea-level fall or river capture, knickpoint migration is an important aspect of channel incision and landscape evolution in a wide range of geological, tectonic, and climatic settings. Following a sudden base-level fall, the distribution of actively migrating knickpoints within a watershed sets the boundary between landforms that have adjusted to the new base level and those that have not, and therefore retain their relict, pre-incision form. Consequently, the time scale of landscape response and the timing of sediment deliver to basins following a change in tectonic or climatic conditions is strong influenced by the rate and style of upstream knickpoint migration.Despite the critical importance of knickpoints in landscape evolution, little is known quantitatively about the controls on the rates and styles of knickpoint migration. We propose to exploit a natural experiment in knickpoint migration that has been running for 18 ka in the Waipaoa drainage basin on the East Cape of New Zealand's North Island. Over on hundred knickpoints demarcate the headward advance of a wave of incision initiated along the Waipaoa trunk stream at about 18ka, as recorded in tephra stratigraphy in alluvial fills on abandoned strath terraces. Preliminary map and aerial photography investigation indicates that both knickpoint migration rate and form (diffuse, steep/discrete, waterfall) show considerable variability within the drainage basin. Significant new data on the processes, rates, and styles of knickpoint migration as a function of upstream drainage area (discharge and sediment flux), substrate lithology, and distance of knickpoint migration will be gathered, analyzed, and disseminated. As the Waipaoa is a dramatic example of how dynamic the landscape we live in is, and how susceptible it can be to human disturbance, we are committed to the development of educational modules at all levels, including K-12 instruction.