Rivers on ice: do supraglacial streams evolve like bedrock rivers?

冰上渠道(流经冰上的河流)是气候变暖的冰川和冰盖日益常见的特征(Kinglake等人，2016年；Bell等人，2018年；Stokes等人，2019年)。在山地冰川上，这些渠道是融水径流的重要排放途径，也可能有助于连接冰上系统、冰川系统和冰下系统，对冰川流动具有潜在影响。在较大的冰盖和冰架上，冰上水道与冰上湖泊密切相关，其发育和排水可影响冰盖物质平衡(Bell等人，2018年)。也许令人惊讶的是，人们对这些通道是如何随着时间的推移而演变的知之甚少，无论是在融化季节还是在更长的时间尺度上。从表面上看，这些河道在形态和水流动力学方面似乎与河流相似，特别是那些有基岩床的河道，但仍然存在许多问题。例如，我们不知道它们是否具有与河道相同的水力几何形状；是否可以使用为基岩河流创建的模型来模拟它们的侵蚀；或者是否可以成功地预测水流速度。了解这些问题将有助于预测这些系统携带的总流量，从而有助于我们对冰川和冰盖水文学的理解。此外，一个耐人寻味的未知数是，这些可以随着冰川形状的变化而迅速演变的冰上水道，是否可能是基岩河流对更长期的基准面变化做出反应的有用类似物。该项目的目的是了解冰上河道中水流和河道形态之间的相互作用，并确定是否可以使用为基岩河流开发的方法来预测它们的行为。将通过下列目标确定这一目标：--广泛审查关于冰上渠道的文献--利用遥感技术根据各种背景建立一个广泛的渠道形态数据库--对两个野外季节山地冰川上的渠道形态的时空变化进行详细调查--比较冰上渠道的形态和演变是否类似于基岩渠道的类似物。

Supraglacial channels (rivers flowing over ice) are an increasingly common feature of glaciers and ice sheets subjected to a warming climate (Kingslake et al., 2016; Bell et al., 2018; Stokes et al., 2019 ). On mountain glaciers, these channels are important discharge routes for meltwater runoff and may also help connect supraglacial to englacial and subglacial systems, with potential implications for glacier flow. On larger ice sheets and ice shelves, supraglacial channels are closely associated with supraglacial lakes, whose development and drainage can impact on ice sheet mass balance (Bell et al., 2018). Perhaps surprisingly, little is known about how these channels evolve over time, both through melt season and over much longer time-scales. Superficially, these channels appear to be similar to river channels, especially those with bedrock beds, in terms of their morphology and flow dynamics, but many questions remain. For example, we do not know whether they have the same hydraulic geometry as river channels; whether their erosion can be modelled using models created for bedrock rivers; or whether flow velocities can be successfully predicted. Understanding these questions will help predict the total discharge that is carried by these systems and will therefore contribute to our understanding of glacier and ice sheet hydrology. Furthermore, an intriguing unknown is whether these supraglacial channels, which can evolve rapidly to changes in glacier shape, might be useful analogues for bedrock river response to much longer-term base-level changes. The aim of this project is to understand the interactions between flow and channel morphology in supra-glacial channels, and to establish whether their behaviour can be predicted using methods developed for bedrock rivers. This will be established through the following objectives:- Extensive literature review on supraglacial channels- Generate an extensive database of channel morphologies from a range of settings using remote sensing techniques- Undertake a detailed investigation of spatial and temporal changes in channel morphology on a mountain glacier over two field seasons- Comparing whether the morphology and evolution of supraglacial channels is similar to that of bedrock channel analogues.