How do rivers respond to uplift? A study of river transience.

自从大约1万年前覆盖了北方欧洲大部分地区的大冰原消退以来，陆地表面一直在上升。这种被称为冰川反弹的上升在斯堪的纳维亚半岛最为迅速。沿着波的尼亚湾的海岸每年上升几毫米，这是一个在人的一生中很容易注意到的速度。因此，瑞典的东部海岸线向大海延伸，几个世纪以来，渔村不得不不断“搬迁”以跟上步伐。该项目旨在了解冰川反弹对景观的影响，特别是对河流的影响。为了应对反弹，瑞典的大河侵蚀了河床，随着时间的推移形成了深河峡谷。这些峡谷是河流进行的一系列调整的一部分，这些调整是为了最大限度地提高河流在其下方上升时侵蚀景观的能力。瀑布，也被称为断点，是这个过程的一个共同特征。如果河流有足够的能量，瀑布可能会侵蚀河床并向上游迁移。量化这种迁移的速度是该项目的主要目标之一，因为这表明景观对冰川反弹的反应有多快。有些瀑布每年迁移数毫米。我以前的研究发现，瀑布迁移的速度取决于河流的流速：强大的河流侵蚀得很快，而小河流的侵蚀很少。另一个主要目标是确定哪些其他因素控制着断点迁移的速度。当缺口点向上游迁移时，它们留下了高高的废弃河道。这些基岩残留物，被称为斯特拉特阶地，将用于通过一种相对较新的技术来确定断点后退的速度。当岩石受到来自外太空的宇宙射线轰击时，矿物中就会产生“宇宙成因核素”。这种产量随着岩石表面以下的深度而减少。通过测量样品中宇宙成因核素的数量，可以估计岩石表面的年龄，因为宇宙成因核素的积累速度与岩石在表面的时间成正比，与侵蚀速度成反比。从河流和斯特拉特阶地收集的数据稍后将用于试图模拟河流侵蚀过程的数值模型。这是有用的，因为由此产生的模型可以应用于其他地方的河流和景观，以了解河流如何响应隆起的基本物理原理。对于该项目的这一部分，NERC研究员将访问格勒诺布尔的约瑟夫傅立叶大学，与数值建模方面的领先专家Peter货车der比克教授合作。

Since the retreat of the great ice-sheet that covered most of northern Europe about 10,000 years ago, the land surface has been uplifting. This uplift, known as glacial rebound, is most rapid in Scandinavia. Along the coast of the Gulf of Bothnia uplift is measured in several millimetres per year/a rate easily noticeable within in a human lifetime. As a result, Sweden's eastern coastline is extending seaward, and over the centuries fishing villages have constantly had to 'relocate' to keep pace. This project is aimed at understanding some of the consequences of the glacial rebound for the landscape in general but particularly for the rivers. In response to the rebound, the large Swedish rivers have eroded their channel beds creating deep river gorges over time. The gorges are part of a set of adjustments the rivers make in order to maximise their ability to erode the landscape as it rises beneath them. Waterfalls, also known as knickpoints, are a common feature of this process. If a river has sufficient energy, a waterfall may erode the channel bed and migrate upstream as it does so. Quantifying the rate of this migration is one of the key aims of the project, because this indicates how fast the landscape is responding to the glacial rebound. Some waterfalls migrate up to several millimetres per year. My previous research has found that the rate of waterfall migration is dependent upon the rate of flow in the river: large, powerful rivers erode rapidly, and small rivers erode very little at all. Determining what other factors control the rate of knickpoint migration is another major aim. As knickpoints migrate upstream they leave high abandoned sections of channel in their wake. These bedrock remnants, known as strath terraces, will be used to determine the rate of knickpoint retreat via a relatively new technique. 'Cosmogenic nuclides' are produced in minerals when rocks are bombarded by cosmic-rays from outer space. This production decreases with depth beneath the rock's surface. By measuring the amount of cosmogenic nuclides in a sample, the age of a rock surface can be estimated, because the amount of cosmogenic nuclides accumulate at a rate proportional to the length of time the rocks have been at the surface, and inversely proportional to the rate of erosion. The data collected from the rivers and strath terraces will later be used in numerical models that attempt to simulate the processes of river erosion. This is useful because the resultant model can be applied to rivers and landscapes elsewhere in order to understand the fundamental physical principles that underlie how rivers respond to uplift. For this part of the project the NERC Fellow will visit Joseph Fourier University, Grenoble, to work with a leading expert in numerical modelling: Prof. Peter van der Beek.