Deriving mechanisms and thresholds for cliff retreat in soft-rock cliffs under changing climates: Rapidly retreating cliffs of the Suffolk coast, UK
Deriving mechanisms and thresholds for cliff retreat in soft-rock cliffs under changing climates: Rapidly retreating cliffs of the Suffolk coast, UK
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DOI：
10.1016/j.geomorph.2012.02.007
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发表时间：
2012-06
期刊：
影响因子：
3.9
通讯作者：
S. Brooks;T. Spencer;S. Boreham
中科院分区：
文献类型：
--
作者：
S. Brooks;T. Spencer;S. Boreham
在不断变化的气候条件下，了解软岩悬崖退缩的变化阈值和机制是很重要的。这可以通过结合详细的实地观察、长期过程和形态监测以及数值模拟来实现。北海南部萨福克海岸的悬崖显示出长期（1883-2010年）衰退率为3.5ma−1，在1993-2010年期间上升到4.7ma− 1。每年一年两次的地面调查数据，并应用地理信息系统技术的历史地图和航空摄影的海岸线位置变化的数字化记录，揭示了相当大的十年尺度的变化悬崖衰退，其中嵌套的年际波动率的撤退。关于陆上风及其与高水位（包括风暴潮的发生率）和暴雨事件的相互作用的重要时期的档案数据集被用来确定悬崖底部侵蚀及其通过悬崖剖面向上传播的阈值。此外，“GEO-Slope”动态耦合水文稳定性模型用于建立降雨输入变化驱动的悬崖面失效阈值。后退机制是复杂的，由悬崖地质，既作为一个主要的控制吸力损失，并通过其与基础海洋条件的相互作用。这项研究允许悬崖撤退的软岩悬崖的一般模型，提出了一个抵抗的基础平台上覆盖着更易受侵蚀，弱和中等胶结的砂和砾石。在这个模式中，海洋和陆地强迫因子之间的不同平衡反映在低（<4 ma −1）、中等（4- 7 ma −1）和高（> 7 ma −1）的悬崖后退模式中。
Understanding changing thresholds and mechanisms for retreat in soft rock cliffs is important under changing climates. This can be achieved through combining detailed field observation, long-term process and morphological monitoring and numerical modelling. The cliffs of the Suffolk coast, southern North Sea have exhibited long-term (1883–2010) recession rates of 3.5ma−1, rising to 4.7ma−1in the period 1993–2010. Annual to biannual ground survey data, and the application of GIS techniques to digitised records of changing shoreline position from historic maps and aerial photography, reveal considerable decadal-scale variations in cliff recession, within which are nested inter-annual fluctuations in rates of retreat. Archival datasets on significant periods of onshore winds and their interaction with high water levels (including the incidence of storm surges) and rainstorm events are used to determine thresholds for cliff base erosion and its propagation upwards through the cliff profile. In addition, the ‘GEO-Slope’ dynamic coupled hydrology-stability model is used to establish thresholds for cliff face failures driven by variations in rainfall inputs. Retreat mechanisms are complex, governed by cliff geology, both as a primary control on suction loss and through its interaction with basal marine conditions. The study allows a general model of cliff retreat for soft rock cliffs to be put forward, whereby a resistant basal platform is overlain by more erodible, weakly and moderately cemented sands and gravels. In this model, the varying balance between marine and terrestrial forcing factors are reflected in low (<4ma−1), intermediate (4–7ma−1) and high (>7ma−1) modes of cliff retreat.