Abstract
A key factor limiting our understanding of rock slope behavior and associated geohazards is the interaction between internal and external system controls on the nature, rates, and timing of rockfall activity. We use high-resolution, monthly terrestrial light detection and ranging (LiDAR) surveys over a 2 year monitoring period to quantify rockfall patterns across a 0.6 km-long (15.3 × 103 m2) section of a limestone rock cliff on the northeast coast of England, where uncertainty in rates of change threaten the effective planning and operational management of a key coastal cliff top road. Internal system controls, such as cliff material characteristics and foreshore geometry, dictate rockfall characteristics and background patterns of activity and demonstrate that layer-specific analyses of rockfall inventories and sequencing patterns are essential to better understand the timing and nature of rockfall risks. The influence of external environmental controls, notably storm activity, is also evaluated, and increased storminess corresponds to detectable rises in both total and mean rockfall volume and the volumetric contribution of large (>10 m3) rockfalls at the cliff top during these periods. Transient convergence of the cumulative magnitude–frequency power law scaling exponent (ɑ) during high magnitude events signals a uniform erosion response across the wider cliff system that applies to all lithologies. The tracking of rockfall distribution metrics from repeat terrestrial LiDAR in this way demonstrably improves the ability to identify, monitor, and forecast short-term variations in rockfall hazards, and, as such, provides a powerful new approach for mitigating the threats and impacts of coastal erosion.
Highlights
Rockfall, or the removal of individual and superficial rocks from a cliff face [1,2], is a significant geohazard, on coastal cliffs where the exposure of people and assets is often high [3,4]
Recent work by Esposito et al [31] utilized repeat terrestrial light detection and ranging (LiDAR) and change detection methods to quantify recession of a ~1 km-long volcaniclastic sea cliff in southern Italy over a 3 year survey interval. They found that most rockfall event volumes that were detected at this spatiotemporal resolution were between 0.01 and 1 m3 and that a seawall structure was effective at reducing erosion driven directly by marine action at the cliff toe, demonstrating the utility of LiDAR-based studies for evaluating the efficacy of coastal defense engineering
We have presented an analysis of a rockfall inventory acquired through high-resolution topographic change detection applied to a section of limestone coastal rocky cliff in northeast England
Summary
The removal of individual and superficial rocks from a cliff face [1,2], is a significant geohazard, on coastal cliffs where the exposure of people and assets is often high [3,4]. Recent work by Esposito et al [31] utilized repeat terrestrial LiDAR and change detection methods to quantify recession of a ~1 km-long volcaniclastic sea cliff in southern Italy over a 3 year survey interval. They found that most rockfall event volumes that were detected at this spatiotemporal resolution were between 0.01 and 1 m3 and that a seawall structure was effective at reducing erosion driven directly by marine action at the cliff toe, demonstrating the utility of LiDAR-based studies for evaluating the efficacy of coastal defense engineering. To overcome the spatial constrictions of ground-based LiDAR, Benjamin et al [32] utilized annual helicopter-based LiDAR and change detection methods to detect rockfall activity across a regional (20.5 km) spatial scale for coastal cliffs along the North Yorkshire coast, England, and found that variations in rockfall shape with volume could provide insights into the underlying mechanisms of detachment with scale, and that the role of cliff retreat via large and infrequent (or ‘episodic’) failure can be significant for rocky coastlines, in contrast with the commonly held view that these landscapes are relatively stable
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