Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño
Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño
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DOI：
10.1016/s0025-3227(02)00316-x
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发表时间：
2002-07
期刊：
影响因子：
2.9
通讯作者：
A. Sallenger;W. Krabill;J. Brock;R. Swift;S. Manizade;H. Stockdon
中科院分区：
文献类型：
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作者：
A. Sallenger;W. Krabill;J. Brock;R. Swift;S. Manizade;H. Stockdon
在数百年至数千年的时间尺度上，沿着加利福尼亚中部海岸的净沿岸沙输送方向已被北太平洋冬季海浪驱使至南部。相比之下，在 1997 年至 1998 年的厄尔尼诺冬季，机载激光雷达测量前后的比较显示，沙子从南向北输送，并堆积在与小型海滩接壤的抵抗海岬的南侧。这导致了袖珍海滩南端的严重海滩侵蚀和北端的沉积。与沙子从南向北重新分布的同时，海岸线形态变得明显尖状，长岸波长为 400-700 m。海滩的宽度和高度最小，海岸线侵蚀最严重，悬崖优先暴露于海浪的攻击下。由此产生的侵蚀热点通常位于袖珍海滩南端的巨大尖头海湾。观测到的海崖退缩幅度达到 14 m，随极端波浪上升超过特定阈值的小时数而变化，这代表了厄尔尼诺冬季海滩的保护能力。表示海滩宽度的阈值比表示海滩高度的阈值表现更好。悬崖侵蚀的程度可以使用一个简单的模型来衡量，该模型基于极端波浪上升超过冬季前悬崖位置的跨岸距离。悬崖侵蚀似乎是陆地质量消耗过程和波浪攻击之间的平衡，前者会降低悬崖坡度，后者会清除碎片并侵蚀悬崖底部，从而增加悬崖坡度。
Over time scales of hundreds to thousands of years, the net longshore sand transport direction along the central California coast has been driven to the south by North Pacific winter swell. In contrast, during the El Niño winter of 1997–1998, comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches. This resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends. Coincident with the south-to-north redistribution of sand, shoreline morphology became prominently cuspate with longshore wavelengths of 400–700 m. The width and elevation of beaches were least where maximum shoreline erosion occurred, preferentially exposing cliffs to wave attack. The resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches. The observed magnitude of sea cliff retreat, which reached 14 m, varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the El Niño winter. A threshold representing the width of the beach performed better than a threshold representing the elevation of the beach. The magnitude of cliff erosion can be scaled using a simple model based on the cross-shore distance that extreme wave runup exceeded the pre-winter cliff position. Cliff erosion appears to be a balance between terrestrial mass wasting processes, which tend to decrease the cliff slope, and wave attack, which removes debris and erodes the cliff base increasing the cliff slope.