Tsunamis and storms cause considerable coastal flooding, numerous fatalities, destruction of structures, and erosion. The characterization of energy and frequency associated with each wave contribute to the risk assessment in coastal regions. Coastal boulder deposits represent a physical proof of extreme inundation and allow us to study the effects of marine floods further back in time than instrumental and historical records. Age estimation of these deposits is challenging due to lack of materials (such as sand, shells, corals, or organic matter) that retain information about the passage of time. Lichenometry, a simple age estimation method, which is cost-effective, quick to apply, and non-destructive, is here proposed as a solution. A lichen growth model for a calcium-tolerant lichen species was developed and used to estimate the age of a boulder deposit related to extreme marine inundation(s) in Portugal. Estimated ages indicate several very recent events (<700 years) for most of the boulders’ stabilization and agree with results obtained with optically stimulated luminescence of marine sands found beneath boulders. Frequent and recent boulder transport implies a storm-origin for this deposit. These conclusions contrast with other works describing identical deposits that are attributed to paleotsunamis. This study presents a methodology using lichenometry as a successful alternative for age estimation in rocky coastal settings. These results offer an alternative explanation for coastal boulder deposits found on the west coast of Portugal.

中文翻译：

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使用地衣测量法估计与极端波浪有关的巨石运输的年龄和机制

海啸和风暴会导致严重的沿海洪水、无数人死亡、建筑物破坏和侵蚀。与每个波浪相关的能量和频率的特征有助于沿海地区的风险评估。沿海巨石沉积物代表了极端淹没的物理证据，使我们能够比仪器和历史记录更早地研究海洋洪水的影响。由于缺乏能够保留时间流逝信息的材料（例如沙子、贝壳、珊瑚或有机物），因此对这些沉积物的年龄估计具有挑战性。地衣测量法是一种简单的年龄估计方法，具有成本效益、应用迅速且无损，这里提出作为解决方案。开发了一种耐钙地衣物种的地衣生长模型，并用于估计与葡萄牙极端海洋淹没相关的巨石沉积物的年龄。估计的年龄表明大多数巨石稳定的几个非常近期的事件（<700 年），并且与在巨石下发现的海砂的光学刺激发光所获得的结果一致。频繁和最近的巨石运输意味着该矿床的风暴起源。这些结论与描述归因于古海啸的相同沉积物的其他著作形成对比。这项研究提出了一种使用地衣测量法作为岩石海岸环境中年龄估计的成功替代方法的方法。这些结果为葡萄牙西海岸发现的沿海巨石沉积提供了另一种解释。