Small landslides in the upper submarine slopes of volcanic islands present potential hazards locally because of their high frequency. We examine evidence for landsliding in high-resolution bathymetric data from Faial, Pico, São Jorge, and Terceira islands of the Azores. Because the rugged morphology of the upper slopes makes landslides difficult to interpret, we develop two classification schemes for the 1,227 identified slope valleys. One scheme addresses how recognizable the valleys were as originating from landslides (whether scarps are prominent or indefinite), whereas the other scheme addresses valley types (whether apparently produced by single or multiple failures). Size distributions are used to assess the relative occurrence of large versus small landslides. Thirteen landslides are predicted to have generated tsunami heights at source of >1 m and one with height of >7 m. Some slopes have gradients far above 30°, the angle of repose of incohesive clastic sediment, so the seabed in those areas is strengthened perhaps by carbonate cementation, by seismic shaking or by the presence of coherent lava or lava talus. Using all types of slope valleys, Faial and Pico have smaller affected volumes per unit slope area than those of São Jorge and Terceira. These differences could be associated with varied seismic activity, with more frequent earthquakes beneath Faial and Pico preventing the build-up of sediments on their slopes. Submarine landslide statistics are therefore potentially useful for assessing long-term earthquake hazards of volcanic islands in seismically active environments such as the Azores.

中文翻译：

---

火山岛上层海底斜坡的滑坡：中亚速尔群岛

火山岛上部海底斜坡的小型滑坡由于其频率高，在局部存在潜在危害。我们检查了来自亚速尔群岛 Faial、Pico、São Jorge 和 Terceira 群岛的高分辨率水深数据中的滑坡证据。由于上坡崎岖的形态使滑坡难以解释，我们为 1,227 个已识别的坡谷制定了两种分类方案。一个方案解决了山谷起源于山体滑坡的可识别性（陡坡是突出的还是不确定的），而另一个方案则解决了山谷类型（显然是由单个或多个故障产生的）。大小分布用于评估大滑坡与小滑坡的相对发生率。预计 13 次山体滑坡在震源处产生海啸高度 >1 m 和 1 次超过 7 m。一些斜坡的坡度远高于 30°，即非粘性碎屑沉积物的休止角，因此这些地区的海床可能通过碳酸盐胶结、地震震动或连贯熔岩或熔岩距骨的存在而得到加强。使用所有类型的坡谷，Faial 和 Pico 的单位坡面积受影响体积小于 São Jorge 和 Terceira。这些差异可能与不同的地震活动有关，Faial 和 Pico 下方更频繁的地震阻止了沉积物在其斜坡上的堆积。因此，海底滑坡统计数据对于评估亚速尔群岛等地震活跃环境中火山岛的长期地震危害可能有用。