2019 Cable Mountain Rockfall, Zion National Park, Utah

On August 24, 2019, at approximately 5:30 p.m., a large slab of Navajo Sandstone detached from a vertical cliff face of Cable Mountain above the Weeping Rock area, in Zion National Park, Utah. The slab of rock detached approximately 2000 vertical feet (610 meters) above the parking lot at the Weeping Rock trailhead. Utah Geological Survey (UGS) geologists conducted a site reconnaissance on August 26, 2019. An additional investigation including high-resolution photo-graphs and video collected using a small unmanned aircraft system (sUAS), was conducted October 24–25, 2019. Data were also collected to help assess the stability of a prolific rockfall area that has repeatedly damaged the nearby Hidden Canyon trail. The sUAS data collected were used to create a digital elevation model (DEM), structure from motion (Sf M) model, and an orthomosaic image of a large part of the western Cable Mountain, Weeping Rock, and Hidden Canyon areas. The estimated volume of the rock avalanche was calculated to be 435,712 cubic feet (12,338 m3). The rock mass was approximately 31,000 tons. The calculated volume and flow-like qualities of the event classify it as a very small rock avalanche. No specific triggering event could be identified for the rock avalanche event; however, it appears thermal cycling is a likely contributing factor. The recommended solution in this situation is (1) avoidance of the rockfall hazard, such as not building structures and limiting access in areas with frequent rockfall and/or (2) acceptance of the hazard and the risk associated with it, knowing that the consequences of this option could result in loss of life and damage to property.

2019年8月24日下午约5:30，一块巨大的纳瓦霍砂岩从犹他州锡安国家公园weeping rock区域上方Cable Mountain的垂直悬崖面上脱落。该岩石块脱落的高度约为2000英尺（约610米），位于weeping rock步道入口的停车场上方。犹他州地质调查局（Utah Geological Survey，简称UGS）的地质学家于2019年8月26日进行了现场勘查。2019年10月24日至25日，还进行了包括使用小型无人机系统（small unmanned aircraft system，简称sUAS）收集的高分辨率照片和视频在内的附加调查。收集的数据还用于评估一个反复损坏附近hidden canyon步道的多发岩石坠落区的稳定性。收集的sUAS数据被用于创建一个数字高程模型（digital elevation model，简称DEM）、运动结构模型（structure from motion，简称SfM）以及Cable Mountain西部、weeping rock和hidden canyon区域的大部分地区的正射影像图。根据计算，岩石雪崩的体积约为435,712立方英尺（约12,338立方米）。岩石体的质量约为31,000吨。根据事件的计算体积和流动特性，将其归类为非常小的岩石雪崩。无法确定岩石雪崩事件的特定触发事件；然而，热循环似乎是一个可能的促成因素。在这种情况下，建议的解决方案是：（1）避免岩石坠落危险，例如不在此类地区建造结构，并限制频繁岩石坠落区域的人流；（2）接受这种危险及其相关的风险，知道选择此方案可能导致人员伤亡和财产损失。