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High-resolution three-dimensional imaging and analysis of rock falls in Yosemite Valley, California

机译：加利福尼亚州优胜美地谷的高分辨率三维成像和岩石瀑布分析

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We present quantitative analyses of recent large rock falls in Yosemite Valley, California, using integrated high-resolution imaging techniques. Rock falls commonly occur from the glacially sculpted granitic walls of Yosemite Valley, modifying this iconic landscape but also posing significant potential hazards and risks. Two large rock falls occurred from the cliff beneath Glacier Point in eastern Yosemite Valley on 7 and 8 October 2008, causing minor injuries and damaging structures in a developed area. We used a combination of gigapixel photography, airborne laser scanning (ALS) data, and ground-based terrestrial laser scanning (TLS) data to characterize the rock-fall detachment surface and adjacent cliff area, quantify the rock-fall volume, evaluate the geologic structure that contributed to failure, and assess the likely failure mode. We merged the ALS and TLS data to resolve the complex, vertical to overhanging topography of the Glacier Point area in three dimensions, and integrated these data with gigapixel photographs to fully image the cliff face in high resolution. Three-dimensional analysis of repeat TLS data reveals that the cumulative failure consisted of a near-planar rock slab with a maximum length of 69.0 m, a mean thickness of 2.1 m, a detachment surface area of 2750 m2, and a volume of 5663 ?± 36 m3. Failure occurred along a surface-parallel, vertically oriented sheeting joint in a clear example of granitic exfoliation. Stress concentration at crack tips likely propagated fractures through the partially attached slab, leading to failure. Our results demonstrate the utility of high-resolution imaging techniques for quantifying far-range (1 km) rock falls occurring from the largely inaccessible, vertical rock faces of Yosemite Valley, and for providing highly accurate and precise data needed for rock-fall hazard assessment.
机译：我们使用集成的高分辨率成像技术呈现近期大型岩石瀑布的定量分析。岩石瀑布通常发生在优胜美地谷的羽毛雕刻的花岗岩墙壁，改变这种标志性景观，但也构成了显着的潜在危险和风险。 2008年10月7日和8日，东部优胜美地谷的冰川点下的冰川点下面发生了两大岩石瀑布，在发达地区造成轻微伤害和破坏性结构。我们使用了千兆像素摄影，空中激光扫描（ALS）数据和地面陆地激光扫描（TLS）数据的组合，以表征岩石脱落脱落表面和相邻的悬崖面积，量化摇滚落体，评价地质有助于失败的结构，并评估可能的失效模式。我们合并了ALS和TLS数据以解决复杂的复杂，垂直于三维冰川点区域的悬垂地形，并将这些数据与Gigapixel照片集成在一起以在高分辨率中完全映像悬崖面。重复TLS数据的三维分析表明，累积故障由近平面岩石板组成，最大长度为69.0米，平均厚度为2.1μm，脱离表面积为2750m 2，体积为5663° ±36 m3。在花岗岩剥离的透明实例中，沿着表面平行的垂直定向片接头发生故障。裂缝提示处的应力浓度可能通过部分附着的板坯传播骨折，导致失败。我们的结果展示了用于量化远程（＆ 1 km）岩石的高分辨率成像技术的效用，从优胜美地谷的主要难以接近的垂直岩面发生，以及为岩石落下提供高度准确和精确的数据危险评估。

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