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Several remote sensing techniques, namely traditional aerial photographs, an unmanned aircraft system (UAS), and airborne lidar, were used in this study to decipher the morphological features of obscure landslides in volcanic regions and how the observed features may be used for understanding landslide occurrence and potential hazard. A morphological reconstruction method was proposed to assess landslide morphology based on the dome-shaped topography of the volcanic edifice and the nature of its morphological evolution. Two large-scale landslides in the Tatun volcano group in northern Taiwan were targeted to more accurately characterize the landslide morphology through airborne lidar and UAS-derived digital terrain models and images. With the proposed reconstruction method, the depleted volume of the two landslides was estimated to be at least 820±20x106 m³. Normal faulting in the region likely played a role in triggering the two landslides, because there are extensive geological and historical records of an active normal fault in this region. The subsequent geomorphological evolution of the two landslides is thus inferred to account for the observed morphological and tectonic features that are indicative of resulting in large and life-threatening landslides, as characterized using the recent remote sensing techniques. [ABSTRACT FROM AUTHOR]

Catastrophic landslides often cause serious disasters, and such incidents are often the focus of our attention. The well-known Tasoling Landslides occurred repeatedly, which were triggered by earthquakes, typhoons, and torrential rains in 1862, 1898, 1941, 1942, 1951, 1979, and 1999. Among these, the landslides in 1862, 1941, and 1999 were triggered by earthquakes. The Tsaoling area geologically belongs to a dip-slope terrain in interbedded Pliocene sandstone, mudstone, and shales. The volume of the rock debris accumulated from previous landslide events was about 0.026 - 0.126 km3, which formed a landslide dam with a height of 70-170 m and blocked the Qingshui river. The sudden failures of these landslide dams often resulted in additional catastrophes in the downstream areas, three of which occurred years after the landslide event. With the progress of surveying technology, high-resolution DEMs data could be used for important topics, such as landslides and geomorphic change. In this study, we presented multi-temporal remote sensing datasets for geomorphic changes in the Tsaoling landslide area before and after the Chichi earthquake and provided an effective DEM analysis technique to better estimate volume changes and surface movements. We found that multi-temporal data comparison could show the geomorphic changes of the Tsaoling landslide area directly at different times by using aerial photogrammetry and LiDAR DEM analysis. The observed results of geomorphic changes in the shorter period of 1- 3 years from 2011 to 2012, 2012 to 2016, 2016 to 2017 and over a long period time of about 9 years from 2002 to 2011, including the location of the landslide accumulation area, the change of cliff retreat, and the volume change of the debris after the landslide event. By means of terrain profile comparison, elevation change calculation and Particle image velocimetry (PIV) analysis from image and DEM data during 2016-2017, we found some surface displacement located in the lower half of the Tsaoling landslide area and distributed in the Chinshui shale area. Within the range of about 80 hectares, there was a clear trend of surface displacement, indicating that this range of the Tsaoling area may have slipped, which was similar to the scale as the 1942 landslide event. This study shows that the integrated use of aerial photogrammetry and LiDAR DEM data analysis method with multi-temporal topographic data collection and field surveys in the landslide area, and could resolve the surface changes and possible impacts of this large landslide and river geomorphological changes in the future. [ABSTRACT FROM AUTHOR]

The most commonly used 1:50,000 geological maps, which are generally in low resolution, provide only conceptual drawing for geological features. For advanced applications in science and engineering, the traditional geological maps no longer satisfy the requirements of precise 3D geological structures and accurate lithological distribution, particularly for engineering purposes. In order to solve the problem of insufficient accuracy of geological maps, we must apply a feasible set of techniques to further develop high-precision geological maps. Although various types of space measurement technology have made great progress in recent years, their application in producing geological maps is still seriously stagnant. This may be related to difficulty in obtaining comprehensive high-precision terrain models, lack of three-dimensional visual mapping environments, and especially failure to effectively develop techniques or modules needed to produce high-precision geological maps. In this study we used existing high-resolution LiDAR data and the latest computerized 3D environments to conduct and explore high-precision geological mapping. We developed computational modules for geological map production and explore various geological features in three dimensions for overcoming difficulties in traditional mapping. We mapped the terrain of the sedimentary rocks in the fold-and-thrust belt of western Taiwan, which contains typical strata from the Oligocene to Miocene. The study provides a new three-dimensional concept of geological mapping with a finished case example from the Shuanghsi quadrangle map in northern Taiwan. This research is expected to modify traditional geological mapping concepts and provides preliminary mapping techniques to enhance the foundation and strength of three-dimensional geological mapping for the future. [ABSTRACT FROM AUTHOR]