The measurement of topography and of topographic change is essential for the study of many geomorphic processes. In recent years, structure from motion (SfM) techniques applied to photographs taken ...by camera-equipped unmanned aerial vehicles (UAVs) has become a powerful new tool for the generation of high resolution topography. The variety of available UAV systems continues to increase rapidly, but it is not clear whether increased UAV sophistication translates into improved quality of the calculated topography. To evaluate the lower end of the UAV spectrum, a simple low cost UAV was deployed to calculate high resolution topography in the Daan River gorge in western Taiwan, a site with a complicated 3D morphology and a wide range of surface types, making it a challenging site for topographic measurement. Terrestrial lidar surveys were conducted in parallel with UAV surveys in both June and November 2014, enabling an assessment of the reliability of the UAV survey to detect geomorphic changes in the range of 30cm to several meters. A further UAV survey was conducted in June 2015 in order to quantify changes resulting from the 2015 spring monsoon. To evaluate the accuracy of the UAV derived topography, it was compared to terrestrial lidar data collected during the same survey period using the cloud-to-cloud comparison algorithm M3C2. The UAV-generated point clouds match the lidar point clouds well, with RMS errors of 30–40cm; however, the accuracy of the SfM point clouds depends strongly on the characteristics of the surface being considered, with vegetation, water, and small scale texture causing inaccuracies. The lidar and SfM data yield similar maps of change from June to November 2014, with the same areas of geomorphic change detected by both methods. The SfM-generated change map for November 2014 to June 2015 indicates that the 2015 spring monsoon caused erosion throughout the gorge and highlights the importance of event-driven erosion in the Daan River. The results suggest that even very basic UAVs can yield data suitable for measuring geomorphic change on the scale of a channel reach.
•Comparison of repeat lidar and low cost UAV-derived point clouds of a bedrock gorge•Repeat UAV surveys can reliably detect changes greater than ~30cm on the reach scale.•Erosion in the Daan River is controlled by storm size rather than total precipitation.
Himalayan rivers are frequently hit by catastrophic floods that are caused by the failure of glacial lake and landslide dams; however, the dynamics and long-term impacts of such floods remain poorly ...understood. We present a comprehensive set of observations that capture the July 2016 glacial lake outburst flood (GLOF) in the Bhotekoshi/Sunkoshi River of Nepal. Seismic records of the flood provide new insights into GLOF mechanics and their ability to mobilize large boulders that otherwise prevent channel erosion. Because of this boulder mobilization, GLOF impacts far exceed those of the annual summer monsoon, and GLOFs may dominate fluvial erosion and channel-hillslope coupling many tens of kilometers downstream of glaciated areas. Long-term valley evolution in these regions may therefore be driven by GLOF frequency and magnitude, rather than by precipitation.
Seismic Advances in Process Geomorphology Cook, Kristen L; Dietze, Michael
Annual review of earth and planetary sciences,
05/2022, Letnik:
50, Številka:
1
Journal Article
Recenzirano
Odprti dostop
One of the pillars of geomorphology is the study of geomorphic processes and their drivers, dynamics, and impacts. Like all activity that transfers energy to Earth's surface, a wide range of ...geomorphic process types create seismic waves that can be measured with standard seismic instruments. Seismic signals provide continuous high-resolution coverage with a spatial footprint that can vary from local to global, and in recent years, efforts to exploit these signals for information about surface processes have increased dramatically, coalescing into the emerging field of environmental seismology. The application of seismic methods has the potential to drive advances in our understanding of the occurrence, timing, and triggering of geomorphic events, the dynamics of geomorphic processes, fluvial bedload transport, and integrative geomorphic system monitoring. As new seismic applications move from development to proof of concept to routine application, integration between geomorphologists and seismologists is key for continued progress.
Geomorphic activity on Earth's surface produces seismic signals that can be measured with standard seismic instruments.
Seismic methods are driving advances in our understanding of the occurrence, triggering, and internal dynamics of a range of geomorphic processes.
Dedicated seismic-based observatories offer the potential to comprehensively characterize geomorphic activity and its impacts across a landscape.
Collaboration between seismologists and geomorphologists is fostering the development of new applications, models, and analysis techniques for geomorphic seismology.
High-quality 3-D point clouds generated from repeat camera-equipped
unmanned aerial vehicle (UAV) surveys are increasingly being used to
investigate landscape changes and geomorphic processes. Point ...cloud quality
can be expressed as accuracy in a comparative (i.e., from survey to survey)
and absolute (between survey and an external reference system) sense. Here
we present a simple workflow for calculating pairs or sets of point clouds
with a high comparative accuracy, without the need for ground control points
or a differential GNSS (dGNSS)-equipped UAV. The method is based on the automated detection of
common tie points in stable portions of the survey area. We demonstrate the
efficacy of the new approach using a consumer-grade UAV in two contrasting
landscapes: the coastal cliffs on the island of Rügen, Germany, and the
tectonically active Daan River gorge in Taiwan. Compared to a standard
approach using ground control points, our workflow results in a nearly
identical distribution of measured changes. Compared to a standard approach
without ground control, our workflow reduces the level of change detection
from several meters to 10–15 cm. This approach enables robust change
detection using UAVs in settings where ground control is not feasible.
The Tibetan Plateau is the type example of a large orogenic plateau formed as a result of continent‐continent collision. The morphology of the plateau and its margins suggests that preexisting ...variations in crustal strength have influenced the growth of the plateau. We have developed a three‐dimensional numerical model of deformation in a viscous crust in order to investigate the effects of lateral heterogeneities on plateau growth. The model includes a two layer crust and allows for lateral variation of viscosity in both the upper and lower layers. Model results indicate that crustal strength variations have a dramatic effect on the morphology and dynamics of a developing plateau. A region of strong crust is characterized by a very steep plateau margin that propagates extremely slowly, does not accommodate significant shortening strain, and is subparallel to local upper and lower crustal velocities. A weak crustal region develops a gently sloping margin; uplift propagates rapidly across the weak zone, and crustal material within the plateau is diverted toward the low‐strength region. With a relatively simple distribution of strength variations, corresponding to strong Tarim and Sichuan Basin crust and a weak southeastern corner, our model produces a plateau with many similarities to the Tibetan Plateau, including the overall morphology, rotation around the eastern syntaxis, and E–W extension. Analysis of model results suggests that E–W extension of the central plateau may be related to the rapid eastward flow of crustal material into a weak zone in the SE corner without significant change in plateau elevation.
Early warning is a critical potential tool for mitigating the impacts of large mass wasting and flood events, a major hazard in the Himalaya. We used data from a dense seismic network in Uttarakhand, ...India, to detect and track a fatal rockslide to mass flow to flood cascade and examine the potential for regional networks to provide early warning for extreme flow events. Detection limits of the 7 February 2021 event depend on the nature of the active process and on the anthropogenic and environmental seismic noise levels at each station. With the existing network, a seismic monitoring system could have detected all event phases from up to 100 kilometers and provided downstream warnings within minutes of event initiation.
Katherine Possin and colleagues report on the implementation, development, and early findings of the Care Ecosystem, an adaptive, personalized, and scalable dementia care program.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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