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Baran, Ramona (2012): Quantification of landscape evolution on multiple time-scales: applications of high-resolution 3-D laser scanning and erosion measurements to tectonic and geomorphological questions. Dissertation, LMU München: Faculty of Geosciences
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Abstract

Essential information about the activity or even the mechanics of tectonic and erosional processes can be extracted from their surface expression. For this purpose, it is necessary to appropriately constrain the temporal as well as the spatial framework, in which to consider a specific process. While recently developed dating techniques, such as thermochronology or radiocarbon dating, allow to assess the age of landforms and therefore rates of tectonic and erosional processes, detailed spatial information is also required to assess these rates correctly. Due to a lack of appropriate topographic data in the past it was sometimes challenging to reliably approximate the spatial framework, because the size of a particular landform can often cover a wide range of spatial scales. Recently available, conventional topographic data, such as those of the Shuttle Radar Topography Mission, substantially improved the definition of an appropriate spatial framework due to their spatial coverage and resolution of down to less than 1 m. However, to constrain this framework at a detail beyond the resolution of several decimeter terrestrial laser scanning provides a highly efficient approach. This technique permits the rapid acquisition (within minutes) of tremendous amounts of topographic data with both, a high resolution of a few centimeters and a high accuracy of a few millimeters. High-resolution topographic maps of a certain area of the surface of the Earth are derived from individual laser-scanner measurements, that in turn allow to characterize the in-situ geomorphic setting at great detail. Moreover, repeated measurements of this area allow to quantify morphological changes thereby supporting the survey of surface processes on short-term scales ranging from days up to several years. The former approach is best suited for tectono- and the latter one for fluvial-geomorphic studies, and we present results from two case studies that are either based on single or repeated laser-scanner measurements. In the first case, we combined field mapping and high-resolution digital elevation model (DEM) analysis to evaluate the detailed meter- to hundred meter-scale structure and surface expression of one flank of the Rex Hills pressure ridge in the western United States. Based on terrestrial laser scanning (Riegl LMS-Z420i) we derived a DEM with cm-scale resolution and extracted high-resolution topographic cross-sections. This enabled us to identify fault scarps and determine their relative ages and geometry. In the second case, we carried out a detailed field mapping of erosion and sedimentation patterns in the Alp Valley, central Switzerland, to assess its Holocene evolution. Simultaneously, we conducted repeated high-resolution (less than 1 cm locally) laser-scanning surveys (Topcon TLS-1000) along two tributaries, the Erlenbach and Vogelbach, to determine channel-morphology changes and the nature of shortest-term sediment transport by comparing the individual DEMs derived from these measurements, as well as to evaluate the context to the longer-term evolution of the Alp Valley. Both case studies, however, highlight the potential of medium-range laser scanners with measurement distances of up to hundreds of meters. Such scanners are most appropriate to efficiently analyze closely-spaced fault scarps across a broad range of spatial scales, and to document complex morphologic changes in small mountainous torrents due to sediment transport. Moreover, terrestrial laser scanning is a key tool to monitor surface processes, but the insights gained from this method are generally evaluated best in the context of further data sets including geochronological, structural, subsurface, or climate data. Surface processes, in particular erosion, sediment transport, and deposition in sedimentary basins are intermittent in space and time challenging both, the appropriate definition of a spatiotemporal framework addressed above and a comprehensive process understanding. A major objective of this thesis is to contribute to a better understanding of scale linkage concerning these processes. We therefore first carried out a comprehensive comparison of short- to long-term erosion measurements from the Alps based on an approach originally established to evaluate the significance of geologic and geodetic measurements along intra-continental faults on time scales of millions to tens of years. In a second step, we re-assessed the sediment budget of the Alps, a data set that is usually considered to be an appropriate measure of long-term erosion in the Alps. The two major results of both studies indicate that: short- and medium-term erosion in the Alps over years to ten thousands of years is dominantly influenced by climate and weather variability, e.g., due to seasonal differences in the amount of precipitation; whereas long-term erosion over millions of years is controlled by tectonic processes.