Analogue models are commonly used to gain insights into large-scale volcano-tectonic processes. Documenting model surface topography and the three-dimensional (3D) aspect of deformation structures remains the greatest challenge in understanding the simulated processes. Here we present the results of volcano analogue models imaged with an X-ray computerized micro-tomography (μCT) system developed at the Ghent University Centre for Tomography (UGCT). Experiments simulate volcano deformation due to gravitational loading over a ductile layer, a process affecting many natural volcanoes built over a sedimentary substratum. Results show that μCT is able to provide a 3D reconstruction of the model topography with unprecedented resolution. Virtual cross sections through reconstructed models enable us to map the main structures at depth and to document the deformation of the brittle-ductile interface due to contrasting X-ray attenuation. Results for lateral spreading and vertical sagging into thin and thick ductile layers, respectively, are illustrated for circular cones and elongated ridges. Results highlight structural patterns not seen in previous models, such as: 1) the 3D form of a polygonal brecciated zone at the center of spreading cones; 2) the complete lack of such a zone in sagging cones; and 3) relay structures between graben-bounding faults in spreading cones. In addition, detailed imaging of tension gashes and of the flexure surface below sagging cones enables the 3D strain distribution to be explored. Experiments with non-cohesive and low cohesion granular materials present striking differences in surface topography and fault characteristics. Despite limitations associated with the scan duration, μCT reconstruction of analogue models appears a powerful tool for better understanding the complex 3D deformation associated with volcano-tectonic processes.
Abstract X-ray computed tomography (CT) is a non-destructive technique with wide applications in various geological disciplines. It reveals the internal structure of objects, determined by variations in density and atomic composition. Large numbers of parallel 2D sections can be obtained, which allows 3D imaging of selected features. Important applications are the study of porosity and fluid flow, applied to investigations in the fields of petroleum geology, rock mechanics and soil science. Expected future developments include the combined use of CT systems with different resolutions, the wider use of related X-ray techniques and the integration of CT data with results of compatible non-destructive techniques.
High spatial resolution topographic data are crucial as a prerequisite for evaluating and modelling volcanic hazards. Remote sensing now provides some of the best methods of retrieving digital elevation models (DEMs) over extensive volcanic regions. Here we compare the advantages and limitations of Shuttle Radar Topography Mission (SRTM) DEMs, derived from radar interferometry, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEMs, derived from digital photogrammetry. Applications are presented for Mauna Kea (MK), Hawaii and Oldoinyo Lengai (OL), Tanzania. We quantitatively assess the accuracy of the respective DEMs to document the size of moderate‐sized volcanic features. ASTER DEM accuracy depends on spectral contrast within the image and on the availability of high‐quality ground control points. Unlike the ASTER DEMs, which are user‐derived, processed SRTM DEMs are provided without estimations of the vertical accuracy for each scene, and the end‐user has no control over the processing method. From comparison with a 10‐m spatial resolution DEM derived from 1 : 24 000 scale topographic maps of MK, we estimate root mean square errors at 8, 10 and 13 m for SRTM 30‐m, SRTM 90‐m and ASTER 30‐m DEMs, respectively. For scoria cones (<200 m high, <2 km basal diameter), SRTM 30‐m, SRTM 90‐m and ASTER 30‐m DEMs underestimate cone height by 9.5, 27 and 14%, respectively, mostly because of the averaging effect of decreasing spatial resolution. For height estimations of volcanic features higher than ∼100 m in the OL region, all of the DEMs tested were found to be consistent.
Many rock types are formed under high temperature and/or high pressure conditions in the upper part of the earth's crust. In order to evaluate rocks used as building material, several characterization tests (petrographic analysis, determination of the porosity, pressure resistance, etc.) and durability tests (freeze-thaw resistance, thermal shock resistance, etc.) exist. The main shortcomings in these traditional durability tests are that these evaluations are mainly based on visual inspection and that there is no quantification of internal micro-structural reorganization. Internal quantification of dynamic processes still remains difficult with destructive analysis tools. For that purpose, in this chapter non-destructive high resolution x-ray computed tomography (CT) is combined with image analysis to visualize, characterize and quantify freeze-thaw cycles of the Noyant Fine limestone and pressure test on the Euville, Noyant Fine and Savonnières limestone. Controlled Vocabulary Terms building materials; computerised tomography
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