In situ cone penetration tests at the active Dashgil mud volcano,Azerbaijan: Evidence for excess fluid pressure,updoming, and possible future violent eruption |
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| Authors: | Achim Kopf Sylvia Stegmann Georg Delisle Behrouz Panahi Chingiz S Aliyev Ibrahim Guliyev |
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| Institution: | 1. MARUM Research Centre, University of Bremen, Leobener Strasse, Marum Building, 28359 Bremen, Germany;2. Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30561 Hannover, Germany;3. Geological Institute, Azerbaijan National Academy of Sciences, H. David Avenue 29A, 370143 Baku, Azerbaijan |
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| Abstract: | Active mud volcanism is a global phenomenon that represents a natural hazard by self-igniting eruptions and the continuous emission of methane gas in both marine and continental settings. Mud domes are often found in compressional tectonic settings such as the Caucasus orogenic wedge. Dashgil mud volcano, the most prominent of >200 features in Azerbaijan, has erupted vigorously in historic times. For several years, we have observed variations in the activity of Dashgil dome, including transients in methane flux, build-up of extrusive mud cones on the main feature, and flexural polygonal cracks adjacent to the main crater lake and new mud cones. In spring 2007, we carried out in situ CPTU (Cone Penetration Testing with Pore Pressure measurement) experiments in the crestal area of Dashgil. Our data suggest that the central portion of the crater lake, which hosts the conduit for gas (and possible mud) ascent, shows both low sediment shear strength (<5–20 kPa) and excess pore fluid pressures between 15 and 30 kPa supra-hydrostatic at 1 m sub-bottom depth. In situ cone resistance as a measure for undrained shear strength is as low as 150 kPa in the conduit, whereas the mud is found rather stiff in all other testing locations (300–700 kPa, probably a result of deeply buried shales of the Maikop formation parts of which now liquefy and ascend). Pore pressure is low in the centre of the conduit, probably because of rapidly migrating gas. It increases to 30 kPa at the lake bottom and deep flank, then decreases upslope on the lake flank, and reaches hydrostatic values at the crater rim. From the overpressured region beneath the fluid-filled crest of Dashgil dome, combined with the other observations, we suspect to currently witness an ongoing period of updoming. The presence of sintered mudstones from explosive eruptions in 1908 and 1928 (and most likely before) suggests that a similar violent activity may occur in the near future. |
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| Keywords: | Mud volcanism Cone penetration testing Shear strength Pore pressure Methane emission |
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