Long-term in situ monitoring at Dashgil mud volcano, Azerbaijan: a link between seismicity, pore-pressure transients and methane emission

Abstract

Mud volcanism is a global phenomenon usually associated with compressional tectonics that favour extrusion of fluid-and clay mineral-rich sediment both on land and offshore. Methane, the dominant gas phase, is emitted at variable rates during and after emplacement of the mud domes. In case of continental mud volcanoes, the gas is directly released into the atmosphere, thereby contributing to global warming. Azerbaijan is one of the countries with one of the highest abundances of mud domes globally. One of the most prominent mud volcanoes, Dashgil, has been chosen for a case study because of its historic record of violent eruptions, continued activity, and well-documented regional geology in the Caucasus orogenic wedge adjacent to the Caspian Sea. Since 2003, gas flux has quantitatively measured at one of the two crater lakes and is characterized by valve-type behaviour and episodically violent degassing. In 2007, the large crater lake was additionally equipped with methane fluxmeters as well as an in situ pore-pressure probe into the conduit. Our data are complemented by regional seismicity, and exhibit the following results: (1) there seems to be a significant correlation between changes in pore pressure in the conduit feeding the main crater lake and the rate of gas escape; (2) changes in gas-flux rate appear to be independent of local seismicity, in particular since no larger EQs have been recorded since 2003; (3) despite discontinuous monitoring owing to technical failures, we observe an overall increase in methane emission with time; (4) nearby earthquake activity (\M4.6) can be correlated with pore-pressure transients recorded by the piezometer, which reach up to 2.4 kPa compared to the pre-seismic value; (5) from time to time, there are strong lake-level fluctuations decoupled from precipitation or evaporation, which are explained by subbottom hydraulic communication between the two crater lakes and adjacent gryphons. The wealth of observations leads us to conclude that monitoring gas flux and pore pressure provides important time series data for both methane emission into the atmosphere and pore pressure as a proxy for co-seismic strain.

Monitoring methane emission of mud volcanoes by seismic tremor measurements: a pilot study

“…also exist which make this kind of measurements infeasible and expensive in many contexts (Kopf et al, 2010). These difficulties explain also why most estimates of gas outflow from inland mud volcanoes are only performed by spot measurements (e.g.…”

“…1). The bulk of Dashgil is formed by clayed mud with variable amounts of clasts in the matrix originating from the Maikop formation at several kilometres depth (Kopf et al, 2010). Dashgil volcano is one of the most active mud domes of the Earth, and the last major eruptions occurred in the years 1882, 1902, 1908, 1926and 1958(e.g.…”

“…Beyond this paroxystic activity, it also represents a good example of mud volcano with high seep activity in the dormant period (Planke et al, 2003). Due to these features, Dashgil volcano has been extensively studied in the past from the geomorphologicalgeostructural (Hovland et al, 1997;Roberts et al, 2011), geochemical (Planke et al, 2003), and geotechnical (Kopf et al, 2009) point of view and was the object of long-term monitoring of gaseous emissions (mainly Methane) at the summit area (Kopf et al, 2010).…”

“…Such monitoring is also of interest for hazard assessment in many countries where dramatic inland mud eruptions have been historically documented (see, e.g. Aliyev et al, 2009; and as a proxy for co-seismic strain detection (Albarello, 2005;Kopf et al, 2010;.…”

“…In principle, monitoring the activity of mud volcanoes in terms of gas outflow is possible by capturing emissions at the surface of emitting conduits (Kopf et al, 2010;Martinelli et al, 1995). However, as this approach works well when small structures are of concern, when several independent seepage structures and diffuse microseepage exist (e.g.…”