Campi Flegrei volcano (Italy): micro-seismic activity picks up

 

Another weak seismic swarm is in progress under Europe's most active caldera. Since yesterday, 12 weak earthquakes have occurred at shallow depths of mostly around 2 km under the ground since yesterday. None of these quakes was strong enough to be felt, but the very sensitive monitoring network of the Vesuvius volcano observatory of INGV (also responsible to monitor the Phlegrean Fields, and Ischia volcanoes) has detected an increase of micro-seismic activity already since October this year. In total, there have been 212 weak tremors in the area of ​​the caldera. 126 quakes of these occurred between Pozzuoli, the Solfatara-Pisciarelli area and the Gulf of Pozzuoli. Other parameters of volcanic unrest also remain above normal levels: Ground inflation is continuing slowly, but has totaled 87 cm uplift since 2005 in the most affected area near the Rione Terra GPS station. Gas emissions also continue to increase again, after having been on a decreasing trend in the previous months. This concerns especially carbon dioxide (CO2) diffusing through the ground, which is an early indicator of fresh magma arriving at depth, and measured in the area of the Pisciarelli fumaroles. Whether the current phase of unrest is sign of new magma accumulating and possibly getting ready for an eruption is far from certain. According to the scientists, the phenomena are likely part of the normal behavior of the caldera, which is characterized by so-called bradysism cycles - sustained periods of alternating slow ground up- and downlift. These are caused by gradual fluctuations or changes in temperature, composition and other geophysical properties of the very large and active hydrothermal system in the underground of the upper few kilometers. Such changes, e.g. temperature changes of the ground water and the contained gas bubbles in pores and rock fractures will make the ground "breathe" over long periods (years to centuries); imagine a dough with very active fermentation processes in its inside, will cause the crust to go up and down as gases are created, trapped and released, and the activity of fermentation changing with the temperatures it is exposed to.