Recent unrest at Campi Flegrei caldera: New signatures and comparison with previous large unrest episodes (1969-1984)

English Abstract:

Campi Flegrei caldera, in the Neaples area which is marked by the highest volcanic risk in the world, has experienced, in the last 2000 years, up and down ground movements spanning about 20 m. The largest recent unrest episodes involving huge uplift (up to 3.5 m in 15 years) occurred since 1969 to 1984, but modern uplift episodes likely started in the 50’s of the last century. Following the spectacular ground uplift culminated in 1984 (uplift rates up to 1m/year) about 20 years of general subsidence started, interbedded with some small uplift episodes (4-11 cm of maximum elevation) lasting 1-2 months. Such subsidence period ended at about 2004, when a general trend of slow uplift started, with peak rates in 2006, 2012, 2013 and 2014. Since 2011, maximum ground uplift measured at Pozzuoli Bay has been 21 cm. The new slow uplift phase has characters different from the 1969-1972 and 1982-1984 large unrests, because uplift rates are much lower (about two orders of magnitude) and seismicity is much weaker, both in frequency and magnitude of the events. However, geochemical signatures of the on-going unrest are more marked than in previous periods, because a linearly increasing trend of huge deep fluid injection into shallow aquifers is evident from ground emissions. The ‘deep’ (or magmatic) signature of such injected fluids is even higher than during the previous largest unrests. These contrasting characters of the new unrest phase, when compared with the large unrests experienced 30-45 years ago, call for detailed interpretations of these episodes to discriminate magmatic from deep geothermal effects. This work presents the observational evidences of these peculiar unrest episodes and provides a first attempt to discriminate between magma accumulation effects and deep geothermal fluids injection. Such interpretation, based on thermal-fluid-dynamical modelling, relies on accurate in-situ estimation of permeability at depth operated in the framework of the ICDP-CFDDP (Campi Flegrei Deep Drilling Project).