After the shock of earthquake of 30 October at 7.40 of magnitude M 6.5, mud emissions (volcanelli) have been detected in some localities in the province of Fermo. The geologists of EMERGEO, one of the seismic emergency operational groups of the National Institute of Geophysics and Volcanology (INGV), have taken steps to carry out preliminary investigations of this phenomenon which represents one of the secondary effects of earthquakes on the territory.
But what are mud volcanoes?
A little known but extremely widespread phenomenon in various parts of the Earth. Mud volcanoes are also present in Italy throughout the Apennines, with more spectacular manifestations especially in Emilia-Romagna and Sicily.
Mud volcanoes are geological structures that form following the leakage of clayey material onto the earth's surface, generally present in compressive tectonic contexts. The material emitted by mud volcanoes is composed mainly of clay mixed with a mixture of water and gas. The emission of these fluids towards the surface is linked to a geological process known as "sedimentary volcanism".
One of the fundamental requirements for the formation of mud volcanoes is the presence in depth of thick successions of poorly consolidated fine sediment, i.e. characterized by a lower density than the overlying rocks, such as to allow them to rise again. successions of sediment which, deposited in conditions of rapid and abundant sedimentation, do not allow the total expulsion of the interstitial fluids present. With the lithostatic pressure, caused by the overlying material, the interstitial pressure increases which in turn generates the migration of the fluids present in the sediment itself.
In nature there are various mechanisms capable of producing an increase in interstitial pressure such as to generate the formation of a mud volcano: from tectonic thrusts, especially compressive ones, to the dehydration of the clayey component, up to the formation of hydrocarbons. The gaseous hydrocarbons, migrating from the production area towards the surface, are subjected to a separation according to the molecular mass. Since methane has a much lower mass than other hydrocarbons, it reaches the surface faster. When this happens, the buried and unconsolidated material tends to rise up to the surface, giving rise to real lava flows similar to those produced by "real" volcanoes. In case of strong methane emission, the activity of mud volcanoes can be accompanied by gas explosions.
Figure 1. Position of the emission points and their localization with respect to the epicenter of the October 30 earthquake (star in the top right box).
The inspection of the mud emissions, carried out on 3 November, involved the municipal areas of Santa Vittoria in Matenano and Monteleone di Fermo (Figure 1), located between 38 and 44 km from the epicenter of the M 6.5 earthquake of 30 October . A new mud emission point was activated near some houses in Contrada San Salvatore, in the municipality of Santa Vittoria in Matenano.
Figure 2. Position of the emission points in Contrada San Salvatore in the Municipality of Santa Vittoria in Matenano.
For the description of the inspection of 3 November, link to the INGVterremoti Blog