Dynamics of volcanic eruptions: Understanding electric signatures for activity monitoring
Résumé
Aside common methods as seismology, ground deformation, and geochemistry,
electromagnetic and especially electric ones can efficiently be applied for imaging and
monitoring active volcanoes and hydrothermal systems that most often control the initial
eruptive phase. Surveys and mappings image ground fluids flow, faults systems, and
structural interfaces with anomalies up to several hundred of mV. Reiteration of surveys
highlights time and spatial evolution. Continuous networks must extend surveys when the
activity becomes stronger. Resolution in the data can reach a few microvolts as compared
to the tens of millivolts for surveys. Observations made on several volcanoes definitively
show that electric signals, up to some tens of millivolts, may appear some hours to a few
weeks before ground deformation and seismicity, and are related to some extent to the
location of the future activity. These transient signals may have a relationship with those
recorded aboard satellites. Both of them appear during the transition period between the
‘‘fatigue’’ and the ‘‘dynamical’’ stages, which announces accelerating and irreversible
processes.