Monitoring Active Volcanoes with Infrasonic Arrays: from gas puffs to ash eruption and pyroclastic flow
Jeudi 2 décembre 2010 à 15h
En collaboration avec E. Marchetti(1), G. Lacanna(1), P. Poggi
(1)Dipartimento Scienze della Terra, Università di Firenze, via LaPira, 4, 50121 Firenze, Italy
(2)Istituto Nazionale Ottica Applicata - INOA, 50121 Firenze, Italy
Volcanoes are quite a prolific radiator of infrasonic waves (<20 Hz). Gas rapidly expanding in the atmosphere produce infrasound providing valuable insights into eruption dynamics The intensity of infrasonic waves can range from very low amplitude pressure signals (mPa) to violent shock waves (MPa). Large explosive volcanic eruptions typically generate a plume of hot ash and debris ejected into the stratosphere and inducing pressure perturbation with frequency content ranging from 0.1-4 Hz down to 1-2 mHz typical of gravity waves. These waves can be recorded thousands of kilometers away by distant stations. At distances of few km acoustic wavefield can be used to track the ash plume evolution providing the time history of the excess pressure and reflecting the explosive gas emission driving the plumeheight. This information could be used as input parameter in the simulations of the ash cloud dispersal in the atmosphere and could contribute to a correct risk. assessment for civil aviation. Moreover, the collapse of the ash column or of part of the volcanic edifice (dome) can trigger pyroclastic flows. Infrasound generated by these non-explosive non-point sources can be detected by arrays, providing crucial information to volcano monitoring and risk management. Volcano acoustics can be integrated with other geophysical measurements, particularly seismic, and may assist with their interpretation. Its continued use may lead to important understanding of the volcano dynamics and dividends in the assessment of volcano-related hazards.