The author believes the 1971 eruption has been triggered by an uprise of the magma column which had for several decades fed the persistent activity located in both the NE crater and in the central crater's chasm. This uprise split open a set of en-echelon fissures first on the southern, then on the eastern upper slopes of Mt Etna. Degassing occurred at the uppermost part of the successive fissure systems, while the degassed lava flows poured out at the lowermost end. When the ENE tectonic fault-system came into operation and controlled the second half of the eruption, it led to the engulfment of the degassing vent and subsequently acted as an undergound channel through which the degassed lavas could flow freely until they poured out at the lower end of the fault zone. This fault zone follows one of the main tectonic trends which intersect below Mt Etna, the main other ones being oriented SW-NE and WSW-ENE.