In October 2002 a new eruption began at Etna. Lava flows were issued from two different fissure systems on the NE and S flanks of the volcano. A continuous microgravity sequence, acquired at a station on the N slope (2800 m a.s.l.), shows a marked decrease (about 400 ¿Gal in less than one hour) about 4 hours before lava was first emitted from the eruptive fissures along the NE-Rift. This anomaly reversed soon afterward at a high rate. The strong gravity decrease is interpreted as the opening, by external forces, of a shallow fracture system 1 km W of the gravity station. Magma from the central conduit entered the new fracture system passively, and propagated through it towards lower portions of the NE-Rift. Both the arrangement of the new fracture system and the eruptive dynamics are in keeping with the inferred intrusive mechanism.