A seismic swarm began at 15:30 local time on 29 Sep; within 18 hours, 8 relatively large tectonic earthquakes of magnitudes around 5 and 17 volcano-tectonic quakes were recorded while the normal averages are only 6-14 tectonic and 4-8 volcanic quakes total for a month. Presumably, at least some of the quakes have been caused by magma pressurizing rocks and fracturing them at depth.
In historic times, Iya volcano has erupted at least 8 times, last in 1971, and it is one of Flores' most active volcanoes. Most explosions were small to moderate phreatic and phreatomagmatic events, i.e. (partially) driven by steam explosions of ground water in contact with magma. Iya's largest eruption occurred on 27 Jan 1969 and measured VEI 3, producing a violent explosion with pyroclastic flows. [less]