2 Etna, Italy (125)
Etna started the year off with a bang -- multiple paroxysms over the first few months of 2012, extending a string that started in 2011. Some of these paroxysms were spectacular, sending lava flows snaking down the volcano (see above) and producing small pyroclastic flows during explosions when lava would interact with snow. Activity settled down as the year went on, although a new tephra cone grew within the Buoco Nuovo crater. Etna periodically steamed and glowed through the end of the year and a deep-seated seismic swarm closed out 2012 at Sicily's volcano.
Image: Lava flows from the February 9, 2012 eruption of Etna. Boris Behncke/Osservatorio Etneo.