6 Fuego, Guatemala (36)
Guatemala's Fuego had one of its most active years in decades, with multiple large eruptions. One of the biggest was in May, when the volcano not only produced pyroclastic flows and a 5 km / 16,000 foot ash plume, but also an impressive fire fountain and lava flow. These eruptions continued throughout the year, with over 30,000 people evacuated from the region around Fuego during September.
Image: The eruption plume from Fuego seen on September 13, 2012. NASA Earth Observatory.