One of the vulcanian explosions at Etna that have occurred April 8-9, 2013. Image: Video capture from video by Dr. Boris Behncke / INGV Etna has been full of surprises in 2013. Beyond the multitude of lava fountaining events the volcano has produced over the last few months, the Italian volcano surprised everyone by having a truly explosive (vulcanian) eruptions since yesterday (April 8). The eruption produced a dark grey plume but little to nothing in the way of lava fountains and flows. This is typical for vulcanian eruptions, where volcanic material is fragmented into ash, lapilli and bombs (the catch-all term is "tephra"), but dominated by fine ash. The explosions from these eruptions can be discrete "booms" that sound like canon fire. This video of the vulcanian explosions at Etna show the "shot" from the new Southeast Crater (check out this view as well). These eruptions are typically caused by material clogging the throat of the volcano until pressure builds to sufficient levels to force the blockage out as an explosive. Strombolian eruptions, which is what we more typically see at Etna, are formed by rapid exsolution of large bubbles in magma within the conduit of the volcano, so that is why they are accompanied by lava fountains and flows, unlike the vulcanian explosion like today's events. Speaking of Etna, if you haven't read up on the eruptions from April 3-4, be sure to check out the summary on the Osservatorio Etneo website.