The first image below shows minor ash emission during the activity from the NSEC on the 20th February 2013. At this time of the year, the slopes of Etna are used for skiing. In certain places you can see white snow poking through a fresh covering of black ash (as a result of the basaltic magma). The ash emissions from the NSEC are clearly separated from a lower area of steam. It is even possible to notice some incandescence near to the NSEC (just below the NSEC) and against the right edge of the image and half way down. Other images below this show much more vigorous activity with the first image on the left showing a clear lava fountain. The image to the right of this shows more clearly the incandescence I mentioned earlier and shows the likely cause of all the steam (the result of lava heating snow)! This could be indicative of a fissure or a lava flow with fast flowing lava allowing it spill up over the edges spectacularly. Although the images are not 100% revealing so I can't be certain.
For a discussion of the causes of strombolian and hawaiian activity please see a couple of my previous posts. Etna continues as one of the most active volcanoes on the Earth and will continue to provide a spectacular show for all of us over the coming months and far off into the future.