Although European Space Agency’s comet-landing mission Rosetta ended on 30 September, the data gathered through it will keep teaching us about comets for a while.
Here are images taken by the Rosetta spacecraft’s camera when Comet 67P/Churyumov–Gerasimenko approached closest to the Sun in August. The comet became very active and outbursts occurred, a typical one thought to release 60–260 tonnes of material in just few minutes!
The outburst can be divided into three categories based on how their dust flow looks like, and the outbursts occurred both when the Sun had started to warm up the previously shaded surface, and after illumination of a few hours. 
So the outbursts could happen in at least two different ways.
Anyhow, they provide scientists insights of cometary lives and they look pretty cool.