This footage is from an airplane that flew around the Grímsvötn eruption today. Lightning have been unusually common around this eruption. It is normal that lightning occur within the ash cloud, but during this one there are much more than usual. The highest occurance of lightning during the Eyjafjallajökull eruption was 22. This time it has gone up to 2198 lightning bolts.
This image shows the lightning count of the Icelandic Meteorology office. They’ve set up an entire page with up to date lightning information in English.