On Wednesday 25-May-2016 a small earthquake swarm took place in Grímsfjall volcano (also known as Grímsvötn), none of the earthquakes that took place managed to reach the magnitude 1,0, many of the earthquakes where shallow and might be glacier movement, rather than actual earthquakes, but in I find it unlikely reason.
Since 2011 Grímsfjall volcano has been preparing for an eruption. The eruption in 2011 was the largest one in 140 years at least (VEI=4). The average time between eruptions in Grímsfjall volcano around 5 to 7 years (based on known eruption history). How long it is going to take until Grímsfjall volcano is ready for a new eruption is impossible to know, the current data however suggests that next eruption might not be that many years away. GPS data and other interesting information can be found here.