It was reported yesterday (10-June-2020) in the news at Stöð 2 (Channel 2) that hydrothermal activity and gas output from Grímsfjall volcano has been increasing in recent months. This has been followed by increased earthquake activity in Grímsfjall volcano. There is now a risk of an eruption following a glacier flood from Grímsvötn lake but according to the Vísir news the lake is getting close to full or at the point where it can flood and empty the crater. That can start an eruption because of the pressure drop of the magma.
Seismic energy released by earthquakes in Grímsfjall volcano since last eruption in May 2011. Copyright of this image belongs to Icelandic Met Office.
It is expected by experts that next eruption in Grímsfjall volcano is going to be a normal eruption but the eruption in May 2011 was the largest eruption in Grímsfjall volcano in 138 years. Since last eruption of this size took place in the year 1873 and then it took 10 years before next eruption took place.
There has also been a minor increase in earthquake activity in Þórðarhryrna volcano but because of lack of data it is difficult to know what that means. Last eruption in Þórðarhyrna volcano ended in January 12, 1904. It erupted at same time as Grímsfjall volcano according to historical documentation.
Icelandic News in Icelandic
Merki um aukið útstreymi kvikugass úr Grímsvötnum (Vísir.is)