I see that many people think that Grímsfjall has started to deflate due to a drop in GPS measurements. But the “Up” part of the GPS measurements have been dropping over the past few days from about 85mm and down to about 65mm today.
As that may be true that the mountain has started to deflate from the top. It is not to say that deflation process has started at Grímsfjall. As the GPS data clearly shows that a inflation process has just moved from the top and to the south. But current GPS measurement clearly show that Grímsfjall is now inflating to the south (15mm today) with minor inflation to the east (about 15mm today). So it is clear that the magma is moving inside the volcano from one location to a other over the past few days. What that means is unclear at the moment. But it appears that the inflation to the south is speeding up at current time. This might get interesting soon in my opinion. Regardless if there is a eruption or not.
Data: ISGPS GFUM
Vatnajökull continued GPS data project from 2004.