I really did think that something was going on at Grímsfjall volcano today. There was something going on. But whatever it was. That does not appear to be volcanic or related to any volcanic activity so far. Most likely this was a change to hydrothermal activity in Grímsfjall volcano or some movement of the ice covering Grímsfjall volcano close to the seismometer on top of Grímsfjall volcano.
But so far Grímsfjall volcano remains quiet.
The change in the tremor plot can be seen at the end of this tremor plot from the web site of Icelandic Met Office.
Update: This odd behaviour on Grímsfjall seismometer continues. So I am wondering if the false alarm might not be so false after all. But a eruption is not starting. It lacks the earthquakes of a magma pushing it’s way up the crust. But there is something going on at Grímsfjall volcano. That is for sure.