During the last few days Bobs behaviour has changed dramatically. Now we are seeing bursts of harmonic tremoring caused mainly by gas movements from the magma chamber to the vent that is Bob.
What has happened is that the new magma influx have slowed down considerably, or shut down completely. This has been noticed with the severely weakened, or missing low signal frequency harmonics (0.3, 0.6 and 1.2Hz) that was earlier visible at the EOSO and EGOM stations. Those signals where associated by me and others on here as coming from a great depth, possibly even from the active hotspot mantleplume.
We now know that there was an active mantleplume due to the high readings of UrTh (Uranium/Thorium) in the pyroclasts taken from Bob.
That the tremor is coming and going is most likely due to that internal pressure building has slowed down so much that it can not any longer keap up a constant pressure. Also that the pressure episodes comes more apart and generaly are weaker, are also a sign that Bob might be falling asleep.
Please notice that Bob is in no way dead, all it takes is new magma coming up and the eruption will pick up spead again. Like we saw a couple of weeks ago when everyone had started declaring Bobs death. So I will here post what the requirements are for calling Bob. Also, Bob might do quite a few things to surprise us still. So it is still worthwile to watch her.
All measurable signs must return to the baseline before onset of pre-eruptive behaviour. Harmonic tremor must be back to background noise for one week. GPS readings might not fall that much, but they must be stable for a week. Earthquakes will occur, but they will be weak, and are a sign of the magma chamber settling from the previously stressed and inflated state. There might very well be bubbling and a heatspot at the site of the vent(s) of Bob for a very long time, so remember that bubbling is not a sign for Bob being awake. There must though have been no pyroclasts or steaming visible for a week. Silt might though be suspended into the water by heat convection from the vent.
If all of this is the case for one week, then we can call Bob, and say that he is in intermission. After a year we can say that the volcano is dormant. We will never be alive when Bob is truly dead.
With these words I will stop writing actively about Bob unless he does something unexpected (again). Next post about Bob will most likely (if things continue the way I believe) be on the one week intermission day.
On a personal note
I would like to thank all of the lovely people from Spain that together with the rest of us has followed Bob. I hope that all of you will stay here and wait with the rest for the next interesting eruption.