I'm not that familiar with what the aftermath of significant volcanic eruptions, but I'm puzzled as to the rather large area indicated by the London VAAC. I;m aware that volcanoes can throw up vast quantities of solid material, but in particular, what kind of density of ash does the line delineate ?
Is this a
1) "Anyone on the ground in this area should close their windows and not go out" advisory
2) "Do not fly within this area because your engines may fail" advisory
3) "There might be a tiny bit of ash floating around, but nothing to have any particular impact on aviation" advisory ?