The rock around this bolt has eroded significantly over the 15 years since it was placed!

Its not apparent in the photo and why would the rock have eroded around it ?

It looks very clear in the photo to me - the cement and bolt sitting quite rpoud of the rock. I'd guess it would be water erosion ... ?

I'm guessing thats a good 10-15mm of erosion - about 1mm per year, which is quite rapid. Dont know the route, but the bolt looks like its in one of the softer sandy bands of limestone towards the base of the cliffs?

I noticed the same thing on sport routes at Swanage last year. It is definately erosion rather than pullout. Some bolts there are in pretty soft rock. You can only hope that the people placing them used extra long (these are home made after all) bolts to compensate!

I'm not sure its practical, but maybe people should think about much deeper bolts than they have been if they are supposed to last the predicted lifetime.