Or maybe I'm mixing two stories in my mind.
Time travel where the characters are enclosed in a bubble - silver IIRC - and inside time progresses 'normally' but outside the bubble time speeds at some multiple, allowing those inside to seemingly skip dozens or hundreds of years in mere moments.
Memory seems to also have these spheres mobile, in that they can traverse large distances (inside a planetary atmosphere) within seconds.
Tossed into this mixed up memory mix is something about the spheres and a volcano.
Then... There was a gathering of the tribes picnic on a terraced lawn where attendees arrived via said silver spheres.
Dunno. Could be my memory is failing, but I seem to recall reading this on-line in the mid oughts, say 10-ish years ago.
Thanks for the use of your recollections.