Old Gramps is kind of silently around during the book. Technically Momma leaves the kids with him when she leaves for Salina to look after Poppa, but all he really seems to do is sleep.
Sleeping may not be a bad thing for Grandpa to do though, as he has one of the most volatile savvies out there—the ability to create earthquakes. Grandpa is a good example of being able to scumble your savvy, i.e. keep his emotions in check. Can you imagine what would happen if he were to let what his feeling get the better of him? Yikes.
We get a glimpse of Grandpa Bomba's savvy in action when Mibs reminisces about Grandma Dollop's funeral. She says:
And finally, as the tears rolled down Grandpa Bomba's cheeks, the ground began to rumble. Headstones rocked and the folding chairs shuddered and rattled to and fro with all the folks still sitting in them holding tight. The earth shook violently […]. (26.8)
It is only during enormous grief that Grandpa allows his savvy to become unglued and wreak havoc, and it is probably due to how much control he uses the rest of the time that the damage isn't worse. Grandpa knows exactly how devastating his savvy could be if it got the better of him, and it is clear that he goes to great lengths to control it.
Grandpa is a reminder that with age comes wisdom, and that even if you feel awkward and unable to deal with certain parts of yourself, with time and dedication you can come to terms with who and how you are in the world.