Once you leave the volcano and return to the sea, the altar of snackrifice forgets your appeasement. I sacrificed the One True Earring and upon immediately returning to my boat, I received a warning quake and then an eruption within 8 segments (One True Earring should give 64). I repeated this several times and got the same result for each.
1. Enter Volcano during dry season 2. Sacrifice to the altar 3. Return to outer world and wait