I am playing Shipwrecked Beta, so I am not sure if this happens in main branch as well.
I haven't found anything about this behaviour on wiki, or in bug tracker, so I assume it is a new bug.
Normally, 3 "warning" tremors happen before Volcano eruption (which starts at the time of 4th tremor).
However if I fully appeased Volcano after certain number of tremors - these tremors stop.
When they resume - I expect the countdown to begin anew (with 3 "warning" tremors before final 4th one and the eruption), however I get reduced number of tremors instead.
If I appeased volcano after first tremor, next time I only get 2 "warning" tremors before the eruption.
If I appeased volcano after second tremor, next time I get one "warning" tremor.
If it appears to not be a bug - I'll go edit a wiki page I guess.
1. During Dry Season, wait until tremors start. 2. After 2nd tremor, fully appease the volcano using Altar of Snekrifice - tremors will stop. 3. After some days, tremors start again - however instead of refreshing the countdown, you will only get one warning tremor (expected: 3) before final tremor + eruption.