IMPORTANT NOTE ABOUT SCENARIO 22
I reconstructed the reasons for my question about when the tsunami hits.
Environment in play: Whipporwills of Dunwich: if an investigator is reduced to 0 Stamina / Sanity while this card is in play, roll a die. On a 1, the investigator is devoured as the whipporwills catch his solul, and the terror level is increased by 1.
The Mythos card triggering the fourth doom token was another Environment, and I had three investigators in aquatic locations that could be possibly reduced to 0 stamina by the tsunami. Hence, if the tsunami triggers while the previous Mythos is still in play (for example, after monster movement but before resolving the Mythos special text), I could have had 3 investigators (potentially) devoured; if it's the last thing to be resolved, then the max penalty is an Injury each.
_______________
As a side note, I'd suggest (for normal or hard mode) that investigator reduced to 0 stamina by the tsunami must draw 1 (2?) Injuries in addition to any penalty for being knocked unconscious (after all, a Tsunami is not like slipping on a wet floor). This would force people to consider more the risk of being hit by the tidal wave & want abouse of it in order to recover Stamina for free