The island of Kalliste was indeed beautiful but it was not defaced by the destruction caused by a tidal wave.
Kalliste was located in the southern Aegean Sea and served as a stopover for sea traffic coming from Crete, Egypt and all points south and east of mainland Greece ... the name of the island was changed from Kalliste to Thera and finally it became known as Santorini ... its odd shape is not due to the scars caused by a tidal wave ... the island suffered from a catastrophe which was totally predictable but not expected ... you know ... kinda like when you’re having a picnic in the vicinity of an ant hill ... you might expect the ants to carry away a few crumbs of food but you don’t really expect them to haul away your blanket, picnic basket, bull-dog and bicycle.
Okay ... before you get too far down the wrong road ... Kalliste/Thera was NOT eaten by ants ... not red ants ... not army ants ... not fire ants ... just forget the ant thing!
The catastrophe which reduced Kalliste/Thera to a parody of its former self was BIG ... but it was not a big wave ... in fact, the inhabitants of Kalliste/Thera would have been lucky if their island have been hit by a tidal wave ... the catastrophe which struck Kalliste/Thera caused tidal waves in other parts of the Aegean and Mediterranean Seas but they were mere low caliber side effects compared to the main event.
Try thinking more along the lines of what the god Hephaistos might do if he was really, really mad and decided to go bonkers on your island ... one minute you’re relaxing on the beach and the next minute you’re a thousand feet in the air looking down on a big hole in the ocean where your island used to be.